Origin of the Trimerous Perianth

Abstract

THE trimerous perianth being one of the characteristic features of the monocotyledons, its origin is an important problem of floral morphology. Salisbury1, from detailed studies of meristic variations among the floral parts of the Ranunculaceæ and Helobiales, has come to the conclusion that trimery is really the most primitive condition among the angiospermous flowers. The pentamerous whorl, according to him, has evolved from two trimerous whorls by the fusion of one member of the outer and one member of the inner whorl. A study of the vascular anatomy of the male flowers of Myristica fragrans Houtten, Fam. Myristicaceæ, however, leads to a quite contrary view. This family is phylogenetically not far removed from the Ranunculaceæ and is usually included among the Ranales. Its diœcious flowers possess a tubular or campanulate perianth, which divides above generally into three lobes. The serial transverse sections of the male flowers of Myristica fragrans show that the trimerous perianth is supplied by ten vascular traces (Fig. 1). Such a vascular supply is clearly of a pentamerous whorl.