Of the nine named species of Psophocarpus
DC., it is only winged bean, P.
tetragonolobus (L.) DC., that is found
extensively outside of Africa.
Detailed taxonomic studies suggest that the nearest African species
to winged bean are the naturally occurring species P.
scandens (Endl.) Verdc.
and P. grandiflorus
Wilczek. Though morphologically distinct from winged bean, both species
share with it the chromosome number 2n=18 as well as the same preference
for moist equatorial habitats.
a predominantly lowland distribution
(0 to 1000 m above sea level) and is widespread
in central and east Africa, including Madagascar.
grandiflorus, on the other hand,
is a rare species, with a range restricted to humid pockets in the mountains
of central and north central Africa (Teza, Virunga, Ruwenzori, Elgon
and Southern Ethiopia) at an altitude between 1600 and 2300 m above
Attempts to hybridise species of Psophocarpus DC.
Given the similarities in chromosome number and type
between winged bean and P.
it is notable that all attempts to
hybridise the two species have failed. Nor, up
until now, has winged bean been hybridised with P.
grandiflorus, because when the two
species have been grown alongside one another, it has not been possible
to synchronise flowering to the level required for cross-pollination.
contrast to these attempts at interspecific crosses, intraspecific crosses
between winged bean varieties from widely separated parts of Asia and
Melanesia, are nearly always successful.
hypothesised progenitor of winged bean
hypothesis that P.
the wild progenitor of winged bean, was first proposed in 1980.
The pods and seeds of three species
P. scandens, P.
grandiflorus, and P. tetragonolobus
(the winged bean), from left to right.
first sight, P.
resembles winged bean more closely than does P.
it has a climbing rather than creeping habit and a more open inflorescence
with larger flower parts, pods and seeds. However, while natural stands
are harvested for their edible leaves, pods and beans, nowhere in modern
Africa, is P.
recorded as being
planted, let alone cultivated. On the other hand, P.
is planted and cultivated for its vegetable parts and also as a cover
crop in some parts of its natural area of distribution.