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Cytotaxonomical atlas of the pteridophyta , Cytotaxonomical atlas of the pteridophyta , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

The quillworts, or the genus Isoetes, are among those fernallies that are in great need of cytotaxonomical and experimental revision. Though Linnaeus (1753) recognized only a single species, later authors have generously described new species of this group even from very limited collections, with the result that Reed (1953) recognized over 610 names, representing, in the view of Lawrence (1951), only about 60 species. It is evident from the studies by Iversen (1928a,b) that several of the characters used for the separation of many of these taxa are taxonomically doubtful, and there is reason to believe that a few are only occasional edaphic modifications. Some are evidently good races which ought to be treated at the varietal or subspecific level, whereas still others are undoubtedly very good species. Distinguishing four sections on the basis of surface characters of the megaspores, as proposed by Pfeiffer (1922), may be apparent rather than natural, but the morphological characters used in separating the monotypic genus Stylites (Amstutz, 1957) seem to be genuine. Though the distinction and relationship of Isoetaceae to other ferns and fern-allies have been widely dis

Although the genus Galium is one of tlhe larger genera of the higher plants, including more than 250 species (cf. Schumann, 1891; Willis, 1949) distributed throughout both hemispheres, it does not as yet seem to have found its present day monographer. Several of its critical taxa have been studied separately by different botanists. However, in recent manuals, the same author may treat some of the species of the genus in the sense of the splitter, while others are considered from the point of view of the lumper (cf. Fernald, 1950; Hulten, 1949). These differences in opinion about the various taxa of the genus are certainly due only to the fact that most of the subgroups already described are found to differ in but slight technical characters, and, as most of the species are small, their minute morphological differences are not always readily observed. According to Schumann (1891), the genus should be naturally grouped into at least fourteen different sections, some of which are divided into subgroups. Each of these groups is morphologically very distinct, while only a few minor characters are found to be sufficient to distinguish the species of each section or subsection. Nevertheless, the rather morphologically related species are found to have a distinct area of distribution, hybrids between them are rare or even absent, and, in cases where they have been studied from the cytogenetical points of view, species even morphologically very closely related or types previously known as varieties by taxonomists, have been found to have a strong barrier of hybrid sterility or incompatibility based on differences in the nunber or structure of tlheir chromosomes (cf. Homeyer, 1935; Fagerlind, 1937; Ehrendorfer, 1949, 1951; Poucques, 1949). The perennial section Platygalium DC. includes about ten species differing iti a few technical characters only. Some of these certainly are valid species and include but one ecospecies in the sense of the modern biosystematists (cf. Turesson, 1922, 1925, 1930, 1938; Clausen, Keck, and Hiesey, 1940, 1945), while the morphological as well as the geographical variability of some of the others indicate that they are collective species which might be given a more correct taxonomical status on the basis of cytotaxonomical or genecological analysis. One of these species is the so-called Northern Bedstraw, or the collective species Gdlium boreale of all recent manuals covering different parts of the northern hemisphere. The species Galium boreale was originally described by Linnaeus (1753) from northern Europe ("Habitat in Europae borealis pratis"). In that outstanding "Atlas of the Distribution of Vascular Plants in N.W. Europe," Hulten (1950) classifies it as one of the boreal-circumpolar plants lacking large gaps in their area. Notwithstanding this schematical classification, the species shows a very clear gap in its distribution from southern Quebec to Iceland (cf. B6cher, 1938; Fernald, 1950; Ostenfeld, 1926; Raymond, 1950; Scoggan, 1950), and the ecological requirements of the North American and European populations seem to be somewhat different. In Scandinavia (cf. Hulten, 1950; Lid, 1944; Nordhagen, 1940; Dahl, 1934; Kotilainen, 1951), the British Isles (cf. Druce, 1930; Webb, 1943), as well as in the Faeroes (cf. Rasmussen, 1936) and Iceland (cf. L6ve, 1945; Stefansson & Steindorsson, 1948) it is met with in alpine as well as rather maritime and inland subarctic 88