Lemmon’s holly fern (Polystichum lemmonii) COSEWIC assessment and status report: chapter 6

Biology

General

Other than general information, there is limited data on the biology of Polystichum lemmonii. However, the ultramafic habitat has been well-studied by Kruckeberg (1969). Plants of ultramafic habitats are adapted to tolerate low levels of calcium, nitrogen, phosphorus and molybdenum and high levels of magnesium, chromium and nickel (Kruckeberg 1969).

The successful long-distance dispersal of spores of P. lemmonii is evident by the distance to the nearest locations of the species in the adjacent US state of Washington. P. lemmonii occurs in the North Cascades Range of Washington in the Twin Sisters Range and the Wenatchee Mountains (Kruckeberg 1969), a distance of about 150 km to the southwest and 235 km to the south of Baldy Mountain, respectively. It is of interest to note, however, that the Tulameen River ultramafic site, where both P. kruckebergii and P. scopulinum occur (Kruckeberg 1969; Douglas et al. 2002b), does not contain P. lemmonii even though the Tulameen River site is halfway between Baldy Mountain and the Twin Sisters Range. The fact that both the Baldy Mountain and Twin Sisters sites are dunite outcrops, while the Tulameen River site is an olivine clinopyroxenite outcrop, may have a bearing on the distribution of P. lemmonii. Reproduction of P. lemmonii on the ultramafic ridges of the Baldy Mountain area is evident since about 30 percent of the 853 plants counted were relatively young (plant tufts less than four cm wide).

Some genetic information is available for the species. Polystichum lemmonii is a tetraploid (2n = 82) and thought to be one of the parents of both P. kruckebergii and P. scopulinum (Wagner 1979).

Reproduction

Sporophytes of P. lemmonii, as with other overwintering ferns, often retain significant numbers of mature spores over winter, to be released the following spring (Farrar 1976). Polystichum lemmonii also grows vegetatively by subterranean rhizome elongation, resulting in large clumps of clones. At the study site surveyed, P. lemmonii occurs on dry, sandy to gravelly, rapidly drained soil; such conditions are not ideal for either spore germination or gamete fertilization. Therefore, it can be inferred that most reproduction at the site is by simple rhizome elongation, likely because the species is stressed here at the edge of its range (Walker 1979). No prothalli were observed at the site.

Survival

About 30 percent of the 853 plants counted were relatively young (plant tufts less than four cm wide). The remainder of the plants are in clumps of various ages that appear to be increasing in size.

Physiology

Unknown

Movements/dispersal

The species spreads vegetatively by subterranean rhizome elongation and potentially disperses more widely by airborne spores.

Nutrition and interspecific interactions

Unknown.

Behaviour/adaptability