A Reappraisal of the Significance of Pollen in Classifications of the Gentianaceae

A reappraisal of the significance of pollen in classifications of the Gentianaceae

Siwert Nilsson , Magnus Hellbom, Wieslaw Smolenski

Grana 41: 90-106 (2002)

Abstract:

The tribal and subtribal classification of Gentianaceae published by Gilg (1895), which is mainly based on pollen morphological data, is compared with a recently published system (Struwe et al. 2002). The new classification is based on the phylogenetic analyses of molecular data and other characters, including palynology. The two classifications differ slightly in their circumscriptions of tribes and subtribes, and subsequently in the position of specific genera. The position and transfer of some genera from different groups in the older system (Gilg 1895) to other tribes/subtribes in the new system (Struwe et al. 2002) are discussed and evaluated on the basis of significant pollen data. It is considered that parallel evolution of exine patterns have occurred rather commonly in the Gentianaceae and, for example, tetrads seem to have evolved independently at least twice. The main exine patterns of gentian pollen are: striate, striato-reticulate, rugulate, reticulate, foveolate, perforate, with processes, or scabrate to smooth. The different patterns often intergrade to form a continuum, e.g., from striate to reticulate via striato- reticulate. The establishment of a new tribe, Saccifolieae has palynological support. The recent transfer of Ixanthus to the Chironieae, Macrocarpaea, Chorisepalum and Tachia (Zonanthus differs palynologically from Macrocarpaea, etc.) to the Helieae, Bartonia and Obolaria to the Gentianeae has palynological support. The removal of the genera Coutoubea, Schultesia, Symphyllophyton, Xestaea (Deianira possibly excepted) from the Helieae is also supported palynologically. The tribe Potalieae is a palynologically heterogenous group. The inclusion of Fagraea in the Potalieae seems natural, whereas pollen of Anthocleista and Potalia are reminiscent of that of some Loganiaceae.