Flowers and inflorescences of the “Amentiferae”

The floral and inflorescence morphology of the major genera of the Myricaceae, Betulaceae (including Corylaceae), Fagaceae, Leitneriaceae, and Juglandaceae are reviewed. Major problems in interpretation of morphology are examined in the light of various comparative morphological studies as well as ontogenetic and vascular anatomical studies. Basically similar phenomena associated with miniaturization of the partial inflorescence have led to superficially similar morphological patterns. The partial inflorescences in the various families, in spite of their reduced size, can be adequately analyzed in most cases on the basis of the bract-branch relationship. The highly modified morphology of the floret is clarified by the application of the general tenets of the leaf-stem relationship in the frame of reference of the minute absolute size of the floret. Numerous problems remain to be attacked. The total and partial inflorescences and the florets of the Myricaceae, Betulaceae, Fagaceae, Leitneriaceae and Juglandaceae are reviewed in terms of external morphology, vascular anatomy and ontogeny as reported in the more objective literature on the subject. The total inflorescences in these families range from the complex, androgynous panicles of stiff spikes of such genera asCastanopsis to the condensed, bud-like pistillate spikes of some Myricaceae andCorylus on the one hand, to the simple staminate floret in the axil of the foliage leaf in some species ofNothofagus on the other. In many species of these families the inflorescence is the apparently simple spike with a flaccid axis, the ament, but so often is this not the case that the designation “Amentiferae” for this artificial assemblage must be considered a misnomer. Whether the total inflorescences are composed of racemose or cymose partial inflorescences is a question not completely answered in all the families. In the Betulaceae the partial inflorescence has long been taken to be a cymule. But, a re-interpretation of the vascular anatomy suggests the alternative that the most distal floret in a short raceme has overtopped the axis of the partial inflorescence thus producing a pseudo-cymule. This is similar to a recent interpretation of the staminate partial inflorescence ofMyrica esculenta, where the individual floret is composed of a single stamen. The partial inflorescence in the more reduced species ofMyrica is thus a pseudanthium. Recent ontogenetic studies in the Betulaceae dramatically corroborate the earlier interpretation, based on vascular anatomy, that the staminate partial inflorescence ofOstrya is three-flowered. On similar grounds it has recently been shown that the spiny “involucre” of pistillateComptonia is composed of tertiary bracts. The structure of the staminate partial inflorescences in the Fagaceae seems reasonably clear except in certain species ofNothofagus where it may well be a synanthium, although the alternative of chorisis exists. The interpretation of the pistillate partial inflorescence inLeitneria requires re-study; the unvascularized tepal-like structures subtending the ovary have been alternatively treated as bracts -an ontogenetic study is badly needed. The organization of the staminate partial inflorescence of the Juglandaceae remains equivocal, although recent ontogenetic work on one species ofJuglans shows that the primordia of the secondary bracts are readily distinguished from tepal primordia, although at anthesis they are very similar. At present the number of florets in the partial inflorescence of the Juglandaceae remains an open question in spite of a fragmentary study of the vascular system. The cupule ofLithocarpus andQuercus continues to present a major morphological problem. The valves of the husk in other genera of the Fagaceae seem, on the basis of the vascular anatomy and some ontogenetic information, to be axes of the ultimate order of branching. A thorough study of these complex structures is needed. Staminate florets which are set off by tepals are readily identified with the reservation that those of some species ofNothofagus and ofJuglans, for instance, may be more complex than they seem. The absence of tepals creates major difficulties which have been resolved in some instances by the study of the vascular anatomy and/or ontogeny. But many problems remain. The pistillate floret seems clearly delimited in the various families. There continues to be the usual conflict concerning the proper interpretation of the wall of the inferior ovary, whether on the basis of ontogeny it should be considered cauline or on the basis of the vascular anatomy it is to be considered appendicular. Oddly enough there are also diametrically opposed interpretations of placentation -is it axile or parietal in one and the same species. This perhaps results from a conceptual conflict. The basal ovule, as in the Myricaceae, or even the ovules perched on a partial septum, as in the Juglandaceae, are similarly much discussed. The ontogenists tend to agree that such ovules are cauline, while the anatomists find that the complex vascular system is not that of a stele. There is a multitude of discrepancies, as yet, in observations, and even when there is mutually accepted fact, there are often conflicting interpretations. Above all, there is a massive lack of knowledge of the vascular anatomy and ontogeny of these miniature and modified flowers and inflorescences.