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Dischidia major or Malayan Urn Vine is an unusual plant first encountered in 1772 as a specimen sent from Madras to Nathaniel Wallich, the curator of the Calcutta Botanical Garden. He published a description in the second volume of Plantae Asiaticae rariores and named it Dischidia rafflesiana in honour of his late friend Sir Stamford Raffles, the founder of Singapore. The honorific did not survive the test of time, but the peculiar morphology of the plant persists. 'Dischidia' is derived from the Greek, meaning "cleft in two" and refers to the apically bifid staminal corona.
Dischidia is a genus of some 80 species of trailing, twining or scandent, succulent epiphytes found throughout the tropics of Asia (New Guinea, Moluccas, Philippines, India, tropical Australia, Hong Kong, Taiwan) through to the western Pacific. They carry modified leaves offering accommodation to ants, including those of the family Dolichoderinae, and in return gain some sustenance from increased carbon dioxide and nitrogen levels, and a degree of protection from noxious animals and plants. This mutualism trait, known as myrmecophily, is widespread across the plant world and clearly carries considerable benefits for both ants and plant.
Dischidia major twines around the branches and trunks of trees, having a preference for those that are decaying. It produces both circular succulent leaves of about 2 cm diameter, and hollow, pouch-like 12 cm long leaves, reminiscent of the fruits of Araujia sericifera, a related species. These modified leaves, pitchers or ascidia, are purplish and richly dotted with stomata on the inner surface, and have an opening at the top end near the stalk. Organic debris and rainwater, possibly augmented by secreted fluids, accumulate in the cavity over the course of time, offering a source of nutrition which the plant utilises by growing roots into the chamber. Dischidia astephana and D. parvifolia do not provide housing for resident ants, but have roots that penetrate decaying wood and humus, reaching into the ant nests and presumably obtaining nutrients from the ant waste there.
Assimilating insect remains places Dischidia in the same category as Sarracenia, Nepenthes, Cephalotus and other plants using a fluid reservoir to digest organic debris. The line between well-adapted and poorly adapted carnivory is a blurred one, so that assigning a plant to the carnivorous category may be difficult. (see Protocarnivorous plant)
Dischidia major flowers are yellow striped with green, and arranged in few or many-flowered umbels. The fruit of D. major consists of the usual horn-shaped pair of follicles while the seed has a tuft of silky hairs at one end and includes an edible portion or elaiosome as incentive for ants to move the seed (myrmecochory) into nests inside the tree with an improved chance of germination and growth.
- The Ecology and Evolution of Ant-Plant Interactions - Victor Rico-Gray & Paulo S. Oliveira (University of Chicago Press, 2007)