The developmental morphology of Parthenocissus tricuspidata (Boston Ivy) and Parthenocissus quinquefolia (Virginia Creeper) was compared. The two species are distinguished from their relatives in the Vitaceae (the Grape Family) by their adhesive tendrils. Epi-illumination microscopy and scanning electron microscopy have been used to observe developmental stages of a tendril from inception to maturation. The intent of this study is that the addition of comparative developmental data will help in determining the phylogeny of the Vitaceae. The shoot apex produces two tendril primordia at two nodes of a three-node cycle. Tendril primordia arise as follows: (1) a lower tendril primordium, opposite of a leaf, arises high upon the flank of the apex. (2) The upper tendril primordium, opposite of a leaf, arises above the leaf of the lower tendril node, low on the flank of the apex. The development of the tendril as in the main shoot apex is monopodial. The apical meristem of the tendril produces several smaller leaf opposed primordia that develop into tendril branches. Tendrils of P. quinquefolia generally develop 7 lateral branches whereas tendrils of P. tricuspidata generally develop 9 lateral branches. Mature tendril tips always bear adhesive pads: pads of P. tricuspidata seem to arise precociously as spherical swellings at the branch tips while pads of P. quinquefolia only arise during later development. When an adhesive pad contacts certain substrates, cells of the epidermal surface grow and divide which produces a large surface area. A comparison of tendrils in these two species provides evidence for ancestral sympodial growth and a consistent ontogeny of tendrils in the Vitaceae.

Key words: anatomy, development, morphology, Parthenocissus, tendrils, Vitaceae