Lactoris fernandeziana Phil., monotypic in its family, is endemic to the cloud forests of Robinson Crusoe Island. Although there has been considerable study of the relationships of Lactoris, as a rare species and as a putative primitive paleoherb, little is known of its reproductive biology. Knowledge of the latter is essential for effective conservation. The species is gynomonoecious and protogynous. The overall proportion of flowers is about 1 female: 1 hermaphrodite. The inconspicuous semi-pendulous green flowers, usually in mixed gender inflorescences, do not produce rewards. Hermaphrodite flowers are herkogamous and dichogamous. Pollen grains are shed from the extrorse anthers in permanent dry tetrads. The mean number of tetrads per hermaphrodite flower is 12 879. Both flower types bear an average of about 18 ovules. The P/O ratios imply facultative or obligate xenogamy, but, hand pollinations show that Lactoris is self-compatible. No floral visitors were ever observed, but stigmata of open pollinated flowers bore tetrads, and 64% of such styles had pollen tubes. Flowers enclosed in mesh (1 mm) bags bore similar numbers of tetrads and pollen tubes. Thus, we conclude that Lactoris is anemophilous. Low genetic diversity (isozymes and DNA) supports selfing and implies limited distance wind pollen dispersal. The small size of the island, the 1 000-2 000 extant Lactoris plants, coupled with anemophily, self-compatibility and pendant flower position, has yielded a geitonogamous system with high seed set, and low genetic diversity. If inbreeding depression is expressed, it is in seed germination and seedling vigor, for Lactoris is very difficult to cultivate. For this species, effective conservation practices need to focus on habitat preservation and promotion of outcrossing.

Key words: Basal angiosperms; conservation biology; island biology; monoecy; self-compatibility; wind pollination.