PLANA, VANESSA. Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, U.K.. - Morphological and molecular systematics of the Afro-Madagascan fleshy-fruited Begonia.
The phylogenetic relationships of African Begonia, in
particular those of the fleshy-fruited species, were assessed by
cladistic analysis of DNA sequences from the non-coding chloroplast
region trnL. In addition, a morphological cladistic analysis of
the fleshy-fruited species in sections Baccabegonia,
Squamibegonia, Tetraphila and Mezierea was
carried out to investigate relationships and character evolution. The
trnL phylogeny is generally congruent with that produced from
cladistic analyses of the internal transcribed spacer sequence data in
a previous study, although significant incongruences between both
topologies occur in the basal nodes. trnL and ITS data largely
agree with existing sectional concepts based on morphology and there
is overwhelming evidence from both data sets that the diversity of
Begonia is geographically structured. However, sequence data
has given strong evidence for some previously unsuspected
relationships. Fleshy-fruits arose at least twice in Africa, refuting
previous hypotheses which have suggested that fleshy-fruits represent
a single evolutionary event. The position of the endemic terrestrial
section from São Tomé, Baccabegonia, nested within an almost
exclusively epiphytic clade suggests its derivation from an epiphytic
ancestor. A new section to include B. iucunda is recommended,
in light of its isolated position in the both the trnL and ITS
phylogenies. This is supported by evidence from previous morphological
studies. Similarly B. loranthoides, currently included in
section Tetraphila, but distinct from other species in the
section, particularly in fruit morphology, could possibly merit a
section of its own. Morphology alone in Begonia is considered
unreliable for phylogenetic reconstruction, with most characters
showing high levels of homoplasy. Although most clades in the
molecular trees are supported by one or more morphological characters,
a small number of cryptic clades remain for which no obvious
morphological characters provide synapomorphies.
Key words: Africa, Begonia, phylogeny, trnL