Shoot development and evolution in Pistia stratiotes (Araceae)

The development of the shoot of Pistia has never been well understood, as i s evident by the conflicting interpretations that have been reported in the past. This most likely results from the extremely condensed stem, nonsheat hing mature foliage leaves, misinterpretation of squamule(s) at the base of the inflorescence, and lack of three-dimensional studies, all of which obs cure the interpretation of shoot appendages. Pistia has a sympodial shoot s ystem in which each diphyllous sympodial unit terminates with the productio n of an inflorescence. The primary bud of each prophyll develops precocious ly via a bifurcation of the shoot apex, continuing the growth of the shoot. Three supernumerary buds, which may enhance the plant's high vegetative re productive capacity, develop in the axil of each prophyll, whereas no buds develop in the foliage leaf axil. The secondary bud develops into a stolen; the tertiary and quaternary buds appear to remain dormant. Understanding s hoot development in flowering shoots has provided an explanation for the ar chitecture of vegetative Pistia shoots. These shoots are a series of repeat ing foliage leaves and reduced leaves that appear to be sterile (monopodize d) shoots and have likely evolved from the sympodial flowering shoot system .