POLLINATION OF RAFFLESIA (RAFFLESIACEAE)

<jats:p>The genus <jats:italic>Rqfflesia</jats:italic> includes about 13 species of parasitic flowering plants, among which are the largest known flowers. The flower with subtending scales is the only part of the plant external to the host and is produced solitary on roots (rarely stems) of the genus <jats:italic>Tetrastigma</jats:italic> (Vitaceae). Field studies were made of the pollination process in <jats:italic>R. pricei</jats:italic>, a species endemic to the Crocker Range in the Malaysian state of Sabah (northern Borneo). Pollination is mediated by carrion (bluebottle) flies of the genera <jats:italic>Lucilla</jats:italic> and <jats:italic>Chrysomya.</jats:italic> Experimental data indicate that both visual and olfactory cues are important in attracting flies to flowers. Flies (mostly female <jats:italic>L. papuensis</jats:italic>) obtain loads of the viscous liquid pollen matrix by visiting male flowers and entering anther grooves on the central column of the flower, precisely guided by ridges armed with hairs that force the fly into a position in which the pollen is positioned on the dorsal part of the thorax. “Windows” on the inside of the perigone diaphragm apparently help orient their flight inside flowers. Pollen‐loaded flies visiting female flowers may enter the infradiscoidal sulcus formed by a broad ring of stigmatic tissue above and the expanded base of the column below. On entering the sulcus the fly is wedged in so tightly that pollen is rubbed off the thorax onto the stigma. Only large flies could be effective in picking up pollen from male flowers and transferring it to female flowers. The pollination syndrome is sapromyophily, in which the flower closely parallels trap flowers of several other plant families, although it is not a trap. The flower provides no reward for pollinators but deceives them by an apparent offering of food and possibly brood place. <jats:italic>Rafflesia</jats:italic> plants are extremely rare, perhaps in part because of infrequency of pollination, which requires neighboring male and female flowers simultaneously in bloom.</jats:p>