Studies in the Alismataceae. II. Inflorescences of Alismataceae

Abstract

Aspects of morphology and development of alismataceous inflorescences have been studied. The inflorescences are always terminal, and transition of the vegetative meristem to the reproductive state is accompanied by the formation of a large vegetative bud in the axil of the last foliage leaf formed before transition. The inflorescences of the family are almost all built on a common plan with bracts in false whorls of 3 on the main axis (and branches when present). The basic structure subtended by the bracts is a bostrycoid complex of flowers (or branches and flowers in the lower parts of some large inflorescences). Modifications of various kinds occur in different cases: the bostryx may be reduced to a single flower; vegetative buds may occur in flower positions in bostryces; a single vegetative bud may replace a whole bostryx in inflorescences much modified in relation to vegetative reproduction. Development of bostrycoid complexes is dependent on formation of buds in prophyll axils and does not occur where prophylls cannot be detected. Some species have inflorescences in which a diversity of lateral structures is associated with each pseudowhorl of bracts and these are termed heterogeneous inflorescences, in contradistinction to homogeneous inflorescences, in which all the lateral structures in a pseudowhorl are of the same kind. Main and branch axes of an inflorescence normally terminate in a flower. Exceptions occur in some (possibly advanced) types in which inflorescence growth is terminated by abortion, and in specialized inflorescences modified in relation to vegetative reproduction which have unlimited growth. The data presented are discussed from systematic, evolutionary, and morphogenetic points of view.