On the balance of evidence presented in these
pages, two competing hypotheses remain:
- either winged bean (Psophocarpus
tetragonolobus (L.) DC.)
began as an African species, perhaps Psophocarpus
grandiflorus Wilczek., and
was carried to Southern Asia where it under went domestication;
- or alternatively,
the wild progenitor of winged bean, perhaps resembling Psophocarpus
grandiflorus, has become extinct or has
yet to be located within Asia.
In favour of the first hypothesis, is the accumulating
evidence from taxonomy, cytology, and plant pathology, of close
similarities between African Psophocarpus
species and the winged bean. Many
other crops currently grown in Asia are known to have originated
in Africa. The long bean, a vegetable form of cowpea Vigna
unguiculata (L.) Walp., is
believed to have reached Asia through Ethiopia in prehistoric
times. Similarly, the bambara groundnut, Voandzeia
subterranean (L.) Thoars is
known to have been taken by Arab traders to Madagascar at an
early date. The progenitor of winged bean could have reached
Asia in a similar way.
Against the African hypothesis,
and in support of the Asian hypothesis, is the failure of attempts
to hybridise winged bean with P. scandens(Endl.)
Verdc., the modern day fragility of P.
its absence from lowland coastal sites, and the lack of any
clear evidence for its modern-day cultivation or spread by human
hands. In contrast to this, the genetic and cultural diversity
of winged bean referred to in these pages, points to a long
and rich encounter between plant and Man in Asia, especially
in its archipelago, that encompasses both lowland and highland
environments and a diversity of domestication trajectories.
the literature, there are many examples of discontinuities in
plant taxa across the Indian Ocean. The trans-oceanic distribution
may well turn out to be the result of ancient
geological events, rather than of dispersal by human hands.
However, there can be little doubt that the modern-day distribution
of winged bean is predominantly an artifact of human hands,
hands that have molded the plant to their own purposes, and
in so doing, extinguished, perhaps completely, its natural origins.
Further field exploration in Africa and Asia,
interspecific hybridisation studies, and the application of
molecular labeling techniques to representative collections
of the genus, will in time provide a test of these ideas. But
will it answer the question?
From where did winged bean arise?