Abstract

Crossostylis (Rhizophoraceae) is one of the inland genera of Rhizophoraceae. Its distribution is on the South Pacific Islands, encompassing New Caledonia, the Fiji Islands, Vanuatu, the Solomon Islands, Samoa, the Society Islands and the Marquesas Islands. Species of this genus show morphological diversity especially of the inflorescences, flowers and seed coats. Based on cladistic analyses of morphological characters and restriction site variation of chloroplast DNA (cpDNA), we discuss phylogeny, speciation and evolutionary trends of morphological characters in Crossostylis. Cladistic analyses based on morphological and DNA data yield the same topological cladogram. Phylogenetic analyses suggest that species of Crossostylis are divided into two pronounced monophyletic groups: one comprising six species distributed on the Solomon Islands, Vanuatu and the Fiji Islands, and the other comprising four species distributed on New Caledonia and Polynesia. Monophyly of the former group agrees with general assumptions of phytogeographical affinities, but the monophyletic Polynesia–New Caledonian species group is not coincident with general floristic affinities for the region. All species endemic to the Fiji Islands are very closely related and this suggests speciation from a single ancestor on the islands. Some morphological characters were optimized on the cpDNA tree obtained and examined for evolutionary trends. Many of the floral morphological features support macromolecular clades, but all seed coat characters are homoplasious. Perhaps this reflects high adaptive significance, such as is involved with seed dispersal.

Crossostylis J. R. Forst. et G. Forst, one of the inland genera of Rhizophoraceae, is distributed on the major islands of the South Pacific.