A banyan, also spelled "banian" (ˈbænjən ), is a fig that develops accessory trunks from adventitious prop roots, allowing the tree to spread outwards indefinitely. This distinguishes banyans from other trees with a strangler habit that begin life as an epiphyte, i.e. a plant that grows on another plant, when its seed germinates in a crack or crevice of a host tree or edifice. "Banyan" often specifically denotes Ficus benghalensis (the "Indian banyan"), which is the national tree of India, though the name has also been generalized to denominate all figs that share a common life cycle and used systematically in taxonomy to denominate the subgenus Urostigma. Like other fig species, banyans bear their fruit in the form of a structure called a "syconium". The syconium of Ficus species supply shelter and food for fig wasps and the trees depend on the fig wasps for pollination. Frugivore birds disperse the seeds of banyans. The seeds are small, and because most banyans grow in woodlands, a seedling that germinates on the ground is unlikely to survive. However, many seeds fall on the branches and stems of other trees or on human edifices, and when they germinate they grow roots down toward the ground and consequently may envelop part of the host tree or edifice. This is colloquially known as a "strangler" habit, which banyans share with a number of other tropical Ficus species, as well as some other unrelated genera such as Clusia and Metrosideros. The leaves of the banyan tree are large, leathery, glossy, green, and elliptical. Like most figs, the leaf bud is covered by two large scales. As the leaf develops the scales abscise. Young leaves have an attractive reddish tinge. Older banyan trees are characterized by aerial prop roots that mature into thick, woody trunks, which can become indistinguishable from the primary trunk with age. These aerial roots can become very numerous. the Kolcatta (Calcutta) Banyan, which has been tracked carefully for many years, currently has 2,880 supplementary trunks.