For our summer newsletter, we are traveling to the Hilgard fence, about 100 meters north of the southern gate at Hilgard and LeConte. Here, growing on and through the chain links, is Tetrastigma voinierianum (Pierre ex. Nichols. & Mottet) Gagnep., known in the trade as chestnut vine or lizard plant. This liana of the grape family (Vitaceae), from tropical forests in Laos, has long internodes (to 20 cm) and alternately arranged, palmately compound leaves. Next to the base of the petiole is a pair of leaf-like stipules, attached to the stem (persistent intrapetiolar stipules). Five downward-oriented (pendulous) leaflets hide the lower leaf surface from view. Tendrils--sometimes 25 cm in length--arise directly opposite each leaf, forming bridges within the plant and coiling around the fence wires. Our specimen is spreading out of control, extending ten meters or more north and south from the plant's base, and enveloping other dicotyledons and conifers in its path.
What first amazes onlookers is the vibrantly colored velveteen of the stems, unfurled leaves, and tendrils--almost the color of a red fox. The soft, dense coat of plant hairs (trichomes) is red-orange above and whitish underneath, and may be described as velutinous-tomentose, much like animal fur. A trichome is straight and nonglandular, consisting of a single chain of cells. Each of the five obovate leaflets is covered on all surfaces with these hairs, but the red pigmentation occurs only on the petiole and petiolule (the leaflet stalk), and along principal veins on the lower leaflet surface. The upper leaflet is hairy but green. As the leaflet matures, the upper surface loses most of its hairiness and becomes somewhat rough, while the lower remains soft but eventually turns green. The red-orange "fur" persists on the petioles and stems, however, even long after the stems have grown thick and woody. Eventually, chocolate-brown bark forms on the main stems, which are very flexible.
One more surprise awaits you, if you have a hand lens. On the raised veins of the lower leaf, you will readily observe several dozen tiny white structures scattered across each leaflet. These appear to be butterfly eggs or minute insects--at least that's what I thought at first glance! But with a microscope the real identity cannot be mistaken. These many-celled structures are parts of the plant, and are rich in lipid (oil) droplets. The literature calls them pearl bodies or pearl glands. After carefully studying them on leaves of the unrelated balsa tree (Ochroma pyramidale), where they also occur along lower veins, Dennis O'Dowd (1980) suggested that pearl bodies probably function as ant food--that is, as a reward, presumably for the protection ants provide against herbivores (American Journal of Botany 67:543-549). Each pearl body has a constricted base and can be easily removed from the vein. We assume that pearl bodies are harvested quickly in nature, as the leaves expand, but at MEMBG, where leaf-tending ants are absent, some mature leaflets still possess these structures.
Larger, more spherical pearl bodies occur on the terminal branches of male and female inflorescences (flower clusters), on individual flower pedicels (stalks), and, occasionally, near the ovary base on female flowers. Like their counterparts on the leaves, these oily food bodies would provide a reward for ants while keeping them from robbing nectar and pollen from the flowers.
At MEMBG, Tetrastigma begins to flower in June, with the inflorescence originating from the axillary bud of the leaf. Each ultimate branch may have as many as fifty flowers arranged in a spheroidal cluster, and a large inflorescence may bear more than a thousand flowers. The individual flower, however, is small and not very showy. It is greenish in color, with four peculiar sepals, and has either four stamens (male flower) or a pistil with four stigma lobes (female flower). Nonetheless, when viewed through a hand lens, the simple flower is cute.
Arthur C. Gibson
Garden Director