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Recovery Strategy for the Silver Hair Moss (Fabronia pusilla) in Canada


Species assessment information from COSEWIC

Common Name: silver hair moss

Scientific Name: Fabronia pusilla Raddi Nov. et Rar. Plant. 2. in Atti dell' Acad. Di Scienze di Siena 9:230 1808

Status: Endangered

Last Examination and Change: November 2002

Canadian Occurrence: British Columbia

Reason for Designation: Silver hair moss is a small species that grows among other mosses, either as an epiphyte on trees or on rock faces. In Canada, it is known from two locations: one that is now submerged and a second associated with a cliff in southwestern British Columbia. The latter is the northernmost location for this species. Although the species was not relocated at its extant site during recent surveys, the expanse of available habitat at the only known sites, combined with small stature of the moss, suggests that the species may still be present in Canada.

Status History: Designated Endangered in November 2002. Assessment based on a new status report.

Description of the species

The silver hair moss is a tiny, creeping moss that grows in thin, flat mats. It has narrow, irregular branched stems with leaves pressed against the stem along their length, except for the leaf tips which tend to bend outwards. Leaves range from 0.4 to 0.85 mm long and from 0.2 to 0.35 mm wide. The leaves are somewhat egg-shaped and have long, clear leaf tips or awns, each ending in a distinctive long cell. The upper two-thirds of the leaf margins are bordered by sharp, cilia-like teeth, with the terminal cells of the teeth usually much longer than the lower cells. The clear awns and teeth give the plant a silvery to whitish-green cast.

The silver hair moss has male and female organs on the same stem. Because of the proximity of sex organs, sporophytes are common in most populations. The erect to somewhat curved stalk that bears the capsule is about 3 mm long. Its capsules are erect, ovate to obovate, with somewhat wrinkled bases when mature.

Although the marginal teeth of the leaves are not readily visible in the field under the low magnification of a hand lens, its diminutive size, long leaf tips, and the general whitish-green cast help to distinguish this species. Its small size and habit of growing with other larger pleurocarpous (creeping and freely branched) mosses may result in the silver hair moss being overlooked in field surveys.

This description is based on information from the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) (2002), Grout (1934), Lawton (1971), and Sharp et al. (1994). Figure 1 illustrates key features of this species and Figure 2 is a photograph of the plant including sporophytes. For additional illustrations refer to Lawton (1971) and Buck (1994).

Figure 1. Illustrations of the silver hair moss

Illustrations of the silver hair moss.

By T. McIntosh 2002. 1 and 2 are outlines of typical leaves (× ~80), 3 is a maturing capsule and upper portion of the seta (× ~40), and 4 shows details of the leaf margin and apex (× ~300; × ~80); illustrations redrawn from Lawton (1971) and Buck (1994), and from microscopic examination of material.


Figure 2. Plants of the silver hair moss with sporophytes (rehydrated from first provincial collection)

Plants of the silver hair moss with sporophytes (rehydrated from first provincial collection)

From Species at Risk Act (SARA) website (Environment Canada 2004; photograph by S. Ellis).

Populations and distribution

The silver hair moss has a western North American – western Europe/North African distribution, principally in Mediterranean-type, summer dry/winter wet climates. It has been found in western North America, Mexico, Europe, and North Africa (COSEWIC 2002). In North America, it has been reported from southern British Columbia, Washington, Idaho, Oregon, Colorado, New Mexico, Arizona, and California (Figure 3). The Canadian records are at the northern limit of the distribution of the silver hair moss in North America. It is more widespread and more plentiful southwards, especially in California.

In Canada, this species is restricted to southern British Columbia where it has been found at two locations: below McKee Peak at the west end of Sumas Mountain east of Abbotsford in the southwestern part of the province (Figure 4), and at Deer Park near Lower Arrow Lake in the Kootenay Valley in the south-central part of the province (Tan 1980). The Arrow Lake site is now submerged behind a dam (B.C. Tan, pers. comm., 2001), and the silver hair moss has not been collected from the area since Macoun’s collections in the late 1800s. It was last seen (and collected) at the Abbotsford site in March 1968. W.B. Schofield made two collections on the same date from sites near each other on Sumas Mountain (these are considered part of the same population; COSEWIC 2002); however, exact coordinates of these collections were not reported. It was not found by T. McIntosh and W.B. Schofield (who visited the site on two occasions with T. McIntosh) during fieldwork in 2001, 2003, and twice in 2005. Sites of similar sandstone habitat on Mount Maxwell, Saltspring Island, were surveyed by T. McIntosh in 2001, but this moss was not located.

Its North American distribution pattern, as well as its apparent preference for oak habitats in California, may indicate that the B.C. population is relictual in nature, possibly a remnant of a drier, oak-dominated ecosystem that was relatively extensive in the southern portions of the province during the warmer hypsithermal period some 6000–7000 years ago. A remnant stand of Garry oaks is present on Sumas Mountain about 10 km to the east of the silver hair moss site below McKee Peak.

No population data are available on the Canadian population of the silver hair moss (COSEWIC 2002; follow-up surveys did not relocate the species). Schofield did not collect any information about the population during his initial collection.


Table 1. Population data for the silver hair moss in Canada
SiteLocation coordinatesNumber of patchesLand tenure
Sumas Mountain (below McKee Peak)unknownunknownunknown
Arrow Lake AreaextirpatedN/AN/A

Globally, this species is tentatively considered common to uncommon but not rare (G4G5) and is Red-listed (S1) in British Columbia (B.C. Species and Ecosystem Explorer 2005). NatureServe Explorer (2005) lists itas not assessed for the United States (NNR), N1 (critically imperiled) ranking for Canada, S1 (critically imperiled) for Montana, S1 for Oregon, and S1 for British Columbia.

There are no reported estimations of global distribution and abundance for the silver hair moss. There are no detailed data on the size or trends of the Canadian population of this species as it has not been rediscovered since 1968.

Figure 3. Approximate distribution of the silver hair moss in North America and Canada

Approximate distribution of the silver hair moss in North America: southern British Columbia, Washington, Idaho, Oregon, Colorado, New Mexico, Arizona, and California

Gray area approximates the distribution in the United States, black dot is the Sumas Mountain Canadian location, and the circle is the extirpated Lower Arrow Lake location.


Figure 4. Distribution of silver hair moss in Canada

Distribution of silver hair moss in Canada: Sumas Mountain, extirpated Arrow Lake

X = Sumas Mountain site; E = extirpated Arrow Lake site.

Figure 5. Sumas Mountain site with approximate extent of sandstone cliffs noted by yellow dots

Sumas Mountain photo

Length about 1.5 km.

Needs of the silver hair moss

Habitat and biological needs and limiting factors

There is little information about the habitat needs for the silver hair moss in British Columbia or elsewhere. In British Columbia, the reported population of the silver hair moss (at the Abbotsford site) is restricted to semi-shaded, sandstone rock faces or crevices, often alongside other species of mosses, in particular Homalothecium spp., in low elevation, summer dry environments. However, the exact location, and thus habitat, for this collection has not been determined. It was reported from crevices of steep rocks of undetermined type at the Arrow Lake site (now under water). Southwards in North America, it has been found in similar habitats as well as on tree bark, especially oaks (including Garry oak).

Little is known about the biological attributes that may influence the recovery potential of the silver hair moss. Although the silver hair moss produces sporophytes and spores frequently across the southern portions of its range, sporophytes are not abundant in the two Sumas Mountain collections at the University of British Columbia. Thus, reduced spore production may limit recovery. Also, there is no information on spore dispersal distances, viability, or germination success for this species, although moss spores in this type of habitat are most frequently wind-dispersed. The closed habitat where this species lives may restrict wind dispersal of spores. There is no evidence of asexual reproduction by specialized propagules or by fragmentation, and this may also limit its ability to disperse and recovery.

Another limiting factor may be size--this very tiny moss is smaller than other moss species that grow with it. Because of this, it may not have the competitive ability that adjacent mosses possess, and may require open, relatively bare rock surfaces to survive.


Until this species has been relocated, the following are considered to be potential threats.

Urban development on Sumas Mountain

A large area of dry Douglas-fir/big-leaf maple forest below the probable location where the silver hair moss was found on Sumas Mountain has recently been developed for residential use. However, the cliffs where this moss was found are over 80 m above this area, and this activity may not have affected the population. The City of Abbotsford’s McKee Peak Planning Study indicates that much of the land above the probable location could be subject to urban development in the next 10–15 years. The proposed development is approximately 800 ha, so would result in a significant number of people living near the cliffs.

Recreational activities

Hiking is common along narrow trails beneath the cliffs but no damage to bryophyte populations of other species on the outcrops was observed. Some rock climbing to small ledges and grottos was observed, but this activity is minor. However, given that there is a new housing development in progress below the cliffs, and being planned above the cliffs, hiking and climbing activities will likely increase in the future, and may threaten the populations of this moss.

Natural rock face degradation

If the population of silver hair moss is extant, there are potential, but probably minor, natural environmental threats to the extant population of the silver hair moss, principally rock face degradation. However, it is unlikely that the potential natural threat of rock face degradation can be mitigated.

Knowledge gaps

Our knowledge of the biology and habitat of the silver hair moss in Canada is inadequate to define potential management activities that would protect and maintain populations. Descriptions and assessment of potential threats to this species are not well known or understood. Therefore, inventory, both of the known site as well as similar sites along the coast and possibly near Arrow Lake, is valuable.

If the species is rediscovered, an investigation of hiking use in the area is recommended.

More information is required on the general biology of this species, in particular precise population description information.

Although general characteristics for its habitat are known, more data are needed to fully describe potential critical habitat attributes. Little is known about characteristics of the habitat adjacent to the population. These sites should be surveyed as adjacent habitats may influence the health and status of silver hair moss.