Amorphophallus (from Ancient Greek amorphos, "without form, misshapen" + phallos, "penis") is a large genus of some 170 tropical and subtropical tuberous herbaceous plants from the Arum family (Araceae).
These are typical lowland plants, growing in the tropical and subtropical zones of the paleotropics, from West Africa to the Pacific Islands. None of them are found in the Americas although a remarkably similar but not closely related genus, Dracontium, has evolved there. Most species are endemic. They grow preferably on disturbed grounds, such as secondary forests.
These small to massive plants grow from a subterranean tuber, Amorphophallus tubers vary greatly from species to species, from the quite uniformally globose tuber of A. konjac to the elongated tubers of A. longituberosus and macrorhizus to the bizarre clustered rootstock of A. coaetaneus. From the top of this tuber a single leaf, which can be several metres across in larger species, is produced atop a trunk like petiole followed, on maturity, by a single inflorescence. This leaf consists of a vertical leaf stalk and a horizontal blade, which may consist of a number of small leaflets. The leaf lasts one growing season. The peduncle (the primary flower stalk) can be long or short.
As is typical of the Arum family, these species develop an inflorescence consisting of an elongate or ovate spathe (a sheathing bract) which usually envelops the spadix (a flower spike with a fleshy axis). The spathe can have different colors, but mostly brownish-purple of whitish-green. On the inside, they contain ridges or warts, functioning as insect traps.
The plants are monoecious. The spadix has tiny flowers : female flowers, no more than a pistil, at the bottom, then male flowers, actually a group of stamens, and then a blank sterile area. This last part, called 'the appendix', consists of sterile flowers, called 'staminodes', and can be especially large. There is no corolla.
Once the spathe opens, pollination must happen the same day. The inflorescence, in many species, emits a scent of decaying flesh, in order to attract insects, though a number of species give off a pleasant odor. Through a number of ingenious insect traps, pollinating insects are kept inside the spathe to deposit pollen on the female flowers, these stay receptive for only one day, while the male flowers are still closed. These open the next day, but by then female flowers are no longer receptive and so self pollination is avoided. The male flowers shower the trapped insects with pollen. Once the insects escape, they can then pollinate another flower. Amorphophallus species are used as food plants by the larvae of some Lepidoptera (butterfly and moth) species including Palpifer sexnotatus and Palpifer sordida.
The titan arum, the world's biggest inflorescence, belongs to this genus. It can reach a height of 2.5 m and a width of 1.5 m. A runner-up is Amorphophallus gigas, which is taller, but has a somewhat smaller flower. Amorphophallus konjac tubers are used to make , a Japanese thickening agent and edible jelly containing glucomannan.
Some species are called voodoo lily, as are some species of Typhonium (also in the Araceae).
The name 'Amorphophallus' is derived from the Greek words 'amorphos' and 'phallos', meaning 'shapeless penis', in reference to the prominent spadix appendix.
Site with descriptions and images of Amorphophallus: http://www.cate-araceae.org/taxon/Index.do?id=10767