1. Aristolochia L. (birthwort)
(Pfeifer, 1966)
Plants perennial
herbs or lianas (shrubs elsewhere). Aerial stems well developed, sometimes
twining. Leaves often appearing 2-ranked. Flowers zygomorphic, the calyx tube
well developed, hooked or S-shaped, with an expanded ring of tissue at the
juncture with the lobes. Stamens 6, the filaments fused with the style into a
column, the anthers without a sterile extension between the pollen sacs. Ovary
with 3 locules. Stigmas appearing as a low, irregular, 3-lobed crown at the tip
of the stylar column. Fruits dehiscing longitudinally into 3 or 6 valves. About
300 species, nearly worldwide but most diverse in tropical and subtropical
regions.
The sap of Aristolochia
species is yellowish and tastes bitter. Various species have been investigated
for the possible production of antitumor alkaloids and other compounds. These
same compounds, including aristolochic acid and trimethylamine, have also been
implicated as having carcinogenic properties. Bruised plant parts emit a faint,
unpleasant odor similar to that of turpentine, whereas the flowers of some
species sometimes emit an aroma similar to the scent of rotten meat.
Pollination in most species is a complex affair involving small flies that
become trapped overnight in the expanded basal chamber of the calyx tubes until
stiff, downwardly pointing hairs in the narrower portion of the calyx tube
relax, releasing the insect, which has been coated with pollen and departs to
pollinate a second flower in similar fashion. The leaves of Missouri species
are a principal larval food source for the eastern pipevine swallowtail butterfly
(Battus philenor philenor (L.)).