TRISTYLY IN THE ENDANGERED MASCARENE ISLAND ENDEMIC HUGONIA-SERRATA (LINACEAE)

Tristyly is a rare floral polymorphism known to occur in only five flo wering plant families. One unresolved and potential additional case of tristyly concerns the genus Hugonia in the Linaceae. Here we confirm the existence of tristyly in the genus by reporting floral measurement s made on Hugonia serrata Lam., an extremely rare species endemic to t he Mascarene Islands of La Reunion and Mauritius in the southern India n Ocean. We conducted an extensive search of all natural habitats on L a Reunion Island where the species had been previously reported. Twent y-eight individuals were found, of which nine were in flower. Of the n ine flowering individuals five had long-styled flowers with the stigma s placed above the two levels of anthers, three had intermediate lengt h styles with the stigmas placed between the two anther levels, and on e had stigmas placed below the two anther levels, i.e., three floral m orphs could be identified based on the sequence of stigma and anther p ositions. Reciprocity and precision indices calculated for sexual orga n length in each morph confirm that this variation is well within the range of values observed by previous workers on other tristylous speci es in other families. Our empirical data confirm the existence of tris tyly in the genus Hugonia, thereby raising the number of known familie s in which tristyly occurs to six. Pollen size, pollen number, and ant her length increased slightly with stamen length, but the low number o f plants precludes statistical tests of these trends. A bibliographic survey suggests that tristyly may occur in several other species of th e genus.