STRUWE, LENA* AND VICTOR A. ALBERT. Cullman Program, The New York Botanical Garden, Bronx, NY 10458, Botanical Institute, Copenhagen University, Gothersgade 140, DK-1123 Copenhagen K, DENMARK. - Supermerous corollas, fleshy fruits, and pantropical biogeography in Anthocleista, Fagraea, and Potalia (Gentianaceae).
The woody and fleshy-fruited genera Anthocleista,
Fagraea, and Potalia (Gentianaceae) are tree- or
shrub-like tropical gentians previously associated with Loganiaceae.
Molecular data from rbcL, matK, and the trnL
intron (along with morphological and phytochemical evidence) has shown
that this group is deeply nested inside Gentianaceae. Specific
relationships of the group are to lineages of herbaceous and
dry-fruited genera that are more basally placed, implying secondary
derivations of tree-like habit and fleshy fruits in the family.
Anthocleista and Potalia also diverge from the usual
gentian floral bauplan in having supermerous corollas and staminal
parts (being 8-16-merous). SEM studies have revealed multiplication
of corolline and staminal primordia based on an initially 4-merous
primordia area. Anthocleista, Fagraea, and
Potalia also appear to lack postgenital fusion of carpels,
which is typical for other gentians. The congenitally fused carpels
in these genera may have predisposed evolution of their fleshy,
indehiscent fruits. Preliminary results from nuclear ITS (internal
transcribed spacer) sequences show the three genera to be
monophyletic, with African-Malagasy Anthocleista sister to
American Potalia, and with Asian-Australian-Pacific
Fagraea as the sister to this pair. This is in contradiction
to an earlier morphology-based cladistic study, which showed a
paraphyletic Fagraea. Morphology-based species level results
in Potalia show white-sand, narrowly endemic species from
central Amazonia to be most basally placed, and species from Central
America, Guianas, and non-white-sand Amazonian areas in more derived
positions. This supports the hypothesis that lowland white-sand areas
in the Neotropics may be relictual areas that harbor many ancestral
and phylogenetically divergent plant lineages.
Key words: biogeography, floral development, Gentianaceae, molecular systematics, phylogeny, Potalieae