Shoot Development and Evolution in Pistia stratiotes (Araceae)

Abstract

The development of the shoot of Pistia has never been well understood, as is evident by the conflicting interpretations that have been reported in the past. This most likely results from the extremely condensed stem, nonsheathing mature foliage leaves, misinterpretation of squamule(s) at the base of the inflorescence, and lack of three‐dimensional studies, all of which obscure the interpretation of shoot appendages. Pistia has a sympodial shoot system in which each diphyllous sympodial unit terminates with the production of an inflorescence. The primary bud of each prophyll develops precociously via a bifurcation of the shoot apex, continuing the growth of the shoot. Three supernumerary buds, which may enhance the plant's high vegetative reproductive capacity, develop in the axil of each prophyll, whereas no buds develop in the foliage leaf axil. The secondary bud develops into a stolon; the tertiary and quaternary buds appear to remain dormant. Understanding shoot development in flowering shoots has provided an explanation for the architecture of vegetative Pistia shoots. These shoots are a series of repeating foliage leaves and reduced leaves that appear to be sterile (monopodized) shoots and have likely evolved from the sympodial flowering shoot system.