Authors: Weber, A.; Burtt, B. L.
Publication: Beitrage zur Biologie der Pflanzen
Year: 1998
Genera: Codonoboea, Didymocarpus, Gyrocheilos, Henckelia, Hovanella, Loxocarpus, Platyadenia

A survey of Didynocarpus Wall. (Gesneriaceae-Cyrtandroideae) in its current, unwarrantably wide usage is made and results in its division into three, apparently not very closely related genera: (1) Didymocarpus Wall. s. str. (including Gyrocheilos W. T. Wang), (2) Henckelia Spreng. (1817: previously nomen rejiciendum in favour of Didymocarpus) and (3) Hovanella A. Weber & B. L. Burtt (previously Didymocarpus sect. Hova C. B. Clarke). Didymocarpus is now an essentially Sino-Himalayan genus of about 80 species, extending southwards through Myanmar (Burma), Vietnam and Thailand to the Malay Peninsula where there are about eight species (one, D. cordatus, being also recorded here from Sumatra); its salient features are its fruits (‘orthocarpic’, dehiscing loculicidally along both sutures, usually narrowed at base and often distinctly stipitate) and habit (perennials with annual or monocarpic flowering stems). Henkelia, of which the type is a S. Indian plant, becomes a large genus that includes not only all the species of S. India and Sri Lanka (Didymocarpus sect. Orthoboea Beth.), but also the bulk of the Malesian species hitherto referred to Didymocarpus, as well as the genera Loxocarpus R. Br., Codonoboea Ridl., and Platyadenia B. L. Burtt.; its salient features lie in the fruits (‘plagiocarpic’: making an angle with the pedicel and held more or less horizontally, dehiscent only along the dorsal suture, not narrowed at base) and its habit (perennial, often woody stems or rosettes with continuous growth). Hovanella, with two species in Madagascar, somewhat resembles Henckelia in the plagiocarpic-follicular fruits, but has distinctive seed-coat-characters (as seen under SEM) that confirm its alliance with other African genera. The new classification is shown to be supported by the available cytological data and is consistent with the general pattern of the phytogeography of Old World Gesneriaceae. Some evolutionary trends in this group are briefly discussed. The better-established sections of ‘Malesian Didymocarpus‘ are transferred to Henckelia (other names available for future transfer if required are listed) and one new section Glossadenia A. Weber & B. L. Burtt is diagnosed.

The necessary new specific combinations into Henckelia and Hovanella are incorporated in a list of names (alphabetical by specific epithet), which includes all those placed under Didymocarpus for Malesia, with their correct assignments.

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