FRITSCH, PETER W. Department of Botany, California Academy of Sciences, Golden Gate Park, San Francisco, CA 94118. - The historical biogeography of Antillean Styrax (Styracaceae).
A morphological phylogenetic analysis of Styrax (120 species)
has suggested that no two of the four Antillean species of this genus
form sister-group relationships: one groups in a clade of southern
North American endemics, and the rest are each distributed among
different clades of otherwise South American species. In particular,
S. obtusifolius (Cuba and Hispaņola) has been considered the
basal member in a clade of small-flowered, gynodioecious species
otherwise endemic to South America. Here these relationships are
tested with DNA sequence data from the ITS region. In contrast to the
morphological analysis, phylogenetic analysis of the ITS data set
recovers a strongly supported sister-group relationship between S.
obtusifolius and the Puerto Rican endemic S. portoricensis,
and this clade is nested within a group of fully bisexual South
American species. The other two gynodioecious species sampled form a
monophyletic group that is well removed from S. obtusifolius.
Incongruence length difference tests suggest that overall conflict
between the ITS and morphological data sets of neotropical evergreen
Styrax is mainly attributable to the conflict between the data
profiles in S. obtusifolius. All morphological characters
supporting a relationship between S. obtusifolius and the other
gynodioecious species are associated with gynodioecy and floral
reduction, suggesting that the similarity in breeding system and
floral characters among distantly related Cuban and South American
species of Styrax represents a remarkable case of convergent
evolution. This scenario is consistent with the prevalence of
small-flowered species in the Cuban flora that have apparently
coevolved with endemic and highly specialized microscopic insect
pollinators, and with the trend toward dicliny on islands. Although
Styrax is apparently boreotropical in origin, Antillean
Styrax species have originated through dispersal from South
America, as inferred from DIVA analysis. Styrax ochraceus,
endemic to Hispaņola, still requires assessment in this context.
Key words: biogeography, Caribbean, DIVA, gynodioecy, ITS region, Styrax