MALCOMBER, SIMON T.* AND ELIZABETH A. KELLOGG. Missouri Botanical Garden, PO Box 299, Saint Louis, MO 63166-0299 and Department of Biology, University of Missouri, Saint Louis, MO 63121. - Gaertnera (Rubiaceae): a rapid radiation based on sequence data from three nuclear DNA sequence data sets.
Gaertnera (Gaertnereae, Rubiaceae) is a well-defined genus of
approximately 70 species, with a paleotropical distribution
encompassing Western Africa, Madagascar, Mascarenes, Sri Lanka and
Southeast Asia. In addition to its wide geographical range, the genus
also exhibits a large degree of morphological diversity, and is one of
only twelve angiosperm genera in which dioecy has evolved from
distylous ancestors. Prior to testing predictions from two
alternative hypotheses for the evolution of dioecy in ancestrally
distylous taxa it is necessary to reconstruct a phylogenetic estimate
for the genus. Molecular phylogenetic estimates for Gaertnera
are presented based on sequence data from 30-40 species for three nDNA
markers; ITS (Internal Transcribed Spacer), Tpi (Triose
phosphate isomerase) and PepC (Phosphoenolpyruvate
carboxylase). Counter to our expectations based on the morphological
differences and geographical separation between the sampled species,
all markers reconstruct a rapid radiation for the genus. A combined
analysis of all three markers will be discussed, in addition to
molecular clock estimates for the divergence time of Gaertnera
from its South American sister taxon, Pagamea.
Key words: Gaertnera, ITS, low-copy markers, PepC, Rubiaceae, Tpi