Floral evolution in the Hamamelididae. III. Hamamelidales and associated gropus including Urticales, and final conclusions

The final paper of this series deals with the interpretative floral morphology of the Hamamelidales and some associated groups including the Urticales (which need not be closely related). The rather varied architecture of the reproductive structures of the Hamamelidaceae, which has been controversial when attempts were made to explain it in terms of the classical floral theory, can easily be understood if the floral region is interpreted as anthoidal in nature, i.e., as derived from gonoclads which are in this family sometimes macroblastic and sometimes condensed into a sometimes “petaliferous” (and zoophilous) anthoidal reproductive unit (such units are normally coaxially borne because they are derived from partial anthocorms). The taxa with brachyblastic anthoids (the petaliferous Hamamelidoideae) are relatively speaking the most derived, and the more manifestly macroblastic and unisexual ones (apetalous Hamamelidoideae, Symingtonia, Liquidambar, Altingia, etc.) more archaeic, which conclusion is quite at variance with current views. The Amentiferae and Platanaceae are not descendants of brachyblastic, ambisexual and phaneranthous hamamelidids either. The phylogenetic history of the possibly related Urticales and of some taxa commonly included in the Hamamelididae such as Trochodendrales, Cercidiphyllum, Eucommia, and Euptelea is very similar to that of the Amentiferae and Hamamelidales, and even if they are not related, their reproductive units are mostly or perhaps consistently anthoidal in nature. The floral morphology of other, unrelated “monochlamydeous” taxa is also interpretable in terms of anthoids, which in turn facilitates the acceptance of a close relationship between these forms and groups with (partly) holanthocormous flowers (compare Salicaceae – Flacourtiaceae, Euphorbiaceae – Malvales). The conclusions emanating from the deductions made in the present series of contributions indicate a much more pleiophyletic evolution of the Flowering Plants than is generally assumed and also a frequent, and repeated, incidence of parallel trends in floral evolution. The prevalence of certain traits may nevertheless characterise a major taxon, and the present author is of the opinion that the exceptional, complete lack of brachyblasty of the anthocormoids is a distinguishing feature of the hamamelidid assembly. (The extreme reduction of female anthocormoids in some amentiferous forms – Fagales, etc. – is a special trait not comparable with brachyblasty in other groups of Dicots). Finally, some aspects of the evolution and classification of the Hamamelididae are discussed and summarised, their independent evolution as a group and the primarily of apetalous (aphananthous) diclinous forms being emphasised.