Reproductive biology of Lactoris fernandeziana (Lactoridaceae)

Lactoris fernandeziana, monotypic in its family, is endemic to the cloud fo rests of Robinson Crusoe Island. Although there has been considerable study of the relationships of Lactoris, as a rare species and as a putative prim itive paleoherb, little is known of its reproductive biology. Knowledge of the latter is essential for effective conservation programs. The species is gynomonoecious. The overall proportion of flowers is similar to 1 female:1 hermaphrodite. The inconspicuous semipendulous green flowers, usually in m ixed-gender inflorescences, do not produce rewards. Hermaphrodite flowers a re herkogamous and protogynous. Pollen grains are shed from the extrorse an thers in permanent dry tetrads. There is a mean of 12879 tetrads per hermap hrodite flower. Both flower types bear an average of similar to 18 ovules. The P/O (pollen/ovule) ratios imply facultative or obligate xenogamy, but h and pollinations show that Lactoris is self-compatible. No floral visitors were ever observed, but stigmata of open pollinated flowers bore tetrads, a nd 64% of such styles had pollen tubes. Flowers enclosed in large mesh (1 m m) bags bore similar numbers of tetrads and pollen tubes. Thus, we conclude that Lactoris is anemophilous, a syndrome perhaps reflected by the P/O rat io. Low generic diversity (isozymes and DNA) supports selfing and implies l imited distance wind pollen dispersal. The small size of the island, the +/ - 1000 extant Lactoris plants, coupled with anemophily, self-compatibility, and pendant flower position, have 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 difficu lt to cultivate. For this species, effective conservation practices need to focus on habitat preservation and promotion of outcrossing.