The present geographical distribution of Amorphophallus largely comprises the paleotropics. Western Africa is the westernmost limit whereas the easternmost limit lies in Polynesia. However, this eastern boundary is formed by the occurrence of A. paeoniifolius, a species that has a long history of cultivation in Asia, and there is considerable doubt whether its present distribution mirrors its natural distribution. Disregarding A. paeoniifolius, the eastern limit of Amorphophallus is the line Japan-Philippines-Taiwan-New Guinea-N.E. Australia, formed respectively by A. kiusianus (Makino) Makino (Japan, Taiwan), several species of the Philippines and A. galbra F.M. Bailey (New Guinea, Australia). Within the west and east boundary, Amorphophallus is found throughout the tropical and some subtropical zones.
Within this generic distribution Amorphophallus species show a very high degree of endemism. Only three species show a fair geographical range. A. paeoniifolius is found from Madagascar eastward into Polynesia (but see above), A. muelleri is found from Central Thailand, southward via Sumatra, Java to the Lesser Sunda Islands and A. abyssinicus has a fairly large distribution in Africa. All other species show much more local distributions. Part of this may be the effect of sampling bias but recent active collecting largely confirms the restricted geographical range of the vast majority of species. Some of the species distribution patterns form a dense mosaic and suggest that the genus is at least in some areas actively speciating. This is supported by the fact that closely related species are very often found in neighboring areas. This pattern seems to result in seven large areas of endemism in the genus's distribution. These are
3. Southern and central India.
4. Northern India-Myanmar(Burma)-northern Thailand-southern and southeastern China-Laos-North Vietnam.
5. Central Thailand-Cambodia-South and central Vietnam-eastern China (mainland)-Taiwan-Japan.
6. Malaysia-Sumatra-Java-Borneo-Lesser Sunda Islands-New Guinea-northern Australia.
Borneo is an area of overlap in this scheme.
The majority of Amorphophallus species seem to be pioneers in disturbed vegetations. Many are found at forest margins, in open savannah forests, on (steep) slopes, in disturbed parts of primary forest, and sometimes in very exposed parts in limestone karst areas. Relatively few species are known to live in dense forest. Roughly there is a division possible in the genus between species found in strongly seasonal climates (e.g. most of Africa, India, Thailand, Indochina, Java), and those found in more wet climates (e.g. Sumatra, Borneo). Species may be found in soils on granitic bedrock, but more often in limestone areas. The altitudinal range varies from sea level to circa 3000 meters (the latter especially in the northernmost limits of the genus). Flowering starts mostly just prior to the onset of the rains. In Asia flowering specimens that are effectively pollinated will not develop leaves anymore that season (except for three "evergreen" species), but the African species will always develop leaves in each growing season, whether flowering or not.
Pollination observations are scarce for Amorphophallus species. Earlier this century, v.d. Pijl (1937) gathered some observations on the pollination of A. muelleri (syn. A. oncophyllus), A. titanum, and A. variabilis, from which it seems that carrion beetles and small staphylinid beetles are the pollinators. Sivadasan & Sabu (Aroideana 12[1-4], 1991 ) describe the nitidulid pollinators of A. hohenackeri in detail and their behavior. Recent observations (Hetterscheid, 1995) of a flowering A. titanum in the wild, suggest action by sweat bees (Trigona alliance) but doubt has been cast on the usefulness of that observation, as it now seems that sweat bees are not particularly discriminating in their visiting behavior (pers. comm. G. Hambali, Indonesia). The first author however also caught quite an array of carrion and dung beetles in a flowering A. gigas on Sumatra. A publication on the pollinators of Amorphophallus is forthcoming (Huijbrechts & Hetterscheid, in prep.).
Equally little is known about the distributors of Amorphophallus seed, although no one doubts that birds are the main group. This follows from the quite strongly and brightly coloured berries. The gigantic berries of A. titanum are almost certainly eaten and dispersed by Hornbill birds (Hetterscheid, 1995), whereas those of A. gigas are dispersed by Bulbuls (Hetterscheid, 1995). Bulbuls are also known to disperse Amorphophallus seeds in India (Singh & Gadgil, 1996) and Sabah (pers. comm. A. Lamb). Quite remarkable is the occurrence of blue berried species exclusively in the northernmost range of Amorphophallus, suggesting dispersal by a particular group of birds restricted to that particular geography.
Amorphophallus titanum is locally abundant on Sumatra and may be found in populations of several tens of individuals. On a larger scale, several hundreds of plants may be found in areas of several square kilometers. But the distribution is patchy and over large areas not one single specimen may be found. Only a few areas lining the Barisan range have been investigated for the presence of A. titanum. The populations always contain many more seedlings and immature specimens than mature ones. Reports are known of large amounts ("truck loads") of tubers of A. titanum being transported to Japan and Korea, collected by underpaid locals. Needless to say, the search is for the largest specimens, yielding the most material for the least effort. This means that mature specimens will soon be over corrected in populations, and when immature specimens are collected next, no plants will reach flowering size. So the population will soon diminish and disappear, the more so since A. titanum does not multiply vegetatively, despite incorrect reports in literature to the contrary.
Another threat may be the destruction of relatively "undisturbed" secondary forest. Amorphophallus titanum is mostly found in secondary forest with occasional old forest giants and young trees forming a loose canopy, as may be found in old colonial plantations. The enormous attention focused on the conservation of virginal primary forest may lead to an underestimation of the importance of secondary forest for biodiversity in general.
A third threat would be the disappearance of the species' pollinator and distributor. Sweat bees are probably not easy to expel from the forests, but the giant Hornbills may be much more vulnerable in the face of trophy hunting and habitat destruction. In the face of this, A. titanum certainly qualifies for adding to the CITES convention lists (Hetterscheid & v. Vliet, 1996).
The question may arise whether botanical gardens can contribute to the conservation of such a species as A. titanum. A positive role of botanical gardens in the conservation of plant species in general can only be reached when their infrastructure allows for the establishment of an artificial population of a species, covering as large a portion as possible of it's genomic diversity. If not, the value of such a collection is limited in terms of conservation. In the case of A. titanum, genomic diversity seems quite limited. Throughout its range the species is astoundingly homogeneous in morphology, both in vegetative and generative parts. This may mirror a rather strongly constrained genome and could therefore lead to a successful conservation by establishing populations in botanical gardens. Artificial fertilization is easy and this may continue the diversity in such circumstances.
A second role for botanical gardens would be to show to the public the astounding aspects of the biology of this vegetable dinosaur and so create a positive general attitude towards the costly conservation of this species and of plants in general.
Hetterscheid, W.L.A. 1995. Sumatran Amorphophallus adventures: 20 August - 1 September 1993. Aroideana 17: 61-77.
Hetterscheid, W.L.A. and G.J.C.M. v. Vliet. 1996. Amorphophallus, giant from the forest. CITES/C&M 2(4): 86-96.
Pijl, L. van der. 1937. Biological and physiological observations on the inflorescence of Amorphophallus. Rec. 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: 5-20.
Sivadasan, M. and Sabu, T. 1991. Beetle pollination --cantharophily-- in Amorphophallus hohenackeri (Araceae). Aroideana 12[1-4],: 32-36.