HARDY, CHRISTOPHER R.* AND DENNIS WM. STEVENSON. L.H. Bailey Hortorium, Cornell University, Ithaca, NY 14853-4301 and New York Botanical Garden, Bronx, NY 10458-5126. - The unusual androecium and pollination system in Cochliostema (Commelinaceae).
Flowers of the neotropical genus Cochliostema are the largest
and among the most complex and fragrant in Commelinaceae.
Cochliostema is further characterized by its peculiar
androecium consisting of three fertile stamens and three antherless
staminodes. The fertile stamens are on one side of the flower and
united by their filaments, forming a compound structure that curves to
the flower's right as the flower opens. The anthers are longitudinally
dehiscent, spirally coiled, and enveloped by petaloid extensions of
the filaments of the two lateral stamens contributing to the
three-staminate structure. The coiled form of the mature anthers is
achieved through the prolonged and spiral growth of the apical
portions of the developing thecae. The coiling of the thecae in this
manner results in a significant increase in volume devoted to pollen
production in a relatively compact space. The two petaloid envelopes
(or "cuculli") emerge as papillate processes on either side
of the filaments of the two antepetalous stamens. Laminar growth of
the cuculli proceeds such that both contribute equally in the
formation of a common chamber surrounding all three anthers. Field and
laboratory studies indicate that pollen is expelled from the chamber
primarily through the apical terminus of a hose-like, slightly
supervolute, extension of each cucullus through vibration of the
entire staminal structure by certain pollen-collecting bees.
Euglossine and xylocopine bees found "buzzing" the flowers
of Cochliostema in the field were captured and observations
using an SEM revealed an abundance of Cochliostema pollen
deposited on the bees' hind legs. These data indicate that the cuculli
of Cochliostema are, in many respects, functionally analogous
to the poricidal thecae of many buzz-pollinated flowers, thereby
confirming the predictions made by previous authors. These data also
identify certain euglossine and xylocopine bees as probable vectors in
pollen transfer between flowers of Cochliostema.
Key words: androecium, buzz pollination, Cochliostema, Commelinaceae, floral development