. Bulletin of the British Museum (Natural History) Botany. STUDIES IN THE GENUS HYPERICUMS. (GUTTIFERAE) 67. Fig. 2 Affinities of sections of//r/w/t urn, slightly modified from Robson (1977a : figs 1,2). the complete geographical segration of the two taxa and the fact that united styles recur only in advanced species of sect. Ascyreia ( H. monogynum) allow one to recognise them as sections. The forked line to sects 24 and 25 indicates that the relative advancement of these sections is not clear. Thus, although the vegetative parts in sect. 24. Heterophylla (H. hetero- phyllum) are more adv
. Bulletin of the British Museum (Natural History) Botany. STUDIES IN THE GENUS HYPERICUMS. (GUTTIFERAE) 67. Fig. 2 Affinities of sections of//r/w/t urn, slightly modified from Robson (1977a : figs 1,2). the complete geographical segration of the two taxa and the fact that united styles recur only in advanced species of sect. Ascyreia ( H. monogynum) allow one to recognise them as sections. The forked line to sects 24 and 25 indicates that the relative advancement of these sections is not clear. Thus, although the vegetative parts in sect. 24. Heterophylla (H. hetero- phyllum) are more advanced ( in having the leaf-differentiation from which it gets its name) and its distribution suggests a derived relative position, the flowers are homostylous, whereas in sect. 25. Adenotrias they are heterostylous. The evolutionary diagrams of sections ( Fig. 5) have been produced by stages, in a way rather similar to building up a jigsaw- puzzle picture. Certain primitive/advanced relationships are usually obvious; but, even if the trend directions in them are not clear at first, small separate 'pieces' of the diagram can be constructed on the basis of overall similarity. In theory, the whole diagram could be produced in this way (Fig. 4); but in practice it and others like it have resulted from a con- sideration of trends at an early stage. Thus its conversion into an evolutionary hypothesis by the insertion of (i) directional indications and (ii) the 'nearest neighbour' or 'sister group' to the whole section (Fig. 5) was not an entirely separate process. The two stages, however, show some similarity to the ground plan/divergence diagrams produced by Wagner (1952a, b) and subsequently elaborated by him and others ( Wagner, 1969; Farris, 1970). The first-stage (interrelationship) diagram corresponds to the 'Wagner network' and the second (cladal) to the 'Wagner tree' (Nelson & Van Horn, 1976), but a numerical basis is lacking (for the reason stated above); and
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