Vitaceae (Grape family)

The family includes 12 genera and about 700 species, occurring in temperate, subtropical and tropical zones of both hemispheres. The largest genus is Cissus with its more than 350 species. Vitaceae are small trees, erect shrubs or, more often, woody lianas.

Leaves are usually alternate, very rarely opposite, very variable in shape, more often 3-5-palmately divided or lobed, less often pinnately or palmately compound, trifoliolate or twice-trifoliolate, or finally simple. Sometimes closely related species exhibit very different leaves, and at times even on the same plant one can find simple leaves (on the lower parts of the stems) and divided leaves (higher up). Flowers are usually in terminal inflorescences, typically small, greenish, very rarely reddish or golden-yellow, actinomorphic, bisexual, polygamo-dioecious or dioecious, 5- or 4-merous. The calyx is generally weakly developed, sometimes reduced to a calyculus-like thickening at the base of the corolla. Petals in number (3)5(6-7), free or fused by their bases into a tube or by their tips. In the latter case the petals fall off as a whole in the form of a cap, supported from below by stamens that straighten. At the base of the ovary a glandular nectar disk often develops. Stamens (3)4-5, attached to the base of the nectar disk. The gynoecium consists of 2 carpels; the style is simple, usually with a disc-shaped or capitate, less often 4-lobed or 4-parted stigma; the ovary is superior or more or less united with the disk, 2-loculed, with 1-2 ovules in each locule. The fruit is a fleshy (or almost dry) berry with 1-4 seeds, with a hard seed coat; seeds with a small embryo surrounded by abundant and often ruminate endosperm.

Most Vitaceae inhabit moist and warm, especially primary forests, where they often make up a significant part of the so-called liana flora. However, in the tropical zone some representatives of this family extend high into the mountains. For example, Parthenocissus himalayana grows in Sikkim (Eastern Himalaya) at an altitude of 3300 m. On the other hand, there are species associated with arid regions (steppes, savannas and even deserts) of southern Africa and South America.

Root modifications deserve attention, namely the development of aerial roots in some representatives of the Vitaceae. For instance, in Cissus gongylodes the aerial roots are cylindrical, smooth, red, unbranched, reaching several meters in length; and in C. quadrangula parts of the aerial roots that are buried in the soil develop root tubers reaching 20 mm or more in diameter, which can be related to the arid climate in the habitats of these species. Aerial roots develop from the nodes of the stem on their downward-facing side; upon reaching the ground they penetrate it, but then grow more slowly. On the roots of some Vitaceae in Malaya the famous Rafflesia arnoldii often parasitizes. The biology of flowering has been studied only for a few species of the temperate zone; for plants of the southern zones (tropical and subtropical) it is very poorly studied and in many cases remains unknown. Nevertheless, it has been established that Vitaceae are pollinated by insects and by wind. In several cultivars of cultivated grape, where flower pollination has been studied in some detail, cases of self-pollination have been recorded, sometimes even in unopened flowers (cleistogamy).