International Aroid Society
  Amorphophallus Introduction and Taxonomic Description

by Wilbert Hetterscheid

The information here in is adapted from W. Hetterscheid and S. Ittenbach, 1996, "Everything You Always Wanted to Know About Amorphophallus, but Were Afraid to Stick Your Nose Into!!!!!", Aroideana 19: 7-131.

The plant genus Amorphophallus (Hetterscheid, 1994) belongs to the family Araceae (aroid family) and is estimated to encompass some 170 species. These are spread mainly in the tropics from West Africa eastward into Polynesia. None are found in the neotropics. They mostly grow in secondary forests or disturbed spots in primary forests and forest margins. Most are typical lowland plants.

Amorphophallus species are herbs with an underground storage organ. This is usually a tuber. One single leaf emerges from the tuber, consisting of a vertical petiole (stalk) and a horizontal leaf-blade. The latter is dissected into few or numerous small leaflets. Once plants are mature an inflorescence may develop. The inflorescence may replace the leaf in one season, or develop alongside it. As is typical for all other Araceae, the inflorescence consists of a foliar organ, the spathe, which usually envelops a stalk-like organ, the spadix. The actual flowers are tiny and strongly reduced and are found at the base of the spadix. The female flowers form the most basal zone and are each reduced to a mere pistil. Typical pollinator attracting organs (like a corolla) are absent. Above this zone is found a zone of highly reduced male flowers. They only exist of a group of stamens. The remainder of the spadix usually is sterile, lacking flowers, and is called the appendix. This entire structure, the spadix and the spathe, seems to work as one large "flower" and obviously acts as a unitary structure to attract pollinators, a feature lost by the actual individual flowers (Hay and Mabberley, 1991). After successful pollination most parts of the spathe wither and drop off, after which the individual female flowers develop into berries, containing the seeds. These berries are usually red or orange-red, but occasionally blue, white, or yellow-and- white. The berries are eaten by birds, although only few reliable observations exist (Hetterscheid, 1995).

Also few observations exist on (potential) Amorphophallus pollination (e.g. v.d. Pijl, 1937; Sivadasan and Sabu, 1991, Singh and Gadgil, 1996). In fact they mostly pertain to observing insects inside the spathe and whether they are actually effectively pollinating the flowers is not known (except by Sivadasan and Sabu, 1991). The spathe, having a cup-like base, may seem to be an insect-trap, although only part of the species seem to have their base so structured as to be an effective trap. Some of these have a strong constriction above the base, preventing insects from climbing out. A few others possess zones with hair-like organs, seemingly blocking the way out. The trapping of the pollinators is necessary for effective pollination from one flowering plant to another.

When the spathe opens the female flowers are receptive and must be pollinated that same day. The opening inflorescence emits an attractant scent. In Amorphophallus this scent has diversified considerably. In most species the scent is anything but pleasant, and reminds one of varieties of death, decay, sewage, gas and the like. A few species develop a scent that is actually pleasant to the human nose (e.g. carrot-like, anise, chocolate, fruity, lemon). The wide array of scents is presently analyzed chemically (Kite & Hetterscheid, 1997). Along with the fabric of these scents, parts of the spadix heat up considerably, notably the male zone and the appendix (Skubatch et al., 1990). Whether this helps volatilizing the chemicals that make up the scent, or works as an infrared attractant itself, or maybe both, is unknown. The illusion of death is supported in many species by dark brownish and brownish-purple colours, imitating decaying animals. Some species even posses hairs on the appendix, creating the illusion of a dead hairy mammal.

Once the insects have entered the spathe, they proceed downwards (or just drop) to the female zone where they can deposit pollen on the female flowers that they carried in from visiting another inflorescence. On this first day of flowering, the female flowers are receptive, whereas the male flowers are still closed and will not open until the next day, when the female flowers are no longer receptive. The insects therefore have to stay overnight to carry pollen away from the inflorescence. There seem to be several solutions presented to keep the insects in place. Important seems to be to provide for food. For this, Amorphophallus species either possess fleshy warts at the base of the spathe, or special organs are developed on the spadix. The latter are strongly modified male flowers (so called staminodes), that have lost the capacity to produce pollen but are transformed into protein-rich food bodies (Sivadasan & Sabu, 1991). Also, the appendix may serve as a food storage (Singh & Gadgil, 1996).

The next day, the male flowers open and a veritable rain of sticky pollen descends on the insects, still "trapped" in the base, after which they are released and may enter yet another inflorescence to pollinate.

Literature Cited

Hay, A. and D.J. Mabberley. 1991. 'Transference of function' and the origin of aroids: their significance in early angiosperm evolution. Bot. Jahrb. Syst. 113: 339-428.

Hetterscheid, W.L.A.. 1994. Preliminary taxonomy and morphology of Amorphophallus Blume ex Decaisne (Araceae). In: M.M. Serebreyanyi (ed.), Proc. Moscow Aroid Conference 1992: 35-48. Moscow.

Kite, G.C. and W.L.A. Hetterscheid. 1997. Inflorescence odours of Amorphophallus and Pseudodracontium (Araceae). Phytochemistry 46(1): 71-75.

Pijl, L. v.d. 1937. Biological and physiological observations on the inflorescence of Amorphophallus. Receuil Trav. Bot. Neerl. 34: 157-167.

Singh, S.N. and M. Gadgil. 1996. Ecology of Amorphophallus species in Uttara Kannada District of the Karnataka State, India: implications for conservation. Aroideana 18[1995]: 5-20.

Sivadasan, M. and T. Sabu. 1991. Beetle pollination - Cantharophily - in Amorphophallus hohenackeri (Araceae). Aroideana 12 (1-4)[1989]: 32-37.

Skubatch, H., T.A. Nelson, A.M. Dong, B.D.J. Meeuwse and A.J. Bendich. 1990. Infrared thermography of arum lily inflorescences. Planta 182: 432-436.