The inflorescence morphology and systematics of Aulax (Proteaceae)

Abstract

Three species are recognized in a revision of the functionally dioecious genus Aulax Berg. (Proteaceae), endemic to the south-western and southern Cape Province. Aulax displays marked sexual dimorphism in the inflorescences. The male inflorescences are lax panicles in A. pallasia Stapf and A. umbellata (Thunb.) R.Br. and a lax raceme in A. cancellata (L.) Druce. The female inflorescence is a cupule-like structure at anthesis, becoming closed and serotinous in A. umbellata and A. cancellata but remaining partly open and non-serotinous in A. pallasia. It is suggested that the female inflorescence is derived from a monoecious panicle by the fusion and incurving of the axillary inflorescence branches and associated flowers around a central raceme of female flowers. The inflorescence of Aulax pallasia represents the most primitive surviving stage in which the widely splayed axillary inflorescence branches bear female as well as pedicellate and pedunculate sterile male flowers. Aulax umbellata is further reduced with pedicellate (no longer pedunculate) sterile male flowers occasionally produced on the axillary inflorescence branches which are now fused into incurved woody fascicles, smooth proximally but with a comb of subulate points of tissue distally. This comb is formed from sterile flowers and associated bracts of the fused axillary inflorescence branches. The most reduced and most serotinous stage is in A. cancellata where the axillary inflorescence branches are reduced to smooth incurved woody fascicles with an apical comb but with no trace at all of male or female flowers and their associated axes on the fascicles. It is suggested that the evolution of serotiny in the above reduction series has resulted from selection for the protection of the fruits from fire.