Novel variation in the floral development of two species of Parthenocissus.

This study compares the development of the inflorescences and flowers of Parthenocissus quinquefolia (Virginia creeper) and Parthenocissus tricuspidata (Boston ivy). The development of the reproductive shoots is described from inception to maturity using epi-illumination and scanning electron microscopy. In both species, the shoot apex initiates inflorescence primordia low on the apical flank. An inflorescence primordium produces several bract-opposed branches, which in early development resembles the main shoot. As inflorescence development continues, branch primordia initiate as increasingly larger portions than the inflorescence apical meristem. By late development, branch primordia initiate as larger portions than the apex, which is a process that has been observed in other vitaceous inflorescences. With respect to initiation and early development, the Parthenocissus inflorescence is very similar to the tendril, which has been previously studied; these two organs have never been described to be so similar, and their likeness to the shoot, in early development, provides an idea as to how they may have arisen. An inflorescence branch terminates as a dichasium, which is formed by two nearly simultaneous branching events. Parthenocissus tricuspidata flowers develop a more robust gynoecial disc and stigma than in the P. quinquefolia flower; but the calyx is ring-like in the former and cup-like in the latter. Contrary to the previous assumption that there axe no differences in reproductive biology within genera of the Vitaceae, this study has clearly demonstrated variation between two species of Parthenocissus. [ABSTRACT FROM AUTHOR]