Taxonomic revision and pollination biology of orchid genera Crepidium Blume and Dienia Lindl. (MALAXIDINAE, ORCHIDACEAE) in Thailand

Abstract

The terrestrial orchid Crepidium Blume and Dienia Lindl. in Thailand were enumerated by Gunnar Seidenfaden under Malaxis with key and drawings. Because of no species descriptions in publication, it is difficult to delimit species boundary. Moreover, recent discovery of new species results in unreliable assessment of species, therefore, the taxonomic revision of Crepidium and Dienia in Thailand should be carried out. The results indicated that the column and transversal callus on labellum are taxonomically important characters to delimit these two genera. In addition, morphological characters, i.e. stem and leaf morphology, labellum auricles, margins and number of teeth on distal margin of labellum, and high ridges on labellum cavity, are useful characters to classify and identify to species. It is suggested that only 1 species of Dienia and 25 species of Crepidium are distributed in Thailand. Four species are new records for Thailand, namely, C. bahanense (Hand.-Mazz.) S. C. Chen & J. J. Wood, C. josephianum (Rchb. f.) Marg., C. maximowiczianum (King & Pantl.) Szlach. and C. micranthum (Hook. f.) Szlach. and a new species, C. falcifolium Nuammee, Seelanan & H. A. Pedersen. Furthermore, the two new combinations are made and substantiated, i.e. C. chamaeorchis (Schltr.) Nuammee, Seelanan, Suddee & H. A. Pedersen and C. szemaoense (Tang & F. T. Wang) Nuammee, Seelanan, Suddee & H. A. Pedersen.

The investigation on pollination biology of C. acuminatum (D. Don) Szlach and D. ophrydis (J. Koenig) Ormerod & Seidenf. indicated that C. acuminatum is likely cross-pollinated orchid that relies on pollinators for successful pollination. In contrary, D. ophrydis is autonomous self-pollination assisted by rain whose pollination mechanism was assisted by viscous drops and water adhesion. Both C. acuminatum and D. ophrydis produced and secreted nectar to possibly attract pollinators. The much lower percentages of natural fruit set of C. acuminatum may be due to self-incompatibility, pollinator limitation, coupling with other environmental factors. Whilst, D. ophrydis may employ nectar as attractant to pollinators in order to increasing chance for outcrossing but autonomous self-pollination assisted by rain thus seem to be an important strategy that guarantees fruit set when pollinator’s visits are scarce.