Pine Broomrape (Aphyllon pinorum): COSEWIC assessment and status report 2024

Official title: COSEWIC assessment and status report on the Pine Broomrape (Aphyllon pinorum) in Canada

Committee on the status of Endangered Wildlife in Canada (COSEWIC)

Endangered

2024

 

COSEWIC assessment summary

Assessment summary - May 2024

Common name

Pine Broomrape

Scientific name

Aphyllon pinorum

Status

Endangered

Reason for designation

The Canadian population of this parasitic annual plant consists of fewer than 60 mature individuals where it remains in two forested areas on Vancouver Island at the northern extent of its North American range. In the past, plants have been lost due to logging, and currently it is threatened by recreational activities, especially trail building/maintenance, and increased ignition sources for forest fires. With a very small population and restricted distribution, this plant is at risk of extirpation from Canada.

Occurrence

British Columbia

Status history

Designated Endangered in May 2024.

COSEWIC executive summary

Pine Broomrape

Aphyllon pinorum

Wildlife species description and significance

Pine Broomrape (Aphyllon pinorum) is a parasitic annual forb that develops from a large subterranean tuber-like mass. It lacks chlorophyll and produces erect, branched stems with numerous tubular, yellowish to purplish flowers, and abundant tiny, dust-like seeds in its capsular fruits.

Aboriginal (Indigenous) knowledge

All species are significant and are interconnected and interrelated. There is no species-specific ATK in the report.

Distribution

Pine Broomrape is an uncommon species along the west coast of North America, from southern Vancouver Island south to California. Disjunct subpopulations also occur in the interior of the Pacific Northwest (northern Idaho, eastern Washington, and eastern Oregon) and the mountains of New Mexico.

Habitat

Pine Broomrape is closely associated with dry coniferous forest habitats, where it requires the presence of its host plant, Oceanspray, for successful seed germination and plant development. Canadian subpopulations are specifically associated with forests of Douglas-fir.

Biology

This is an annual species that reproduces primarily through self-fertilization, although it occasionally outcrosses via insect pollinators (bees). It is completely dependent as a parasite on its host, Oceanspray, from which it derives the water, minerals, and nutrients required for development. The minute seeds are well adapted for wind dispersal; however, dispersal distance may be reduced within the typically dense, forested habitats that the species occupies.

Population sizes and trends

Two extant subpopulations of Pine Broomrape are known in Canada, both of them from southern Vancouver Island, although a third subpopulation with inconclusive details is known from a historical collection. Little data on long- or short-term trends in these subpopulations have been published, but current estimates of abundance at the two known sites suggest that the entire Canadian population numbers fewer than 60 individuals.

Threats

The primary threats to this species in Canada include recreation (especially trail building/maintenance) and the potential loss of its forested habitats through stochastic events (for example, high-intensity fire). However, as both known subpopulations occur largely or entirely within protected areas (provincial and regional parks), they are afforded some level of protection from large-scale ecosystem impacts that could eliminate suitable habitat.

Protection, status, and recovery activities

Pine Broomrape currently has no legal protection in Canada. In British Columbia it is ranked as S1S2, or Critically Imperilled to Imperilled (2019), which earned it a place it on the provincial red list. At the global scale, NatureServe ranks this species as G4 (Apparently Secure; reassessed 2024). In Canada, all known subpopulations occur largely or entirely within protected parks.

Technical summary

Aphyllon pinorum

Pine Broomrape

Orobanche des pins

Range of occurrence in Canada: British Columbia

Demographic information:

Generation time (usually average age of parents in the population)

6 years

An annual plant, but similar species in Europe have been known to produce seed banks. Five years is the estimated half-life of the seed bank.

Is there an [observed, estimated, inferred, or projected] continuing decline in number of mature individuals?

Unknown

Limited and incomplete historical population estimates. Threat calculation projects a decline of between high (median 40%, 22%–70%) and low (median 3%, 1%–10%) over the next ten years.

[Observed, estimated, or projected] percent of continuing decline in total number of mature individuals within 3 years [or 1 generation; whichever is longer up to a maximum of 100 years]

Unknown

No evidence of decline, but decline projected based on threats.

[Observed, estimated, or projected] percent of continuing decline in total number of mature individuals within 5 years [or 2 generations; whichever is longer up to a maximum of 100 years]

Unknown

No evidence of continuing decline, but decline projected based on threats.

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last 10 years [or 3 generations; whichever is longer]

Unknown

There are limited and incomplete historical population estimates; however, some plants known to exist in 2003 were lost due to logging, but the net loss to the population is unknown.

[Projected, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations, up to a maximum of 100 years]

Unknown

Declines projected based on threat calculator.

[Observed, estimated, inferred, projected, or suspected] percent [reduction or increase] in total number of mature individuals over any period of 10 years [or 3 generations; whichever is longer, up to a maximum of 100 years], including both the past and future (up to a maximum of 100 years in future)

No evidence of population declines

No evidence of population declines. Threat calculation projects a decline of between high (median 40%, 22%–70%) and low (median 3%, 1%–10%) over the next ten years.

Are the causes of the decline clearly reversible?

Unknown.

It is unknown if plants will recolonize logged areas.

Are the causes of the decline clearly understood?

Yes

The loss of individuals is believed to have occurred due to the loss of habitat associated with wood harvesting.

Are the causes of the decline clearly ceased?

No

Wood harvest related and other forms of habitat loss may be causing the loss of undocumented individuals.

Are there extreme fluctuations in number of mature individuals

Unknown

As an annual species, likely experiences some inter-annual fluctuations in number of mature individuals in relation to yearly climatic variations, but the magnitude of any such fluctuations has not been described for Canadian occurrences.

Extent and occupancy information:

Estimated extent of occurrence (EOO)

25 km²

Based on a 1-km-wide linear polygon between the two subpopulations, which are 25 km apart.

Index of area of occupancy (IAO), reported as 2x2 km grid value

8 km²

Is the population “severely fragmented”, that is, is >50% of individuals or >50% of the total area “occupied” (as a proxy for number of individuals) in habitat patches that are both (a) smaller than required to support a viable subpopulation, and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse?

1. No
2. No

Both subpopulations occur in areas that are contiguous with adjacent areas of suitable habitat

Number of “locations” (use plausible range to reflect uncertainty if appropriate)

2

The two known subpopulations represent separate locations based on catastrophic wildfires.

Is there an [observed, inferred, or projected] continuing decline in extent of occurrence?

No

Insufficient data to assess potential declines.

Is there an [observed, inferred, or projected] continuing decline in area of occupancy?

No

Insufficient data to assess potential declines.

Is there an [observed, inferred, or projected] continuing decline in number of subpopulations?

No

Insufficient data to assess potential declines.

Is there an [observed, inferred, or projected] continuing decline in number of “locations”?

No

Insufficient data to assess potential declines.

Is there an [observed, inferred, or projected] continuing decline in [area, extent and/or quality] of habitat?

Yes

Quality of habitat noted to be declining along forest edges at Koksilah River due to extensive windthrow. Increases in human visitation may also be causing a decline in habitat quality.

Are there extreme fluctuations in number of subpopulations?

No

Both subpopulations appear to be well-established and persistent.

Are there extreme fluctuations in number of “locations”?

No

Both locations appear to be well-established and persistent.

Are there extreme fluctuations in extent of occurrence?

No

Both subpopulations appear to be well-established and persistent.

Are there extreme fluctuations in index of area of occupancy?

No

Both subpopulations appear to be well-established and persistent.

Number of mature individuals (by subpopulation):

1. Koksilah River Provincial Park
2. Sooke Potholes Regional Park
3. 'Cowichan River'

1. 5-7+
2. 41
3. unknown

Data from BC Conservation Data Centre. Collection data from Cowichan River from 1914 are imprecise.

Total

50 to 60

Data from BC Conservation Data Centre

Quantitative analysis:

Is the probability of extinction in the wild at least 20% within 20 years [or 5 generations], or 10% within 100 years]

Unknown

Calculation not done

Threats:

Was a threats calculator completed for this species?

Yes (see Appendix 1)

Overall assigned threat impact: High-Low (2023) which was adjusted from a calculated rank of High-Medium due to two of the contributing threats being at the low end of Low.

Key threats were identified as:

1. Fire and Fire Suppression (IUCN 7.1) – medium-low impact
2. Tourism and Recreational Areas (IUCN 1.3) – low impact
3. Recreational Activities (IUCN 6.1) – low impact
4. Other Ecosystem Modifications (IUCN 7.3) – low impact
5. Storms and Flooding (IUCN 11.4) – low impact

What limiting factors are relevant?

• The distribution of Pine Broomrape in Canada is limited by the presence of its host species, Oceanspray
• The small, isolated nature of the two subpopulations of Pine Broomrape in Canada presents a likely barrier to gene flow between them, rendering both subpopulations susceptible to factors such as genetic effects or pathogen spread

Rescue effect (from outside Canada):

Status of outside population(s) most likely to provide immigrants to Canada.

• WA: S3
• ID: S2

Listed as a species of concern in the two adjacent jurisdictions

Is immigration known or possible?

Unknown

Dispersal ability and limitations not studied

Would immigrants be adapted to survive in Canada?

Yes

Ecological conditions of nearest subpopulations are consistent with those supporting the species in Canada.

Is there sufficient habitat for immigrants in Canada?

Yes

Suitable habitat is extensive in the southern part of Vancouver Island.

Are conditions deteriorating in Canada?

Yes

Some habitat deterioration noted at Koksilah River along forest edges. Forest habitats on southeastern Vancouver Island are subject to considerable pressure from urban and agricultural development and are declining in overall extent.

Are conditions for the source (that is, outside) population deteriorating?

Unknown

Very little is known about the species in Washington, with only six records known

Is the Canadian population considered to be a sink?

No

Subpopulations are believed to be self-sustaining

Is rescue from outside Canada likely, such that it could lead to a change in status?

No

Long distance dispersal is not known for this species and the closest subpopulation in the USA is 52 km away, which includes 20 km of open ocean.

Wildlife species with sensitive occurrence data (general caution for consideration)

Could release of certain occurrence data result in increased harm to the Wildlife Species or its habitat?

No

Status history

COSEWIC

Designated Endangered in May 2024.

Status and reasons for designation:

Status

Endangered

Alpha-numeric codes

B1ab(iii)+2ab(iii); D1

Reason for change in status

Not applicable

Reasons for designation

The Canadian population of this parasitic annual plant consists of fewer than 60 mature individuals where it remains in two forested areas on Vancouver Island at the northern extent of its North American range. In the past, plants have been lost due to logging, and currently it is threatened by recreational activities, especially trail building/maintenance, and increased ignition sources for forest fires. With a very small population and restricted distribution, this plant is at risk of extirpation from Canada.

Applicability of criteria:

A: Decline in total number of mature individuals:

Not applicable.

Insufficient data to reliably infer, project, or suspect population trends.

B: Small Range and Decline or Fluctuation

Meets Endangered, B1ab(iii)+2ab(iii).

EOO of 25 km² and IAO of 8 km² are below the threshold for Endangered. There are only 2 locations, and there is projected continuing decline in quality of habitat.

C: Small and declining number of mature individuals

Not applicable.

Number of mature individuals (60) is below the threshold for Endangered. However, there is no evidence of continuing decline in the number of mature individuals.

D: Very small or restricted population

Meets Endangered D1 and Threatened D2

Number of mature individuals is estimated to be 60. Restricted to an IAO of 8 km² (or 2 locations) and prone to substantial decline from effects of human activities or stochastic activities within 1 to 2 generations if human-caused wildfire occurs at either of the subpopulations.

E: Quantitative analysis

Not applicable

Analysis not conducted.

If a species is proposed as Special Concern, Data Deficient, Extirpated or Extinct, list the applicable guidelines, examples, or other considerations from O&P Appendix E3.

COSEWIC history

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (2024)

Wildlife Species

A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)

A wildlife species that no longer exists.

Extirpated (XT)

A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A wildlife species facing imminent extirpation or extinction.

Threatened (T)

A wildlife species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)^*

A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)^**

A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)^***

A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.

^* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
^** Formerly described as “Not In Any Category”, or “No Designation Required.”
^*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006.

The Canadian Wildlife Service, Environment and Climate Change Canada, provides full administrative and financial support to the COSEWIC Secretariat.

Wildlife species description and significance

Name and classification

Current classification:

Major Plant Group: Angiosperms - Eudicots

Order: Lamiales

Family: Orobanchaceae

Genus: Aphyllon

Species: Aphyllon pinorum (Geyer ex Hooker) A. Gray

Subspecies in Canada: none

Common names:

English: Pine Broomrape (BC CDC 2022), Conifer Broomrape (Collins et al. 2020), Pinewoods Broomrape (Calflora 2022)

French: Orobanche des pins (NatureServe 2024)

Indigenous: unknown

Synonyms:

Orobanche pinorum Geyer ex Hooker

Phelypaea pinorum (Geyer ex Hooker) A. Gray

Myzorrhiza pinorum (Geyer ex Hooker) Rydberg

Originally described as Orobanche pinorum (Hooker 1851), Pine Broomrape is based on material collected from Idaho. Gray proposed the genus name Aphyllon (Brewer 1876). Schneider (2016) conducted a phylogenetic assessment of the broomrapes and concluded that the traditional circumscription of the genus was polyphyletic, necessitating a new genus name for the North American representatives. Gray’s Aphyllon was subsequently resurrected to accommodate those species.

Description of wildlife species

Pine Broomrape is a fleshy, essentially leafless, achlorophyllous, annual parasitic herb that grows from a large, rounded, coral-like subterranean tuber. The erect, variably coloured (brownish, purplish, yellowish, or cream-coloured) glandular-hairy stems are 10 to 30 cm to up to 50 cm tall (Ceska and Ceska 2003) and usually loosely branched above, bearing numerous tubular flowers that are each 13 to 19 mm long and have a somewhat flared, 5-lobed mouth. The leaves are greatly reduced and are represented by small, scale-like bracts along the stem and inflorescence branches. The fruits are egg-shaped capsules 6 to 7 mm long, each containing 500 to 2,000+ tiny tan to dark brown seeds. The senesced stems of this species often persist for months following flowering, sometimes even into the subsequent growing season when they can be found alongside the current year’s flowering stems.

Designatable units

Pine Broomrape is known from only two subpopulations on southern Vancouver Island that are within close proximity (approximately 25 km apart) and separated by fragmented areas of suitable habitat. The Canadian population is therefore considered a single Designatable Unit.

Special significance

Canadian subpopulations of Pine Broomrape represent the northernmost subpopulations of this species globally and are disjunct from other subpopulations by virtue of their occurrence on Vancouver Island. This is one of many plant species of the west coast of North America that reach their northernmost extent in the Georgia Depression of British Columbia, and as such is representative of a floristic diversity that is more typical of the western United States. Populations at the edge of a species range may be important for the future adaptive potential of the species (Lesica and Allendorf 1995).

Aboriginal (Indigenous) knowledge

Aboriginal Traditional Knowledge (ATK) is relationship-based. It involves information on ecological relationships between humans and their environment, including characteristics of species, habitats, and locations. Laws and protocols for human relationships with the environment are passed on through teachings and stories, and Indigenous languages, and can be based on long-term observations. Place names provide information about harvesting areas, ecological processes, spiritual significance or the products of harvest. ATK can identify life history characteristics of a species or distinct differences between similar species.

Cultural significance to Indigenous peoples

There is no species-specific ATK in the report. However, Pine Broomrape is important to Indigenous Peoples who recognize the interrelationships of all species within the ecosystem.

Distribution

Global range

Pine Broomrape is endemic to western North America (Figure 1), where it occurs primarily along the west coast of the United States from Washington south to northern California. Northern subpopulations are most common along the Cascade Mountains, with isolated subpopulations on the Olympic Peninsula and southern Vancouver Island. The southernmost subpopulations occur in San Luis Obispo County on the central coast of California. Separate subpopulations of this species occur inland in the northwestern United States, where it is found in northern Idaho, eastern Washington, and eastern Oregon. Occurrences in northern Idaho approach very closely to the Canadian border. Small disjunct subpopulations also occur in northern New Mexico. Pine Broomrape is uncommon throughout its range.

Figure 1. Global range of Pine Broomrape. Range based on distributional records from GBIF (2023) and iNaturalist (2023).

Canadian range

The species was first collected in Canada in 1914 (Glendenning 1918), with the collection label providing only a general locality of 'Cowichan River.’ The exact locality where this initial collection was made is unknown, and the species subsequently went uncollected on Vancouver Island until 2000, when it was rediscovered at Koksilah River Provincial Park (Ceska and Ceska 2003). Ceska and Ceska (2003) “returned to this area again the next summer and in the following three seasons we located more plants in the general area.” The localities of the plants observed during these surveys have been mapped by the BC Conservation Data Centre; some of the plants were found west of the park boundary on lands with timber harvesting rights and some occurred to the north. The northern portion has been afforded protection from logging; however, the sites to the west were recently logged. The area of previously reported occurrences was surveyed in 2023, but no plants were found outside the protected area, and this portion of the subpopulation is now considered eradicated. The subpopulation in the Koksilah Valley was the only known Canadian subpopulation for several decades until a second subpopulation was identified in Sooke Potholes Regional Park in 2021 (iNaturalist 2022; Figure 2). The use of iNaturalist has greatly increased the survey potential for this distinctive plant.

Figure 2. Range of Pine Broomrape in Canada. 1 = ‘Cowichan River’ (general locality); 2 = Koksilah River Provincial Park; 3 = Sooke Potholes Regional Park.

Population structure

COSEWIC defines population size as the total number of mature individuals of the taxon (COSEWIC 2021). Subpopulations are defined as “geographically or otherwise distinct groups in the population where there is little demographic or genetic exchange” (COSEWIC 2021). For Pine Broomrape, the subpopulation definition used is consistent with habitat-based plant element occurrence (EO) delimitation standards and is defined as a group of occurrences that are separated by less than 1 km, or if separated by 1 to 3 km, with no break in suitable habitat between them exceeding 1 km; or if separated by 3 to 10 km but connected by linear water flow and having no break in suitable habitat between them exceeding 3 km (NatureServe 2020). There have been no studies on variability within the species. There are no known studies on genetic structure within the Canadian population.

Extent of occurrence and area of occupancy

Current EOO:

Extent of occurrence (EOO) within Canada is 25 km², calculated using a minimum convex polygon of 1 km x 25 km that encompasses known records from 2000 to 2022 (Figure 2). Because the locality of the 1914 collection from the Cowichan River is not known, it was not included in the calculation of EOO.

Current IAO:

Index of area of occupancy (IAO) within Canada is 8 km², calculated using a 2 x 2 km grid drawn over known records from 2000 to 2022 (Figure 2).

Fluctuations and trends in distribution

Pine Broomrape has been surveyed infrequently in British Columbia since the initial observations were made at Koksilah River Provincial Park (Table 1), and surveys have been insufficient to detect trends in the population of this annual plant. The number of individuals observed at the Koksilah River subpopulation has fluctuated slightly (between 2 and 7 plants), but such minor variations can be attributed to variable survey effort as well as inter-annual fluctuations in environmental conditions. The Sooke Potholes subpopulation has been discovered only recently (2021), which precludes estimation of any long-term population trends.

Biology and habitat use

Life cycle and reproduction

Pine Broomrape is an annual holoparasitic plant species with a primarily autogamous breeding system (Ellis et al. 1999). Autogamy is characterized by selfing within a single plant, which is facilitated in Pine Broomrape by the positioning of the mature stamens, in which one or more of the filaments elongates during flowering to bring the anthers in contact with the fertile stigma (Ellis et al. 1999). There is evidence of occasional xenogamy (outcrossing) in this species based on flower visitations and subsequent pollen collection by small hymenopterans in Washington. In these subpopulations, potential pollination involving two species of solitary leaf‑cutting bees of the family Megachilidae (Cactus Mason Bee, Ashmeadiella cactorum, and Small Green Mason Bee, Osmia exigua) has been noted (Ellis et al. 1999). The predominance of Pine Broomrape pollen on the bodies of these two bee species following flower visitation suggested a degree of specificity in the pollination relationship. The low frequency of flower visitations by pollinators and the reduced seed set of pollinated flowers, however, indicates that autogamy likely remains the primary reproductive strategy of Pine Broomrape, at least in the subpopulations that were studied by Ellis et al. (1999).

Flower production in Pine Broomrape in Canada occurs during July and early August, although some plants may flower into late August. The fruiting capsules mature in late summer/early fall (August-September), followed by seed dispersal through the fall. The open capsules remain on the senesced stems throughout the late fall and winter, and are often still present during the following spring. Plants in Washington were noted to produce an average of 689±126 tiny seeds per capsule, for a mean of 71,656 seeds per flowering stem (Ellis et al. 1999). Although no information pertaining to seed longevity or seed-banking is available for Pine Broomrape, seeds of related and similarly holoparasitic species in the genus Orobanche from Europe can persist for up to 20 years in the soil (Habimana et al. 2014). The generation time is considered to be six years, based on the annual life history and an inferred half-life of five years for the seeds in the seed bank.

Pine Broomrape requires the presence of its host plant, Oceanspray (Holodiscus discolor), for germination and survival, and is unable to grow or develop in the absence of this species. During germination, broomrape seeds develop a single rootlet (“radicle”) that grows through the soil in search of the roots of its host species. This radicle, which grows only 1 to 5 mm in length and survives only a few days (Fernández-Aparicio et al. 2016), adheres to the host’s root and uses mechanical and enzymatic separation of the host plant’s cells to reach the central vascular cylinder of the root. A vascular connection with the host is ultimately established, through which the broomrape parasite can access water, minerals, and nutrients at the host’s expense. Once this vascular connection with the host is established, the developing seedling grows an underground storage organ (that is, tuber), from which an erect flowering stem ultimately emerges. Asexual reproduction is not demonstrated in this or any other members of the genus Aphyllon.

Habitat requirements

Throughout its range, Pine Broomrape is characterized as a species of dry coniferous forests and rocky slopes (Collins et al. 2020), and a review of label data from Canadian and other Pacific Northwest specimens supports this view. Canadian subpopulations are associated with low-elevation (< 200 m), rocky second-growth forests that are dominated by Douglas-fir (Pseudotsuga menziesii), with an understory comprised of species such as Sword Fern (Polystichum munitum), Salal (Gaultheria shallon), Red Huckleberry (Vaccinium parvifolium), Trailing Snowberry (Symphoricarpos hesperius), Oceanspray, Trailing Blackberry (Rubus ursinus), Twinflower (Linnaea borealis), Broad-leaved Starflower (Lysimachia latifolia), and Tall Oregon-grape (Mahonia aquifolium) (Figure 3; Figure 4). The moss layer within these habitats is generally extensive, being dominated by forest-floor species such as Oregon Beaked Moss (Kindbergia oregana), Stair-step Moss (Hylocomium splendens), Goose-necked Moss (Hylocomiadelphus triquetrus), and Menzies’ Tree Moss (Leucolepis acanthoneuron). The most important habitat requirement of Pine Broomrape is the presence of Oceanspray, which this species parasitizes exclusively. Oceanspray is found throughout southern British Columbia south of 51°N (Douglas et al. 2002; iNaturalist 2024). Forest ages at these subpopulations range from 40 to 90 years at Koksilah River to about 150 years at Sooke Potholes. The Koksilah River subpopulation is largely associated with a seasonally wet, forested gully that receives water inputs from winter through early summer but becomes dry at other times of year.

Both Canadian subpopulations of Pine Broomrape are associated with forests dominated by Douglas-fir. Subpopulations of Pine Broomrape south of Canada sometimes occur at higher elevations. However, where such populations have been documented in forests dominated by Subalpine Fir (Abies lasiocarpa) and Red Fir (Abies magnifica), Pine Broomrape is strictly associated with Oceanspray shrubs in both of these forest types.

Figure 3. Pine Broomrape plants at Sooke Potholes, August 2021. Plants are in a post-flowering state. Photos: Finn McGhee.

Figure 4. Pine Broomrape habitat at Sooke Potholes, August 2023. Left: typical habitat (note live plant at bottom left); Right: senesced stem from previous year.

Movements, migration, and dispersal

The seeds of Aphyllon species are extremely small (< 1 mm), dust-like, and are dispersed primarily by the wind (Plaza et al. 2004). As Pine Broomrape commonly occurs within the interior of closed-canopy forests where wind dispersal is less effective, as is the case at both Canadian subpopulations, its dispersal abilities are expected to be lower than related species that occur in more open environments.

Interspecific interactions

Pine Broomrape has an obligate holoparasitic relationship with Oceanspray. Although host switching has been noted as a driver of speciation in members of the related genus Orobanche (Thorogood et al. 2009), Pine Broomrape has only been documented parasitizing Oceanspray throughout its range (Schneider et al. 2016). Ellis et al. (1999) found that individual broomrape stems were generally within 5 m of an Oceanspray host and the species was not found in areas where the host plant was absent.

In 2003 or 2004, two larval insects of an unknown species were observed within the bulbous tuber of one plant, indicating the potential for insect herbivory to affect this species (BC CDC 2018). The observer concluded that these insects did not appear to be having a substantial negative effect on the plants.

Limiting factors

Limiting factors for this species are poorly understood. It is associated with habitats that are widespread on southern Vancouver Island and elsewhere in southern British Columbia that, presumably, could support many more subpopulations of this species than have been documented. The small, isolated nature of the two subpopulations of Pine Broomrape in Canada likely renders both subpopulations susceptible to factors such as genetic effects or pathogen spread. The small size of these subpopulations and the large distance between them also greatly inhibits any exchange occurring among the Canadian subpopulations, or between them and subpopulations in nearby Washington State. Furthermore, the distribution of Oceanspray inherently limits the available habitat for this species within its range; however, Oceanspray is a common forest shrub in southern British Columbia and the limitations it puts on the distribution of Pine Broomrape are likely minimal. The scarcity of Pine Broomrape, both within Canada and elsewhere in its range, may be more associated with aspects of the species’ physiology or biology rather than its habitat requirements, but this remains uncertain given the very limited data available. For example, there are no data available on the seed dispersal capabilities of this species within its forested habitat, which may limit its ability to establish new subpopulations or provide rescue to existing subpopulations.

Population sizes and trends

Data sources, methodologies, and uncertainties

Historical data pertaining to the two known subpopulations were provided by the B.C. Conservation Data Centre. These subpopulations were reassessed through field surveys in 2023.

Although southern Vancouver Island has been extensively surveyed botanically for more than 100 years, the recent discovery of the second subpopulation suggests that the species' entire range in Canada may not yet be fully known. The forested habitats that this species requires are typical of the dominant vegetation of southern Vancouver Island and render species-specific surveys challenging to conduct. Furthermore, a large portion of the landscape between the two known subpopulations falls within the Greater Victoria Water Supply Area, which has restricted access and is thus not as intensively surveyed as nearby areas. The host plant of Pine Broomrape, Oceanspray, is restricted in Canada to southern British Columbia (south of 53°N). It is quite likely that inherent elements of the species' biology, that are not well known, are more limiting than anything relating to its host`s distribution.

Abundance

Little data on long- or short-term trends in these subpopulations have been published. The total known Canadian population of Pine Broomrape comprises fewer than 60 plants, with between 2 and 7 plants being observed at the Koksilah River subpopulation and between 5 and 41 plants known from the Sooke Potholes subpopulation. At the time of its discovery, A. Ceska (pers. obs. 2000) noted that “quite a few more” plants were present at the Koksilah River subpopulation; however, these additional individuals were not quantified during that visit. Site visits in 2023 noted that flowering individuals from the current year were present alongside larger numbers of dead, senesced stems from the previous year(s); only stems from the current year were included in the population assessment for 2023. Current estimates of abundance at the two known sites suggest that the entire Canadian population numbers fewer than 60 individuals.

Fluctuations and trends

Survey effort for Pine Broomrape has been insufficient for the accurate assessment of population trends or fluctuations. Subpopulation estimates at Koksilah River over the past two decades have been few but have remained steady at between two and seven plants, although potential declines have been noted along the edges of harvested forests where windthrow has affected some Oceanspray shrubs that previously hosted the species (Ceska and Ceska 2003). The Sooke Potholes subpopulation has been known only since 2021, and the highly dispersed nature of the individuals, as well as the difficulty in detecting them, makes an accurate population assessment extremely challenging. Thus, no trends have been determined to date.

Continuing decline^{Footnote 1} in number of mature individuals:

No substantial population decline has been detected.

Evidence for past decline (3 generations or 10 years, whichever is longer) that has either ceased or is continuing (specify):

There are insufficient data to assess any past population declines.

Evidence for projected or suspected future decline (next 3 generations or 10 years, whichever is longer, up to a maximum of 100 years):

Insufficient data exist to project any short- or long-term population declines. This species may be susceptible to forest changes resulting from climate change (for example, hotter and drier summers, warmer winters), but no evidence of such changes has been detected.

Population fluctuations, including extreme fluctuations:

No evidence of strong population fluctuations has been detected at the two sites; however, such fluctuations may be expected to occur due to the annual life strategy of the species and its likely sensitivity to fluctuations in environmental conditions from year to year. Observations in 2023 noted that the number of dead stems from the previous year exceeded those of the current year at both sites, suggesting inter-annual variation in abundance.

Severe fragmentation

The habitat for Pine Broomrape at its Canadian sites is not considered severely fragmented, as the subpopulations are adjacent to extensive contiguous areas of comparable habitat (Figures 5 and 6). Some forest removal has happened in the vicinity of the Koksilah River subpopulation (Figure 6), and broomrape plants are absent from areas of young regenerating trees (< 20 years old). However, the forests in which this subpopulation occurs had been harvested in the past (current forest age ranging from 40 to 90 years), suggesting some ability of this species to persist in landscapes where forest harvesting is occurring.

Figure 5. Habitat continuity around known subpopulations of Pine Broomrape in Canada. Sooke Potholes. Yellow polygon delineates the distribution of known broomrape observations (BC CDC 2022). Base imagery from Google Earth.

Figure 6. Habitat continuity around known subpopulations of Pine Broomrape in Canada. Koksilah. Polygons delineate the distribution of known Pine Broomrape observations (BC CDC 2024). Observations are based on occurrences mapped in 2003. Top image 2005, bottom image 2023, shows areas of logging adjacent to known occurrences. The site to the west was not rediscovered during surveys in 2023. Base imagery from Google Earth.

Rescue effect

The Canadian subpopulations are disjunct from the nearest subpopulations on the Olympic Peninsula by approximately 52 km and 75 km, respectively, including about 20 km of open ocean across the Strait of Juan de Fuca. The closest known occurrence to Canada in Idaho is 96 km south of the border (GBIF 2023). Given the limitations of dispersal and the small size of the few nearby subpopulations, it is considered highly unlikely that the Washington subpopulations would be sufficient to rescue the Canadian population.

Threats

Historical, long-term, and continuing habitat trends

As both Canadian subpopulations of Pine Broomrape occur largely or entirely within protected parks, no substantial changes to habitat conditions (apart from natural succession) are expected to affect the majority of the individuals. Habitat degradation has been noted in some areas of Koksilah River Provincial Park, where windthrow along forest edges has negatively impacted areas of suitable habitat. As well, trail maintenance and construction, largely associated with mountain bike use, is widespread at Koksilah Park and may have impacted some individuals in the past. Some individuals of the Koksilah River subpopulation historically occurred and may still occur on private land outside of the park boundary, making these susceptible to potential future forest harvesting or housing development.

Current and projected future threats

Pine Broomrape is vulnerable to the cumulative effects of various threats, especially those associated with recreational activity (for example, trail maintenance, trampling). The nature, scope, and severity of these threats have been described in Appendix 1, following the IUCN-CMP (International Union for the Conservation of Nature – Conservation Measures Partnership) unified threats classification system (see Salafsky et al. 2008 for definitions and Master et al. 2012 for guidelines). The threat assessment process consists of assessing impacts for each of 11 main categories of threats and their subcategories, based on the scope (proportion of population exposed to the threat over the next 10-year period), severity (predicted population decline within the scope during the next 10 years or 3 generations, whichever is longer up to ~100 years), and timing of each threat. The overall threat impact is calculated by taking into account the separate impacts of all threat categories and can be adjusted by the species experts participating in the threats evaluation.

The overall threat impact for Pine Broomrape is considered to be High-Low, corresponding to an anticipated further decline of between high (median 40%, 22%–70%) and low (median 3%, 1%–10%) over the next 10 years. These values are to be interpreted with caution, as they may be based on subjective information, such as expert opinion, although efforts have been made to corroborate the scores with available studies and quantitative data.

The identified threats to pine broomrape in Canada are as follows:

Fire and fire suppression (IUCN 7.1) – medium to low impact

Pine Broomrape is associated with mature coniferous forests, which are susceptible to forest fires that could potentially result in the extirpation of an entire subpopulation. Although forest fires on southern Vancouver Island are rare to infrequent, particularly near areas of human settlement such as those occupied by Pine Broomrape, fire frequency or intensity may be expected to increase with the warmer and drier conditions associated with climate change. A large number of visitors to Sooke Potholes during hot dry periods increases the ignition sources.

Tourism and recreation areas (IUCN 1.3) – low impact

The presence of plants along the edges of established trails in both subpopulations makes them susceptible to any efforts to upgrade or widen these trails, particularly where the trails are unofficial but could potentially become official at some point in the future (as is the case with the Sooke Potholes subpopulation).

Recreational activities (IUCN 6.1) – low impact

Both Canadian subpopulations of Pine Broomrape occur largely or entirely within parks with considerable levels of recreational activity. Individual plants have been noted to occur alongside trails at both subpopulations, making them susceptible to factors such as trampling.

Other ecosystem modifications (IUCN 7.3) – low impact

Invasive plants pose a minor threat to the Sooke Potholes subpopulation. Scotch Broom (Cytisus scoparius) occurs at a low density in the vicinity of the subpopulation. The removal of danger trees along trails, particularly within Sooke Potholes Regional Park, has the potential to impact broomrape plants if the trees were felled on top of the subpopulation. However, the long-term effects of such an incident would likely be minimal for this annual plant.

Storms and flooding (IUCN 11.4) – low impact

Both subpopulations are potentially threatened by storms and associated flooding or erosion. The Sooke Potholes subpopulation occurs above a riverside cutbank that, with a sufficiently high flow event, could be eroded or otherwise compromised and could result in the loss of some or all of the plants. At the Koksilah River subpopulation, scattered plants have regularly been noted along a forested gully that receives water inputs during the winter and could be subject to erosion during a particularly severe event.

Temperature extremes (IUCN 11.3) – unknown impact

Extreme temperature events within the Canadian range of Pine Broomrape have increased in frequency and magnitude in recent decades and have impacted some plant species within this area (Seebacher 2007). Ecological changes resulting from temperature extremes and other climate change factors could potentially impact the species or its plant host (Oceanspray); however, insufficient data are available for this to be evaluated.

Number of threat locations

Two threat locations are identified for Pine Broomrape in Canada, representing the two known subpopulations.

Protection, status, and recovery activities

Legal protection and status

Pine Broomrape is not currently protected under any legislation in Canada. It is not covered under the Convention on International Trade in Endangered Species (CITES) or the United States Endangered Species Act.

Non-legal status and ranks

Pine Broomrape is ranked globally as Apparently Secure (G4, reassessed 2024) by NatureServe (2024), and is red-listed (S1S2; Critically Imperilled to Imperilled) in British Columbia, following a 2019 assessment by the British Columbia Conservation Data Centre (BC CDC 2022). In the United States, this species is ranked as S3 (Vulnerable) in Washington, S2 (Imperilled) in Idaho, S1 (Critically Imperilled) in Nevada, and S4 (Secure) in Oregon; it is unranked in California and New Mexico (NatureServe 2024). It has not been assessed by the International Union for the Conservation of Nature (IUCN).

Land tenure and ownership

Both known Canadian subpopulations occur largely or entirely within protected parks (Koksilah River Provincial Park/Hwsalu-utsum Provincial Park and Sooke Potholes Regional Park). However, some individual plants have been noted on private lands adjacent to Koksilah River Provincial Park in the past. The historical 1914 collection from the Cowichan River does not provide sufficient locational information to determine land ownership at that site.

Information sources

References cited

BC CDC. 2018. British Columbia Conservation Data Centre: Species Occurrence Report (Shape ID: 2218). Website: https://a100.gov.bc.ca/pub/eswp/eoMap.do?id=15467 [accessed February 2023].

BC CDC. 2022. British Columbia Conservation Data Centre: B.C. Species and Ecosystems Explorer. Website: https://a100.gov.bc.ca/pub/eswp/ [accessed December 2022].

Brewer, W.H. 1876. Botany, Vol.1. Geological Survey of California. University Press, Cambridge, Maine. 628 pp.

Calflora. 2022. Calflora: A non-profit database providing information on wild California plants. Website: https://www.calflora.org/ [accessed December 2022]).

Ceska, A. and O. Ceska. 2003. Pine Broomrape (Orobanche pinorum) at Koksilah Ridge, Vancouver Island. The Victoria Naturalist 60(3):6.

Collins, L.T., A.E.L. Colwell, and G. Yatskievych. 2020. Orobanche. In, Flora of North America North of Mexico, Vol.17. Website: http://floranorthamerica.org/Orobanche [accessed December 2022].

COSEWIC. 2021. Instructions for the preparation of COSEWIC status reports. 39 pp. Available online: https://COSEWIC.ca/index.php/en/instructions-preparing-status-reports.html [accessed March 2023].

Douglas, G.W., D. Meidinger, and J. Pojar. 2002. Illustrated Flora of British Columbia. Volume 8: General Summary, Maps and Keys. British Columbia Ministry of Sustainable Resource Management and British Columbia Ministry of Forests, Victoria, British Columbia. 457 pp.

Ellis, M.W., R.J. Taylor, and R.J. Harrod. 1999. The reproductive biology and host specificity of Orobanche pinorum Geyer (Orobanchaceae). Madroño 46(1):7-12.

Fernández-Aparicio, M., X. Reboud, and S. Gibot-Leclerc. 2016. Broomrape weeds. Underground mechanisms of parasitism and associated strategies for their control: A review. Frontiers in Plant Science 7:135.

GBIF. 2023. Global Biodiversity Information Facility. Website: https://www.gbif.org/ species/3173289 [accessed February 2023].

Glendenning, R. 1918. An annotated checklist of the flowering plants and ferns, native and introduced, growing without cultivation in the Cowichan District, Vancouver Island, B.C. Cowichan Field Naturalists’ Club, Bulletin Number 1. 20 pp.

Habimana, S., A. Nduwumuremyi, and J.D. Chinama R. 2014. Management of Orobanche in field crops – A review. Journal of Soil Science and Plant Nutrition 14(1):43-62.

Hooker, W.J. 1851. Hooker’s Journal of Botany and Kew Garden Miscellany. 384 pp.

iNaturalist. 2022. Photo of Aphyllon pinorum by Finn McGhee. Website: https://www.gbif.org/species/3173290 [accessed December 2022].

iNaturalist. 2024. Distribution of Oceanspray (Holodiscus discolor) in Canada. https://inaturalist.ca/observations?place_id=6712&subview=map&taxon_id=53414 [accessed April 2024].

Lesica, P., and F.W. Allendorf. 1995. When are peripheral populations valuable for conservation? Conservation Biology 9: 753-760.

Master L., D. Faber-Langendoen, R. Bittman, G.A. Hammerson, B. Heidel, L. Ramsay, K. Snow, A. Teucher, and A. Tomaino. 2012. NatureServe conservation status assessments: factors for evaluating species and ecosystems risk. NatureServe, Arlington, Virginia. Website: https://www.natureserve.org/publications/natureserve-conservation-status-assessments-factors-evaluating-species-and-ecosystem [accessed February 2023]

Musselman, L.J., and W.F. Mann. 1976. A survey of surface characteristics of seeds of Scrophulariaceae and Orobanchaceae using scanning electron microscopy. Phytomorphology 26:370-378.

NatureServe. 2020. Habitat-based plant element occurrence delimitation guidance. Website: https://www.natureserve.org/sites/default/files/eo_specs-habitat-based_plant_delimitation_guidance_may2020.pdf [accessed March 2023].

NatureServe. 2024. NatureServe Explorer. Website: https://explorer.natureserve.org/ [accessed April 2024].

Plaza, L., I. Fernández, R. Juan, J. Pastor, and A. Pujadas. Micromorphological studies on seeds of Orobanche species from the Iberian Peninsula and the Balearic Islands, and their systematic significance. Annals of Botany 94(1):167-178.

Salafsky, N., D. Salzer, A.J. Stattersfield, C. Hilton-Taylor, R. Neugarten, S.H.M. Butchart, B. Collen, N. Cox, L.L. Master, S. O’Connor, and D. Wilkie. 2008. A standard lexicon for biodiversity conservation: unified classifications of threats and actions. Conservation Biology 22: 897-911.

Schneider, A.C. 2016. Resurrection of the genus Aphyllon for New World broomrapes (Orobanche s.l., Orobanchaceae). PhytoKeys 75:107-118.

Schneider, A.C., A.E.L. Colwell, G.M. Schneeweiss, and B.G. Baldwin. 2016. Cryptic host-specific diversity among western hemisphere broomrapes (Orobanche s.l., Orobanchaceae). Annals of Botany 118(6):1101-1111.

Seebacher, T.M. 2007. Western redcedar dieback: Possible links to climate change and implications for forest management on Vancouver Island, B.C. Master’s Thesis, Forestry Dept., University of British Columbia, BC. 125 pp.

Thorogood, C.J., F.J. Rumsey, and S.J. Hiscock. 2009. Host-specific races in the holoparasitic angiosperm Orobanche minor: implications for speciation in parasitic plants. Annals of Botany 103:1005-1014.

Collections examined

The following specimen was examined digitally: Glendenning; 1914; ‘Cowichan River’; RBCM 4597.

Authorities contacted

• Fairbarns, M. Conservation Biologist. Aruncus Consulting. Victoria, British Columbia
• Fertig, W. Collections Manager. Marion Ownbey Herbarium, Washington State University. Pullman, Washington
• Govindarajulu, P. Unit Head. Species Conservation Unit, Ministry of Environment and Climate Change Strategy. Victoria, British Columbia
• Ilves, K. Beaty Centre for Species Discovery, Research and Collections, Canadian Museum of Nature. Ottawa, Ontario
• Lapointe, R. Manager. Species at Risk and Regulatory Affairs, Environment and Climate Change Canada, Canadian Wildlife Service. Pacific Region, Delta British Columbia
• Marr, K. Botany Curator. Royal British Columbia Museum. Victoria, British Columbia
• McDonald, R. Senior Environmental Advisor. National Defence. Ottawa, Ontario
• McGhee, F. Amateur Botanist. Victoria, British Columbia
• Miller, J. Lead Botanist. Washington Natural Heritage Program. Olympia, Washington
• Penny, J.L. Program Botanist. British Columbia Conservation Data Centre. Victoria, British Columbia
• Shepherd, P. Species Conservation and Management Ecosystem Scientist III. Parks Canada. Vancouver, British Columbia
• Starzomski, B. Ian McTaggart-Cowan Professor of Biodiversity Conservation and Ecological Restoration, School of Environmental Studies, University of Victoria. Victoria, British Columbia
• Strickland, J. Botany Data Coordinator. Idaho Department of Fish and Game. Boise, Idaho
• Ventrella, N. Botanist. Navajo Nation Department of Fish and Wildlife, Navajo Natural Heritage Program. Flagstaff, Arizona

Acknowledgements

Funding for the preparation of this report was provided by Environment and Climate Change Canada. The following authorities provided valuable data and/or advice during the preparation of this assessment: Jenifer Penny (B.C. Conservation Data Centre) provided existing survey results and historical data from British Columbia; Jesse Miller (Washington Natural Heritage Program), Walter Fertig (Washington State University), and Jim Strickland (Idaho Department of Fish and Game) provided information pertaining to the species in the northwestern United States; Finn McGhee and Matt Fairbarns (Aruncus Consulting) provided updated information on the recently discovered Sooke Potholes subpopulation of Pine Broomrape; Brian Starzomski (University of British Columbia) provided additional information on the Koksilah subpopulation; and Ken Marr (Royal British Columbia Museum) provided access to digital scans of the original 1914 Canadian specimen of Pine Broomrape from the Cowichan River.

Biographical summary of report writer(s)

Jamie Fenneman is a botanist and ecologist with EcoLogic Consultants Ltd., and currently resides in Courtenay on Vancouver Island, B.C. His work focuses primarily on biodiversity assessments, rare species surveys, planning and mitigation for rare plants, and long-term ecological monitoring. He has a formal academic background in plant taxonomy, including a doctorate from the University of British Columbia, and has been an active contributor to the floristic study of British Columbia for over two decades. Much of his work involves the survey and documentation of at-risk plants in British Columbia, and he works regularly with the B.C. Conservation Data Centre to maintain an accurate and up-to-date assessment of the floristic diversity of the province.

Appendix 1. Threats assessment for pine broomrape

Threats assessment worksheet

Species or Ecosystem Scientific name

Pine Broomrape Aphyllon pinorum

Element ID

1052532

Elcode

PDORO040B0

Date

8/31/2023

Assessor(s)

Bruce Bennett (VPSSC Co-chair, facilitator), Del Meidinger (VPSSC Co-chair), Jamie Fenneman (report writer), Varina Crisfield, Rebekah Neufield (VPSSC members), Morgan Davies (CRD), Rosana Soares (ECCC Science Officer), Carrina Maslovat (BC), Matt Fairbarns (Consultant)

Assigned overall threat impact

BD = High - Low

Impact adjustment reasons

Greatest impact on population would be fire, but there is uncertainty regarding the likelihood of fires. The other threats are a Low impact overall, as some are at the lower end of Low. With only two subpopulations, losing one to fire would have a large impact on the Canadian population.

Overall threat comments

Annual species; Orobanche seeds in Europe are viable for decades; most seeds are likely only viable for a short time; generation time = one plus 5 = 6 years; three generations ~ 15 to 18 years. Canadian population 50 to 60 plants. Most of population at Sooke Potholes park, in two patches, about 40 m apart; Koksilah subpopulation is more scattered.