Virginia creepers
Dramatic images of East Asian 'ghost villages', where deserted houses and streets are covered with luxuriant vegetation, reveal the remarkable abilities of plants to recolonise areas abandoned by humans. One of the principal genera in such natural 're-greening' phenomena is Parthenocissus. The generic name Parthenocissus is a French common name, vigne vierge (virgin ivy), rendered into botanical Greek.
The natural abilities of Parthenocissus species to colonise areas rapidly, have made them serious invasives in some regions, but attractive horticultural species in European and North American gardens. For example, Virginia creeper (Parthenocissus quinquefolia), Himalayan ivy (Parthenocissus semicordata) and Boston ivy (Parthenocissus tricuspidata) are widely used as climbing ornamentals. They make their presences known most obviously in the spring with their new green leaves, or in the autumn with their dramatic changes in leaf colour.
Approximately 12 Parthenocissus species are distributed between Asia (nine species) and North and Central America (three species). All species are deciduous, woody climbers. Most species are found in temperate regions, although one species (Parthenocissus heterophylla) is found in tropical Asia. This species is thought to have evolved from its temperate relatives.
Parthenocissus species have palm-shaped leaves often with different numbers of leaflets, and tendrils with more than two branches. Each tendril branch usually ends in a flat, adhesive disc that sticks the plant to any structures, living or dead, over which it climbs. In Boston ivy, growing shoots scan potential climbing substrates. The attachment pads are differentiated into central and peripheral regions, which appear to have different functions. The peripheral region probably secretes adhesive ?uid. Under the attachment pad irregularities in surface texture are ?lled either by pad cells growing into any cavities or by the adhesive ?uid secreted by the pad.
Until recently, the genus Parthenocissus was more broadly defined to include species with two tendril branches. These species were separated into the small genus Yu; a decision subsequently supported by DNA-based analyses.
Traditionally, groupings of species within the genus Parthenocissus have been based on either their geographic distribution (Asia versus Americas) or obvious morphological features such as the numbers and shapes of leaflets on each leaf. DNA data identify two major groups in Parthenocissus corresponding to the Asian and the American species. Moreover, it is estimated that these groups separated from each other about 20 million years ago. In contrast, splitting up the genus based on leaflet number is not supported by the DNA data.
Further reading
Nie Z-L et al. 2010. Molecular phylogeny and biogeographic diversification of Parthenocissus (Vitaceae) disjunct between Asia and North America. American Journal of Botany 97: 1342-1353.
Steinbrecher T et al. 2011. Structural development and morphology of the attachment system of Parthenocissus tricuspidata. International Journal of Plant Sciences 172: 1120-1129.
Stephen Harris