Molecular species delimitation, taxonomy and biogeography of Sri Lankan Gesneriaceae
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Date
30/11/2017Item status
Restricted AccessEmbargo end date
30/11/2018Author
Ranasinghe, Subhani Wathsala
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Abstract
The plant family Gesneriaceae is represented in Sri Lanka by six genera:
Aeschynanthus, Epithema, Championia, Henckelia, Rhynchoglossum and
Rhynchotechum, with 13 species (plus one subspecies/variety) of which ten are
endemic including the monotypic genus Championia, according to the last revision
in 1981. They are exclusively distributed in undisturbed habitats, and some have high
ornamental value. The species are morphologically diverse, but face a problem of
taxonomic delineation, which is further complicated by the presence of putative
hybrids.
Sri Lanka and Indian Peninsula, represent the Deccan plate of the ancient
Gondwanan supercontinent. The presence of a relict flora may indicate the
significance of the geological history of the Deccan plate for the evolution of
angiosperms. The high degree of endemism here, along with their affinities to the
global angiosperm flora paints a complex picture, but its biogeographic history is still
unclear. The pantropical family Gesneriaceae distributed in Sri Lanka and South
India is therefore an appropriate study group in this context. Besides, the family itself
has a complex but largely unresolved biogeographical history especially concerning
the origin and diversification of Old World Gesneriaceae.
Modern approaches for the taxonomic studies were applied, integrating
morphological and molecular data. Multiple samples were collected for each species
across their geographical distribution. Nuclear ITS and chloroplast trnL-F sequences
for the taxa from Sri Lanka were used to generate regional genus phylogenies of all
six genera, using maximum parsimony. The rate of evolution of the nuclear ITS
region versus chloroplast trnL-F was varied greatly across the six genera studied.
Molecular delimitations were mostly congruent with the classical taxonomy.
Over 65 taxonomic characters were studied in detail to recognize synapomorphies for
clades and taxa. A complete taxonomic revision of Gesneriaceae in Sri Lanka,
including lectotypification, was conducted based on both, the molecular and
morphological data. This resulted in the recognition of 14 species in the six genera,
including one newly described species H. wijesundarae Ranasinghe and
Mich.Möller. Henckelia communis and H. angusta were not supported molecularly
as two separate entities but are recognized as two species because of consistent
morphological differences between them. Henckelia humboldtiana is proposed to
represent a species complex due to its highly variable and inconsistent molecular and
morphological diversity and overlap with H. incana and H. floccosa; more research
is needed here. National conservation assessments were conducted, and all 14 species
were recognized as threatened.
Biogeographic affinities of Sri Lankan Gesneriaceae were elucidated, generating a
dated phylogeny using an existing matrix of four plastid gene regions; trnL-F, matK,
rps16 and ndhF, amended by sequences generated in this study. The final combined
matrix included 175 taxa including newly generated sequences for the 13 Sri Lankan
taxa. Phylogenetic trees were generated using parsimony, maximum likelihood and
Bayesian inference. Molecular dating was carried out using BEAST and ancestral
area reconstruction using BioGeoBears. These analyses indicated that the six genera
of Gesneriaceae arrived in Sri Lanka separately and sometimes different time
periods. One lineage dated back to the early diversification of the subfamily
Didymocarpoideae (generally regarded as the Old World Gesneriaceae), which
occurred around the KT boundary, before the Deccan plate was connected to Asia.