Pollen morphology of tribe Trichosporeae (Gesneriaceae) in China and its systematic significance

Morphological studies of pollen of twelve species in four genera of tribe Trichosporeae (Gesneriaceae) from China are reported in this paper. The pollen grains of tribe Trichosporeae are tricolporoidate or rarely tricolporate, suboblate or spheroidal in shape, circular or subangular in polar view and nearly round or round in equatorial view. Pollen varies in size, colpus characters and ornamentation between species and genera. There is a fragmentary reticular tectum on the colpus membrane of Loxostigma griffithii, and this type of tectum probably represents a comparatively primitive character. In Aeschynanthus, the pollen grains of sections Haplotrichum and Diplotrichum, in which the corolla usually has indistinct bilabiate limbs, are comparatively small; in sections Microtrichum, Xanthanos and Aeschynanthus, in which the corolla has distinct bilabiate limbs, the pollen grains are large. The delimitation of the two ends of the colpi in section Didymocarpoides, which is terrestrial and primitive in the genus Lysionotus, is indistinct, although it is distinct in section Lysionotus. Based on this study, and on information in relevant references, a key to the genera of tribe Trichosporeae is presented based on characteristics of the pollen grains.