When encountering this slender twining plant with heart-shaped leaves in thickets, one might intuitively think of some weedy plants such as Mile-a-Minute (Mikania cordata, Compositae) or Morning Glories (Convolvulaceae). However, the subject of this article, Aristolochia acuminata (Aristolochiaceae). is less known and does not spread rampantly as do the above plants.
The Aristolochia (Dutchman’s pipe or Birthwort) from tropical America with large showy flowers produce some of the most sought after ornamentals that every decent garden grows over their pergola. Our native Aristolochia species, however, do not have showy flowers but they best exemplify the insect-plant relationship in terms of pollination and as host plants.
Aristolochia acuminata (better known by its ‘old name’ A. tagala) or Akar ketola hutan in Malay is characterised by its oval lamina with a deeply heart-shaped base, a perianth with a globular flask-shaped base (utricle) that narrows into a funnel-shaped limb with a tongue-like lobe. Its fruit is a papery capsule that splits from the stalk into 6 valves when mature and hangs like an inverted parachute. The winged seeds are dispersed by wind.
The protogynous flowers, which are structurally highly modified, are most probably adapted to fly pollination. Flies attracted by the rotten fruit smell enter and move further down the utricle attracted by the translucent window. There they get trapped within by stiff downward pointing hairs inside the tube wall. Secretory hair patches in the utricle provide food to keep the trapped insects alive until the anthers mature and shed pollen. The hairs then wither allowing the insect to leave covered in pollen and possibly to visit another flower with receptive stigmas so effecting cross-pollination.
The Birdwing butterflies (Papilionidae) are attracted to lay their eggs on aristolochiaceous plants due to their aristolochic acids sequestration habit (Nishida et al, 1993). The caterpillars feed exclusively on Aristolochiaceae plants. They sequestrate the poisonous aristolochic acids without being poisoned themselves. This habit plays an important role in chemical defence against predation, and hence maintaining the host fidelity (Weintraub, 1995). Researchers in the Penang Butterfly Farm grow Aristolochia acuminata as the food plant for Yellow Birdwing (Troides helena) conservation programme (http://www.butterfly-insect.com/yellow-birdwings/).
Besides its important ecological role as a food plant for Birdwing butterflies, Akar ketola hutan was used in traditional medicine. The leaves are pounded and applied to the head for fever (Burkill, 1966). Recent studies have confirmed that aristolochic acids or their derivatives found in Aristolochia species have several adverse effects on human health and of several animal species (Kiew, 1999). A ban on aristolochic acids in traditional herbal preparations has been enforced in several countries.
