Floral evolution in the Hamamelididae. II. Interpretative floral morphology of the Amentiferae

In this second paper of the series, the floral morphology of apetalous orders most probably to be included in the Hamamelididae, and historically referred to by the name of “Amentiferae”, is discussed. Various traits can be discerned, such as the advent of filaments (not found, or only present in statu nascendi, in Juglandaceae, Balanops, and some other taxa), the prevalence of either free or adnate anthoid members, the alternatives of a condensation (brachyblasty) of gonoclads and a more macroblastic organisation of the gonocladial floral units, and of a bilateral against a radial symmetry of the anthoid members, and, finally, unequal rates of oligomerisation and depauperisation of the various subordinate parts of the ancestral anthocorms. The prevailing trends of advancement more or less clearly distinguish the various orders, but do not stand in the way of the phylogenetic origin of their reproductive regions from the same macroblastic, basically unisexual, and holomonandrial archetypic anthocorm. A characteristic feature shared with the Hamamelidales is the almost complete lack of a tendency towards a brachyblastic modification of the anthocormoids (i.e., towards the development of holanthocormous, “true” flowers), a trait not found in any other major group of Dicots. The functional reproductive units are usually anthoidal, but anthoids sometimes became reduced to pseudomonomerous units. The available evidence strongly suggests an independent origin of the hamamelidid assembly since at least the Middle Cretaceous, and renders an early divergence into several parallel lineages (some leading to amentiferous, and some to hamamelidalean taxa) rather plausible. Contrary to current belief, the Amentiferae do not constitute an artificial group. The floral morphology of the different forms is more or less diverse, but the basic traits of floral evolution are essentially similar. The relationships of the relict group of the Balanopsidales (= Balanopales) are extremely important if not crucial because this taxon is anthomorphologically “at the cross-roads” of the evolutionary lineage of the Juglandales on the one hand, and that of the Betulales and Fagales (and Casuarinales?) on the other. These taxa, and presumably also the extremely depauperated Leitneriaceae are thus linked together and must all be included in the Hamamelididae.