A taxonomic revision of the genus Henckelia Spreng. (Gesneriaceae) in Thailand and surrounding countries

Abstract

Henckelia was described in 1817 by Sprengel. The name Henkelia honours a German administrator and amateur botanist, L.V.F. Henckel von Donnersmarck (1785-1861). Currently Henckelia contains 68 species globally. This thesis focused on the taxonomic revision of Henckelia in Thailand and surrounding countries (Myanmar, Laos, Cambodia and Vietnam). A total of 24 species are recognized in Thailand. Identification keys and full descriptions (including illustrations) are provided for all 24 species including data on distribution and conservation status. Five new species are discovered and described i.e. Henckelia amplexifolia Sirim., H. campanuliflora Sirim., H. candida Sirim., H. dasycalyx Sirim. & D.J. Middleton and H. nakianensis Sirim., J. Parn. & Hodk. The morphological investigation was extended to a morphometric analysis. Morphological data were analysed using non-metric multidimensional scaling (NMDS), with Jaccard as the distance measure. The morphometric analysis divided the 24 species into two groups. Group one consists of taxa with single leaf, campanulate flower, reniform anthers and peltate or subpeltate stigma. Group two consists of taxa with several leaves, infundibuliform flowers, elliptic anthers and bilobed stigma. Henckelia amplexifolia is unique in having a stolon and bulbils and producing less fruit. A molecular phylogenetic study was carried out on Henckelia and related genera using newly sequenced species and existing data from GenBank. Four DNA sequence regions were used, namely the nuclear ribosomal ITS, and plastid trnL-F, atpB-rbcL and rps16 regions. The DNA datasets were used to reconstruct phylogenetic trees with Bayesian Inference and Maximum Parsimony analyses. A Henckelia clade containing groups A-F (see below) was well supported (1.00 PP). Thus, the genus Henckelia sensu Weber et al. (2011), and Middleton et al. (2013) is shown to be monophyletic. Heckelia was shown to be sister to a clade of other genera including Allocheilos, Gyrocheilos, Didymocarpus, Liebigia and Cathayanthe. The relationships of Henckelia species are well resolved and supported and six groups were defined (A to F). A group of Henckelia longisepala and H. urticifolia are the most outlying taxa of Henckelia sequenced here. The tree separated the Henckelia species well and it is clear that the DNA regions will be valuable for future DNA barcoding work on the group especially nrITS and trnL-F which are particularly well represented for Henckelia species. A study of the pollen morphology of Henckelia is presented for the first time using SEM. Light and SEM analysis showed that Henckelia pollen grains are tricolpate, and that the shape ranges from subprolate to euprolate. The pollen grains are small to medium size and the exine sculpturing is reticulate. Photographs were taken and a master key based on pollen morphology is provided.