Mountain holly fern (Polystichum scopulinum) COSEWIC assessment and status report: chapter 6

Biology

General

There is only limited information on the biology and ecology of P. scopulinum. Plants occurring on ultramafic habitats are adapted to tolerate low levels of calcium, nitrogen, phosphorus and molybdenum and high levels of magnesium, chromium and nickel (Kruckeberg 1969). These rock outcrop habitats are also characterized by shallow soils and a sparse groundcover thus creating xeric microclimates that also exclude many nearby species adapted to more mesic microclimates.

Some genetic information is available for the species. Polystichum scopulinum is an allopolyploid, thought to be derived, on morphologic grounds, from the hybridization of P. imbricans and P. lemmonii (Wagner 1979). The chromosome number for the species is 2n = 164.

Reproduction

As with most evergreen fern species, P. scopulinum often retains significant numbers of mature spores over the winter, to be released the following spring (Farrar 1976). Polystichum scopulinum also grows vegetatively by subterranean rhizome elongation often resulting in large clumps of clones. Because of the dry site conditions, which are not ideal for spore germination or gamete fertilization, most reproduction is probably by rhizome elongation. No prothalli (sexual plantlets in the reproductive cycle) were observed at the BC or QC sites.

Survival

No information available.

Physiology

No information available.

Movements/dispersal

The successful long-distance dispersal of spores of P. scopulinum is evident by the species’ occurrence across North America at widely disjunct localities on ultramafic substrates. Its absence from some areas of ultramafic bedrock may be a reflection of the hit-or-miss aspect of such a means of dispersal or reflect a contracting range. The species does not occur at either Mt. Baldy, British Columbia, 125 km to the east or in the Twin Sisters Range, Washington, 125 km to the southwest, where P. lemmonii is found (Kruckeberg 1969, Douglas 2002). It is also absent to the northwest in British Columbia where P. kruckebergii occurs on ultramafic rock outcrops. The nearest location in the United States to the British Columbia area of occurrence is in the adjacent state of Washington in the Wenatchee Mountains, part of the North Cascades Range (Kruckeberg 1969), a distance of about 230 km. The Quebec populations are even more dramatically disjunct (about 4000 km) from the nearest occurrences in British Columbia (Canada) and Utah (USA). The Newfoundland population is about 600 km east of the Quebec population across the Gulf of St. Lawrence.

Nutrition and interspecific interactions

No information available.

Behaviour/adaptability

No information available.

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