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Taxonomy, phylogenetic relationships and pollination biology of Tacca (Dioscoriaceae)

Gwynne Lim (USA)

The award from IAPT was used to cover part of my travel expenses from New York to Hong Kong and Southeast Asia. During the trip, I have managed to accomplish three of my objectives: 1. Obtaining specimens of Bornean species. 2. Testing my hypothesis that showy Tacca species have thermogenic flowers and 3. Examining material in herbaria in Southeast Asia.

During this trip, I have collected specimens of Tacca from Hong Kong and Sarawak, including T. bibracteata Drenth, T. borneensis Ridl. (Figure), T. palmata Blume (Figure 1), T. leontopetaloides Kuntze, and T. integrifolia Ker Gawl. The first two species are bornean endemics, as is a specimen I collected that is tentatively labeled as T. reducta P.C. Boyce & S. Julia, as it was not in flower and cannot be conclusively identified.

I discovered more complexity in the reproductive biology of showy Tacca. I collected scent volatiles of Theobroma cacao and T. borneensis flowers in field. I observed and recorded thermogenesis from the flowers of Tacca chantrieri, Tacca borneensis (Figure 3) and Tacca integrifolia, but not for Tacca plantaginea. This is the first record of thermogenesis in the genus as well as in the family Dioscoreaceae and order Dioscoreales. This trip was vital in confirming my hypothesis that multiple showy members of Tacca are thermogenic, while non-showy members have consistently failed to demonstrate thermogenesis upon anthesis.

I trapped insect fauna on the flowers of T. borneensis. These may be likely pollinators, although there is good reason to believe many species of Tacca are predominantly selfing.

Finally, I made collections of living material, deposited at the Singapore Botanic Gardens (SING), DNA and herbarium vouchers. More living and herbarium specimens have been examined from collections in SING, a major repository of Southeast Asian material, where Tacca species diversity is highest. I am confident that most of the currently accepted species limits are justified, with a few exceptions. One of them is Tacca integrifolia, which is easily distinguished by its predominantly white, paired outer involucral bracts. Molecular and morphological evidence seems to imply that there are multiple species.

After work at the respective field sites during this trip, I visited SING, HK, and SAR herbaria to annotate and examine specimens for my taxonomic revision of the genus.


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