Biology of Athyrium distentifolium and A. flexile in Scotland

• Main Author: McHaffie, Heather
• Published: University of Edinburgh 1998
• Subjects: 580
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.666245

The Alpine Lady-fern, <I>Athyrium distentifolium </I>Tausch ex Opiz is found throughout the northern hemisphere. In Scotland, there is a smaller endemic form which was discovered in 1852 and has been named Newman's Lady-fern, <I>Athyrium flexile </I>(Newman) Druce. <I>A. flexile</I> is usually found with <I>A. distentifolium.</I> Although morphologically distinct, the taxonomic status of <I>A. flexile</I> has been the subject of continuing debate. This thesis aims to clarify the relationship between the two taxa. A morphometric analysis showed little overlap between the taxa for wild grown specimens. Comparisons between the spores and stomatal density showed small differences. The chromosome number was confirmed as being the same for both taxa. Gametophytes and sporophytes of both taxa grown at low nutrient levels demonstrated that the smaller <I>A. flexile</I> matured faster and became fertile while <I>A. distentifolium,</I> which is usually larger and more vigorous, remained small and infertile. The <I>flexile</I> taxon may therefore be an ecotype which is specially adapted to stressful environments. <I>A. flexile</I> is only found in a limited number of sites in the Central Highlands of Scotland which have a low-nutrient substrate. It appears it can only survive in habitats where the competition from <I>A. distentifolium</I> is reduced. The most significant discovery from the cultivation of spores from individuals of <I>A. distentifolium </I>was that some plants, when self-fertilised, produced both the <I>flexile </I>and <I>distentifolium</I> type of sporophyte. <I>A. flexile</I> plants always bred true when selfed. When gametophytes of <I>A. distentifolium</I> and <I>flexile</I> were given the opportunity to cross fertilise, some <I>A. flexile</I> gametophytes produced an <I>A. distentifolium</I> sporophyte. This suggests that <I>A. flexile</I> might be a homozygous recessive and does not justify species status.