Athyrium distentifolium Tausch ex Opiz ( A. alpestre (Hoppe) Rylands ex T. Moore‐non‐Clairv.) including A. distentifolium var. flexile (Newman) Jermy
2005; Wiley; Volume: 93; Issue: 4 Linguagem: Inglês
10.1111/j.1365-2745.2005.01037.x
ISSN1365-2745
Autores Tópico(s)Plant and animal studies
ResumoWoodsiaceae. 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 90° 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. Within the British Isles, Athyrium distentifolium is found only in Scotland (Fig. 1) from 455 m to over 1220 m a.s.l. (Preston et al. 2002) on open screes with extended snow cover in the central and northern Highlands. Growing in the same habitat, but found only at a few sites, is A. distentifolium var. flexile (Fig. 2). This taxon has only ever been recorded in Scotland and occurs across the central Highlands from 600 m to over 900 m a.s.l. (Preston et al. 2002). A. distentifolium has a disjunct circumpolar arctic-montane distribution (Preston & Hill 1997), which is clearly displayed in its European ranges (Fig. 3). In south-east Greenland it is found on the coast (Devold & Scholander 1933) but in Austria it is found up to 2770 m a.s.l. (Polatschek 1997) (Fig. 3). The North American plants with longer pinnules are sufficiently distinct to have been named A. distentifolium ssp. americanum (Butters) Hultén (Flora of North America editorial committee 1993). The distribution of Athyrium distentifolium in the British Isles. Each dot represents at least one record in a 10-km square of the National Grid: (○) pre 1950; (•) 1950 onwards. Mapped by H.R. Arnold, using Dr A. Morton's DMAP software, Biological Records Centre, Centre for Ecology & Hydrology, Monks Wood, mainly from data collected by members of the Botanical Society if the British Isles. The distribution of Athyrium distentifolium var. flexile in the British Isles. Each dot represents at least one record in a 10-km square of the National Grid: (○) pre 1950; (•) 1950 onwards. Mapped by H.R. Arnold, using Dr A. Morton's DMAP software, Biological Records Centre, Centre for Ecology & Hydrology, Monks Wood, mainly from data collected by members of the Botanical Society if the British Isles. The European distribution of Athyrium distentifolium on a 50-km square basis: (•) post 1930 records (×) pre 1930 records. Reproduced from Atl. Fl. Eur. (1) by permission of the Committee for Mapping the Flora of Europe and Societas Biologica Fennica Vanamo. In Scotland, Athyrium distentifolium grows only in sites where snow lies for extended periods during the winter. Snow can lie on the fern beds from October until May or even June. Precipitation on Athyrium distentifolium snowbed vegetation in the period 1941–70 varied from 1600–3200 mm in the west to 1200–1600 mm in the east Grampians. During the same period in the Central and North-west Highlands the January mean minimum temperature (screened at 1.25 m), was −5.0 °C, with a mean maximum of 1.0 °C (corrected by 0.5 °C and 0.7 °C, respectively, for each 100 m to give approximate temperatures at altitudes of around 800 m). The July mean minimum for the same period was corrected to nearer 6.0 °C, with a mean maximum corrected to 12.4 °C. The mean number of days with snow lying was 60–100 days in the Central Highlands. The snow did not lie for so long in the North-west Highlands, with a mean of 40–60 days (Meteorological Office 1979). These conditions combine to give cool summers, and extended snow cover in winter. In a mild spring at Glen Prosen in 1997, the ferns started to grow prematurely and were severely frosted (McHaffie 1998a). This illustrated the need for the protection of snow cover and the role it plays in controlling excessively early growth. Below snow cover an even temperature is maintained. Marchand (1987) established that beneath 40–50 cm of snow, small changes in density of the snow are unimportant and the temperature is almost constant at zero. In the Cairngorms plants of both taxa grow on granite. Elsewhere the rocks are part of the Moine series, which are mostly acidic, or of Dalradian metamorphosed rocks of sedimentary origin, which can include limestone (Institute of Geological Sciences 1977, 1979; British Geological Survey 1987). Pl. Comm. Scot. gives a surface pH range of 4.8–5.4 from 22 Athyrium distentifolium sites in the central and north-west Highlands. The screes are free-draining but melt-water and seepage maintain an adequate level of moisture. Soil samples from field sites in the Central Highlands ranged from pH 3.2–4.5 (McHaffie 1999). Two types of A. distentifolium communities were distinguished. The first is similar to McVean's Tall herb association (McVean 1964) on calcareous soil with rare Cicerbita alpina, frequent Dryopteris expansa, D. filix-mas, Polystichum lonchitis, Rumex acetosa and Sedum rosea. Grazing pressure has restricted this association to ledges so there are few natural montane meadows and all populations are above the present limit of woodland (McVean 1964). Quadrats sampled between Meall Buidhe and Beinn Achallader near Bridge of Orchy, together with the grass-rich quadrats from Creag Meagaidh, most closely resemble this association. Athyrium distentifolium var. flexile was frequent, together with Alchemilla alpina, Campanula rotundifolia, Deschampsia cespitosa, Dicranum scoparium, Gymnocarpium dryopteris, Hypnum cupressiforme, Luzula sylvatica, Plagiomnium undulatum, Pleurozium schreberi, and Rumex acetosa which distinguished this group. Cryptogramma crispa was present but less frequent. There was more Dryopteris expansa and Gymnocarpium phegopteris than had been observed elsewhere. Ferns were the major component of the vegetation. The closest NVC community to this (Rodwell 1992) is U16 the Luzula sylvatica–Vaccinium myrtillus tall-herb community in the U16a classification, the Dryopteris dilatata–Dicranum majus subcommunity, but it has close affinities with U18 and many of the species overlap. There is a significant proportion of Deschampsia cespitosa which was most marked in two of the Creag Meagaidh quadrats, one of which had up to 50% cover. McVean (1964) linked the presence of this species to high grazing levels and suggested that it replaced the tall herb association. Odland (1995) stated that the majority of Norwegian A. distentifolium stands are found among the Lactucion alpinae alliance in an association which he considered to be one of the least anthropogenically disturbed habitats. As the nearest approximation to this alpine meadow in Scotland is confined by grazing to cliff ledges, there is a greatly reduced representation of this type of vegetation, although it can be locally extensive. The second of McVean's communities (McVean 1964) is linked to poor soil and low fertility. The NVC classification (Rodwell 1992) related this second type of Cryptogramma crispa–Athyrium distentifolium snowbed vegetation to U18. The constant species are listed as Alchemilla alpina, Athyrium distentifolium, Barbilophozia floerkii, Cladonia bellidiflora. Cryptogramma crispa, Deschampsia cespitosa, D. flexuosa, Galium saxatile, Hylocomium splendens, Hypnum callichroum, Kiaeria starkei, Polytrichum alpinum, Rhytidiadelphus loreus, Rumex acetosa, Saxifraga stellaris and Viola palustris. This community is described as occurring among boulders around the steeper areas behind snowbeds. The Ben Alder and Beinn Eibhinn vegetation with A. distentifolium var. flexile corresponded most closely to U18. This group possibly indicates longer snow lie than the other subdivisions. Ben Alder has large populations of Cryptogramma crispa on the floor of the corrie. The Athyrium tends to grow higher up the side of the corrie but is intermixed with Cryptogramma. Some A. distentifolium also occurs in U11, the Polytrichum sexangulare–Kiaeria starkei snowbed community (Rodwell 1992). Three quadrats from the margin of the scree at Bridge of Orchy together with two from Glen Prosen give an association particularly marked by Anemone nemorosa, Blechnum spicant, Festuca vivipara, Oreopteris limbosperma, Pellia epiphylla, and Viola palustris. This association was again similar to U18, but distinguished areas which were among the earliest to emerge from the snow, but also consistently moist. In view of the species present, this association suggested the Herb-rich birchwood described in Pl. Comm. Scot. with species indicating former woodland. These particular quadrats are in the lower-altitude sites, and the occasional cliff-bound Sorbus aucuparia and the Salix lapponum at Bridge of Orchy and Glen Prosen indicate the potential for montane scrub. In many other countries in which it is found, A. distentifolium grows in woodland extending to the upper limit of the tree line. Examples of these woodland communities are found, for example, in Scandinavian, Central European, Carpathian, and Siberian sites (Davis 1965; Odland 1995; Malyschev 2000; & Dolezal & Strutek 2002), but such divisions cannot be made in Scotland, other than from relict vegetation. In this respect Scottish populations differ from those elsewhere. Many of the open, rocky, acidic Scottish sites with low vegetation cover provide a specific habitat of a type that appears to be less frequent elsewhere. Several authors reported the susceptibility of A. distentifolium to grazing (Moore 1859; Britten 1881; Cowan 1911; Adams 1930). Red deer are present at all the sites. At Ben Alder 50 clumps of each taxon were scored in a traverse across the corrie to assess the percentage of whole clumps which had been eaten. Separate populations were identified at intervals of 30–200 m and the first five clumps encountered were scored. Grazing was very variable depending on the terrain. Accessible plants among stable rocks were often grazed; those among large unstable boulders were not. Of the 20–30% of either taxon which had been grazed, up to 90% of the foliage had been removed (McHaffie 1999). This might represent a significant impact over time as these plants would have to use their reserves to produce new fronds. Overwinter snow provides a specialized habitat which restricts competition (McVean 1958). Vigorous clumps of A. distentifolium shade smaller plants and Gjaerevoll (1950) described the prodigious amounts of litter which suppressed other plant growth. The dead fronds are slow to decay and form dense litter layers. Munther & Fairbrother (1980) found that fern fronds produce a toxic compound which can be leached out of the fronds by rain. The leachate from A. distentifolium helps to have similar effects. In a dense population this could also inhibit the growth of gametophytes near the parents and helps to explain the lack of young plants in large established colonies. As a taller plant, A. distentifolium could shade the smaller var. flexile. Land management has affected the grazing pressure through control of sheep stocking levels and the amount of deer culling. The habitat is less affected than lowland sites, although without grazing A. distentifolium would probably have been in the upper zone of woodland (Pl. Comm. Scot.); the ungrazed remnants among boulder screes occupy a semi-natural environment. Remote location, deep winter snow cover and high altitude give protection from recreational disturbance. The upland habitat is, however, very vulnerable to climate change and enhanced deposition of pollutants. Wilson et al. (1989) found that soils in the range pH 4.2–4.6 are vulnerable to further acidification. Fractionation of ions within a snowbed concentrates the acidic pollutants in the lower layers. Fifty to 80% of the ion load is released in the first 20% of snowmelt to give an acid flush, and bryophytes such as Kiaeria starkei, which occurs in A. distentifolium snowbed vegetation, have been damaged (Woolgrove & Woodin 1996). Melt waters have been found to contain high levels of nitrate and sulphate resulting in a pH as low as 3.2 (Lee et al. 1989). Acidification can lead to slower growth. Hill cloud forms where rising air, which may be polluted, cools at the condensation level. With increasing wind speed and droplet size these pollutants are transferred to plant surfaces (Grace & Unsworth 1988). This gives a greater acid deposition in upland rain as the higher precipitation in montane areas gives an increased input of pollutants. Nitrogen deposition in the Southern Uplands and south-west Scotland is 25–50 kg N ha−1 year −1 compared with 5–10 kg N ha−1 year−1 in lowland Scotland (Cannell et al. 1997) illustrating the higher deposition on high ground. Additional nitrogen could also cause a flush of premature growth and make the plants more vulnerable to frost damage (Lee et al. 1989). Athyrium distentifolium is found in populations varying from a few plants to thousands. Other species, particularly ferns, are present but frequently A. distentifolium is the dominant species. The A. distentifolium var. flexile populations are generally smaller. At Glen Prosen there were fewer than 100 crowns of var. flexile. At Ben Alder there were several hundred clumps of var. flexile, as at Beinn Eibhinn and the main corrie at Bridge of Orchy. Four clumps were found at Creag Meagaidh. In Glen Einich, there was only one large clump and a single crown 1 m away. Other single clumps have also been recorded. There are 17 possible areas where plants of A. distentifolium var. flexile have been recorded, although sometimes only as single plants (McHaffie 1998a). There is a wide range in the reported height of A. distentifolium. Odland (1995) recorded frond sizes from 11 cm to over 150 cm. Schaminée et al. (1992) measured ferns up to 1 m high in the Massif Central, France. Davis (1965) noted southern European A. distentifolium that was 20–50 cm high. The North American A. distentifolium ssp. americanum has fronds up to 80 cm (Cody & Britton 1989). In Norway, Odland (1995) found a correlation between frond size and fertility of A. distentifolium. The percentage of fertility showed a steady increase with frond size and beyond 71 cm all fronds were fully fertile. The tallest fronds which he recorded were over 150 cm. There was decreasing fertility with increasing altitude and in water stressed areas. The highest percentage of fertile fronds was in subalpine rich talus meadow at 500–900 m a.s.l. In very late snow beds the fronds were not fertile (Odland 1991). A sample of Scottish fronds from sites where A. distentifolium var. flexile has not been found gave a mean of 46.7 cm. This mean is slightly larger than the mean for A. distentifolium at any of the sites where var. flexile has been found, the nearest being Bridge of Orchy with a mean of 45.8 cm. This is unusually large for A. distentifolium in var. flexile habitats but the var. flexile here is also larger than anywhere else, at 30.4 cm. The Beinn Eibhinn var. flexile was on average the shortest, 14.6 cm, together with the plants from Glen Prosen, 16.1 cm (McHaffie 1999). Herbarium specimens of A. distentifolium from Continental Europe, Scandinavia and North America (McHaffie 1998a) had the largest mean, 56.9 cm, but the range of 28–139 cm included the size of fronds found in Scotland and does not exclude the possibility of coexistence with A. distentifolium var. flexile-sized plants. In Norway, Odland (1995) measured fronds from 11 cm to 150 cm high covering the full range of A. distentifolium sizes that occur elsewhere, with a potential niche for var. flexile, but although there might be suitable habitats for var. flexile in other countries, it has been found only in Scotland (McHaffie 1999). During the growing season temperatures recorded at the Glen Prosen site did not fall below zero (Table 1). As many of the fern populations are located on steep slopes this gives added protection as cold air will drain away to a lower level. A maximum and minimum thermometer at Bridge of Orchy showed temperatures above zero in the growing season but lower during the winter period (Table 2). The minimum recorded in the period from the end of October to the end of April was −4 °C. This implied that snow would have covered the site for much of the time as a lower temperature would have been recorded otherwise. Plants might be frosted in late spring or early in autumn but there is usually no frost during the short growing season (McVean 1958). Sato & Saki (1981a) used sporophytes of A. distentifolium in freezing experiments and found that they could withstand freezing to −15 °C for one day but were killed at −20 °C. This indicated that over-winter snow cover is necessary to protect from extreme temperatures. Large sporophytes of both taxa in plastic pots survived over winter 1994–95 in a cold frame with temperatures as low as −7 °C. This is more extreme than the lowest over-winter temperature at Bridge of Orchy of −4 °C (Table 2). When gametophytes grown from Scottish spores were frozen the results were variable. Gametophytes of A. distentifolium from Bridge of Orchy regenerated after 1 day and 1 week at −6 °C. Ben Alder A. distentifolium var. flexile gametophytes regenerated after 1 day at −20 °C and 4 weeks at −10 °C. One gametophyte in a set of var. flexile gametophytes from Bridge of Orchy regenerated after 4 weeks at −20 °C. The −10 °C and −20 °C examples could have come from a thickened part of the thallus, which was frequently observed in cultivation (McHaffie 1998a). Snowbeds above the fern beds that melted during the course of the summer were observed to provide seeping moisture at Ben Alder and Meall Buidhe near Bridge of Orchy. The lack of adequate over-winter snow in 1996–97 resulted in plants at Ben Alder suffering from a shortage of melt water. In an investigation into the effects of drought, four sets of gametophytes and four boxes of senescent sporophytes of both taxa were allowed to dry out and given no water for periods from 4 weeks to 16 weeks. After the period of desiccation they were well watered. The gametophytes all died, even after only 4 weeks. The sporophytes recovered well after 4 and 8 weeks, but only three A. distentifolium and two A. distentifolium var. flexile sporophytes recovered after 12 weeks, and one A. distentifolium after 16 weeks. This suggested that the sporophytes can withstand periods of drought better than the gametophytes, but only for a few months (McHaffie 1998a). Gametophytes on a temperature gradient bar were accidentally subjected to high temperatures for 48 h. The temperature at the 25 °C point on the gradient rose to 35 °C. Of the eight dishes of gametophytes, all but three were killed. These surviving three, Glen Doll A. distentifolium, Ben Alder A. distentifolium and Glen Prosen A. distentifolium var. flexile, were badly browned but produced new prothallial growth from the few cells which had survived. On the same occasion, the gametophytes that were normally maintained at approximately 20 °C experienced 29.2 °C and seemed unaffected. This suggested that extreme temperatures could be briefly tolerated in the wild and demonstrated the ability to regenerate from a few surviving cells (McHaffie 1998a). Athyrium distentifolium and A. distentifolium var. flexile fronds arise in irregular shuttlecocks from a central crown. Several authors refer to large branching rhizomes (Gjaerevoll 1950; Odland 1991; Page 1997). Rocks frequently slip downhill over the rhizomes and on excavation the plants are found to originate further up the slope. At Creag Meagaidh, one particular clump of A. distentifolium var. flexile took the form of a dispersed series of 11 crowns within a radius of 50 cm. Isozyme evidence failed to detect any differences suggesting that these plants were all the same clone. As it is so uncommon to find single crowns, this suggested that most populations are composed of long-established plants and that colonization by spores is an infrequent event. A plant of A. distentifolium var. flexile exposed in a rock fall was cut longitudinally. One frond base had a bud with two croziers. This illustrated the potential for offshoots from the rhizome and would also enable new growth in the event of injury to the actual crown, through severe frosting or mechanical damage. At least one root is produced at the base of each frond and this assists in anchoring the rhizome into the mobile scree (McHaffie 1998a). A morphometric analysis of the two taxa gave two distinct groups. Apart from differences in the shape of the fronds a major difference is in the location of the sori. Athyrium distentifolium is less frequently fertile and sori are located at the tip of the frond. Athyrium distentifolium var. flexile is usually fertile and the sori are most dense at the base of the frond. When the sporangia were examined A. distentifolium var. flexile was found to have higher numbers of indurated cells in the annulus than A. distentifolium (McHaffie et al. 2002). Van Cotthem (1970) classified fern stomata into five types; Athyrium stomata correspond to the polocytic type where the stoma is attached to the side of a single cell that is often horse-shoe shaped. The A. distentifolium stomata had a mean length of 49.4 µm (SE 1.07) and a range from 42 µm to 54 µm that was very similar to A. distentifolium var. flexile 48.8 µm (SE 1.05) with a range from 44 µm to 54 µm (McHaffie 1998a). Stomatal frequency scores on individual plants were very variable. The mean basal counts of the Glen Prosen A. distentifolium ranged from 27 mm−2 to 86 mm−2 (mean 54.7, SE 6.1) and indicated how difficult it is to give an accurate generalized mean. A. distentifolium var. flexile from the same site had a mean range from 27 to 56 (Mean 43.5, SE 3.0). The position of a frond within the clump could give a greater degree of shading and many ferns, but not all, grew among the rocks. Athyrium distentifolium var. flexile, as a smaller plant, was more likely to be sheltered by rocks and sometimes only the tips of the frond were exposed. The horizontal habit of var. flexile would also shelter the underside more than an upright frond. Although there appears to be a difference in the stomatal frequency between taxa this is the inevitable result of the growth form of var. flexile and plants of A. distentifolium growing in similar situations can range down to these scores. Ludlow & Wolf (1975) found fern species that always grow in the shade have higher chlorophyll content than ferns from sunny habitats, compensating for the lower photosynthetic rates. There is a marked colour difference between A. distentifolium, which tends to be more yellow-green, and A. distentifolium var. flexile which is usually a blue-green, indicating it is more a shade fern. This colour difference is maintained in cultivation where both taxa receive the same light levels. Nespiak (1953) found no mycorrhiza in Athyrium alpestre (A. distentifolium) in a Polish Oxyrieto-Saxifragetum association, but this community suggests a high nutrient environment where mycorrhiza might be less beneficial (Read et al. 1976). Dominik & Nespiak (1953) recorded arbuscular mycorrhizas from A. distentifolium in Pinus mugo and Adenostyletum-alliariae associations. Dominik et al. (1954) also noted A. distentifolium roots colonized by arbuscular mycorrhizas in a Picetum excelsae myrtilletosum association. Samples of both taxa were examined from several sites in Scotland for arbuscular mycorrhiza and all showed some colonization ranging from 2% to 74% root length colonized. There was some evidence for increasing levels of colonization in the summer months and in less fertile soil (McHaffie 1998a). Reproduction must be infrequent from spores as most plants have a multiple rhizome and gametophytes are rarely found. The plants appear to be long-lived and spread by budding sideways. It was found that when grown in conditions of high humidity in a glasshouse, some plants of A. distentifolium var. flexile from Creag Meagaidh and a site near Bridge of Orchy produced bulbils. These were usually confined to the axils of the lowest pair of pinnae and soon extended roots (McHaffie 1998b). This has not been observed in the field. Manton (1950) counted the chromosomes of A. distentifolium, A. distentifolium var. flexile and A. filix-femina and for all of them found 2n = 80. This was confirmed by McHaffie (1998a). The response to drought and freezing has already been described in V(C). Athyrium distentifolium and A. distentifolium var. flexile were found to behave differently in response to nutrients. Both gametophytes and sporophytes were grown at different nutrient levels (McHaffie et al. 2001). Under low-nutrient conditions, especially those with a pH of 3.8, or with a calcium, phosphorus or potassium deficiency, gametophytes of A. distentifolium var. flexile grew faster than A. distentifolium gametophytes. Similarly, sporophytes grown at different levels of nutrient showed different responses. Athyrium distentifolium required high levels of nutrient to be even partially fertile, while var. flexile was fertile with fewer nutrients (McHaffie et al. 2001). Where the two taxa grow together in the wild A. distentifolium is typically taller than var. flexile but frequently is not fertile. Only in areas with a high pH does A. distentifolium attain the full height, often in excess of 1 m, and become fully fertile. Where both taxa grew together the pH was low, ranging from 3.3 to 4.5 (McHaffie 1998a). It appears that A. distentifolium var. flexile is found only where the competition from A. distentifolium is reduced by the low-nutrient environment. Frond samples for allozyme electrophoresis were collected from 12 Scottish sites and sent to the research team at the Natural History Museum in London. The Scottish material included six sites where both taxa were present and six sites where A. distentifolium var. flexile had never been recorded. A few samples of A. filix-femina were also included. Samples of A. distentifolium were also sent from the Pyrenees in France, Southern Switzerland and Erzgebirge in Germany making a total of 23 populations with over 600 samples. Allozyme electrophoresis was used to test the species identity of A. distentifolium var. flexile in relation to A. distentifolium. Thirteen enzyme systems with 21 loci could be analysed and of these allelic variation was recorded for nine loci. There were no alleles specific to A. distentifolium var. flexile and there was more variation in the allele frequency between localities than between the two taxa within each locality. This showed that populations in separate corries have been isolated for some time. A cluster analysis of all the populations included in the study indicated three groupings. Plants from the Pyrenees were very distinct from all the others. All the Scottish populations with both A. distentifolium and var. flexile had a similar allele frequency together with a population with a doubtful old record of var. flexile and another population with no previous record. The final grouping included the remaining Scottish populations of A. distentifolium and the populations from Germany and Switzerland (McHaffie 1998a). Athyrium distentifolium was also used as part of a study for the development of EST–SSRs using plant material from around the northern hemisphere. Polymorphic markers were found, suitable for biodiversity research (Woodhead et al. 2003; Squirrell et al. 2004) and a clear separation was seen between European plants and those collected in North America (Woodhead et al. 2005). In Norway, where the snow could last until August, Odland (1995) found that A. distentifolium at 750 m a.s.l. usually commenced growth in June Frond expansion did not start until the soil temperatures at a depth of 5 cm reached 6–7 °C. It then took 24–27 days for the fronds to expand fully. This was faster than Oreopteris limbosperma or Matteucia struthiopteris which grew nearby (Odland 1991). In
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