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Woodsiaceae. Athyrium distentifolium, Alpine lady-fern. Fronds bi-pinnate, ovate-lanceolate, yellow-green 20 cm to over 100 cm, arising in a 'shuttlecock' from a central crown. Stipe straight, one fifth to one quarter the length of the blade with pale brown scales, usually broad, but occasionally narrow. Pinnae widely spaced near base of the frond, and sometimes deflexed, crowded near the tip, meeting the rachis at an angle of 900 at the midpoint of the blade, or slightly ascending. Pinnules broadest at the base, tapering to a point. Sori circular, with irregular filaments making up a rudimentary indusium when young, soon obscured as the sori grow. Sori concentrated in the upper part of the frond, becoming sparse towards the base. Number of sori varies with size of frond. Plants frequently infertile (McHaffie et al. 2002). Athyrium distentifolium var.flexile Newman's lady-fern. Fronds bi-pinnate, narrow, blue-green, 10-40 cm, arising from a central crown, erect or sharply angled near the base of the rachis to lie nearly flat against the substrate. Stipe short, one sixth to one eighth the length of the blade, often densely covered with broad, pale scales that may continue beyond the midpoint of the blade. Blade broadest near the base, or nearer the mid-point. Pinnae close together near base of frond, often strongly deflexed to at least half way up the frond. Uppermost pinnae widely spaced. Pinnules taper towards the base. Sori circular, sometimes with only a few sporangia; rudimentary indusium visible while the sorus is still immature. Sori concentrated at base of the frond, becoming less frequent towards the tip. Plants usually fertile (McHaffie et al. 2002). Athyrium distentifolium is a chionophilous fern that grows at altitudes or latitudes which ensure long-lying winter snow cover. Deep snow provides insulation from severe winters, and prevents early growth in a mild spring. Only a limited number of species can tolerate these conditions and this reduces competition. Although previously known as a Scandinavian and continental European species, A. distentifolium was not recognized in Britain until 1844 (Newman 1851). Within Britain it is found only in Scotland where it is confined to the remote Highlands. Soon after it was identified, another similar taxon of uncertain taxonomic status was described (Backhouse 1852). Subsequent research has determined that this is a recessive variety which is now known as A. distentifolium var.flexile. Both taxa are covered in this account.

The utility of EST-simple sequence repeats (EST-SSRs) was evaluated in the fern Athyrium distentifolium. From 1152 frond cDNA clones, 165 microsatellites, including di-, tri-, tetra and penta-nucleotide repeat motifs, were identified. Primer design was possible for 74 of the SSRs; subsequent screening of 10 loci on 186 individuals from six natural populations revealed between two and seven alleles per locus and expected heterozygosity (HE) estimates ranging from 0.027 to 0.809. Eight of these loci were further examined for cross-species and cross-generic amplification in other Woodsiaceae species, and polymorphic products were detected. EST-derived SSRs provide robust, informative and potentially transferable polymorphic markers suitable for biodiversity research.

○ Experiments were conducted to determine the genetic relationship between the alpine fern Athyrium distentifolium and the Scottish endemic taxon A. distentifolium var. flexile. ○ Segregation of the taxa was studied after growing sporophytes from spore families, and after selfing and crossing gametophytes. The growth of both gametophytes and sporophytes was measured under a range of nutrient regimes. ○ The distinction between the two taxa is due to variation at a single gene with pleiotropic effects expressed at both the sporophyte and gametophyte stages. A. distentifolium sporophytes (genotypes A D /A D or A D /A F ) are taller, have fewer fronds, and produce fewer spores than A. distentifolium var. flexile sporophytes (genotype A F /A F ). Gametophytes containing the A F allele have a 50% higher growth rate than those with the A D allele on a range of media. ○ The polymorphism may be maintained by a balance between selection for and against the A F allele at the gametophyte and sporophyte stages of the life cycle, respectively. Implications for the conservation of the A. distentifolium var. flexile taxon are discussed.

Odland, A. 1995. Frond development and phenology of Thelypteris limbosperma, Athyrium distentifolium, and Matteuccia struthiopteris in Western Norway. — Nord. J. Bot. 15: 225–236. Copenhagen. ISSN 0107–055X. The pattern of growth and phenology of Thelypteris limbosperma, Athyrium distentifolium, and Matteuccia struthiopteris fronds has been investigated, with particular emphasis on height increments of the sporophytes and the development of fertile fronds. In order to study both interspecific and intraspecific differences, fern stands along altitudinal gradients have been monitored. To investigate the initiation of fertility, fronds representing different developmental stages have been sampled. Climatic data have been collected with a data-logger during the study periods. The ferns show significant differences in growth pattern and phenology. Matteuccia struthiopteris has a growth curve that is best described as monomolecular, characterised by high growth rates during the early developmental stage, while the development of Thelypteris limbosperma and Athyrium distentifolium follow a logistic growth curve. The species need different periods of time to develop their fronds. The main frond elongation does not start before soil temperature has reached 7 C. After that, the growth is mainly controlled by air temperature. Within the interval when mean maximum temperatures are 8–20 C, all three ferns showed increased growth rates with increasing air temperatures, but the increase was greatest in M. struthiopteris. At higher temperatures, the growth rate of M. struthiopteris and T. limbosperma decreased. Athyrium distentifolium is characterised by producing sori at an early developmental stage. Fertile Matteuccia strurhiopteris fronds are developed at a much later developmental stage. Thelypteris limbosperma needs a longer period of time to produce mature fronds than the other species. The investigation indicates that plant growth and development are determined by both internal and external factors. It is concluded that growth rate, phenology, and the ability of ferns to produce mature fronds reveal close similarities with their response to environmental variables, and hence with their broad-scale geographical distributional patterns.

This paper presents results of a study on the synecology of Athyrium distentifolium. The investigation is based on phytosociological and ecological analyses of stands dominated by A. distentifolium within its whole distributional area in Western Norway. The distribution and floristic composition of the stands are related to different environmental parameters such as climate, soil and topography. The data are analysed by numerical methods, of which two-way indicator species analysis (TWINSPAN), canonical correspondence analysis (CCA), and simple discriminant functions (DISCRIM) are the most useful. Based on a TWINSPAN classification of the 211 investigated stands, 9 different groups (types) are distinguished. These belong mainly to three phytosociological alliances: Cryptogrammo-Athyrion alpestris (1 group), Lactucion alpinae (5 groups) and Vaccinio-Piceion (3 groups). The quadrats are in most cases very poor in species, even in edaphically rich areas. Soil richness in the stands is very variable. A. distentifolium may be dominant in edaphically rich areas and it is not a calciphobe species in W. Norway. Most stands show no signs of human influence. Length of snow-lie is assumed to be of major importance for the development and distribution of A. distentifolium stands.

Six tall herb and fern vegetation types in Roldal have been investigated. They are referred to the alliances Lactucion alpinae and Alno–Ulmion. Lactucion alpinae is divided into two suballiances, one oligotrophic to mesotrophic (Dryoptero–Calamagrostenion purpureae) to which are referred Athyrium distentifolium– Salix scrub, and Athyrium distentifolium meadow, and one eutrophic (Lactucenion alpinae) to which belongs Geranium sylvatkum meadow and Lactuca alpina meadow. Alnus incana forest, herb/fern and Matteuccia struthiopteris types belong to Alno–Ulmion. Lactucion alpinae is considered subalpine, whilst Alno Uimion is prealpine. The pre– and subalpine zones are considered oceanic sections of middle– and upper oroboreal vegetation zones.