Biosystematics of some species of epilobium

Abstract

Most European species of Epilobium are known to hybridize, and many occupy overlapping habitat*. All have the same chromosome number (2n = 36) and their chromosomes are similar. The main aims of the thesis have been to inquire into isolating mechanisms in the genus and to study systanatic relationships between its members. 16 species have been used, H European and two from New Zealand. Herbarium records indicate that, in Britain, interspecific hybrids are relatively rare. Internal isolating mechanisms which have been studied include (a) slow growth of pollen-tubes in hybrid crosses, (b) post-fertilisation failure of the hybrid seed, (c) failure of hybrid seed to germinate, (d) weakness of hybrids, and (e) sterility of hybrids, both F1 and F2. The fact that many of the species are regularly self-pollinated has also an important bearing on isolation, and helps to account for the relative scarcity of interspecific hybrids in nature as revealed by herbarium studies. The hybridization experiments have shown that E.angustifolium and E.fleischeri. which belong to the Section Chamaenerlon, are a separate breeding group distinct from Sect. Lysimachion. This supports the separation of the two sections of the genus made on morphological grounds. The view that Ghamaenerion be treated as a distinct genus is not supported by the evidence derived from the present work. Separation of Lvsimachion into two groups. Division Schizostiema and Division Svnstigaa. on the basis of whether the stigma is 4-lobed or entire, is artificial and is not justified either by hybridization experiments or on morphological grounds. The two New Zealand species do appear to be morphologically distinct from the European species studied j one of them is able to hybridize with the European species, and the other not.