Blechnum spicant: Habitat and Vigor of Optimal, Marginal, and Disjunct Populations, and Field Observations of Gametophytes

Abstract

Species composition and abundance values for vascular plants were determined for 4 forest stands at Olympic Peninsula, Washington [USA], and a stand in northern Idaho where the homosporous fern B. spicant occurred. Vegetative vigor and reproductive vitality for B. spicant were estimated. Sterile frond length ranged from 47.9 cm at Twanoh to 19.0 cm at the Hoh Stand. Spore germination approached zero in the Hoh and Mason Mountain populations. The optimum habitat for B. spicant, represented by the Twanoh Stand, was wetter than mean sites in the Tsuga heterophylla zone, where Oplopanax horridum and Lysichitum americanum were abundant, Oxalis oregana was absent and Polystichum munitum was uncommon. Species composition, density and phenology were determined for mixed fern gametophyte populations at Lake Quinault. Gametophytes were first found in early fall, grew vigorously over the winter, and produced sporophytes through late spring. Female, bisexual and male gametophytes occurred in mixed-species populations at densities up to 4.5 cm-2. Sporophytes appeared shortly after development of archegonia on bisexual and female gametophytes. Polyembryony did not occur. As almost all archegoniate plants bore sporophytes in dense populations, competition among gametophytes was thought to be minimal. Dense populations of young sporophytes later occupied sites sufficient for single perennating sporophytes. Strong competition probably occurs between young sporophytes, and gametophyte reproductive mechanisms that increase heterozygosity may be selected in dense populations.