ABSTRACT.Following recent phylogenetic studies of the families and genera of Dioscoreales, the identification of monophyletic infrageneric taxa in the pantropical genus Dioscorea is a priority. A phylogenetic analysis based on sequence data from the plastid genes rbcL and matK is presented, using 67 species of Dioscorea and covering all the main Old World and selected New World lineages. The analysis used 14 outgroup taxa, including Trichopus Gaertn., Tacca J.R. & G. Forster, Stenomeris Planch., Burmannia L. and Thismia Griff. The main findings are: a) that a clade of rhizomatous taxa is sister to the rest of Dioscorea; b) the main Old World groups (such as the right-twining D. sect. Enantiophyllum) are monophyletic and c) there are two distinct lineages among the endemic Malagasy taxa. The consequences of the results for infrageneric classification of Dioscorea is considered, in particular the possibility of greatly simplifying the classifications of Knuth and Burkill. The results are also used to present novel hypotheses of character evolution in selected underground storage organ, inflorescence, fruit and seed characters and to discuss the origins of diversity in Dioscorea.

is a region of high plant diversity with an estimated 50,000 flowering plant species. Estimates of plant diversity in the region continue to grow as large numbers of new species are described even though there have been suggestions that there are few new species to be Gard. Bull. Singapore 71 (2) 2019 268 found in some parts of Southeast Asia. It is likely that most estimates of species numbers in the countries of Southeast Asia are too low due to the lack of taxonomic work on groups which have many locally endemic species. Differing collecting densities across the region can profoundly affect our understanding of plant diversity and lead to large underestimates of species diversity in poorly collected countries and regions. Progress on each of the major Flora

Khaosokia caricoides , D.A. Simpson, Chayam. & J. Parn., a newly discovered genus and species of Cyperaceae is described and illustrated. The genus is characterized by a narrowly paniculate dioecious inflorescence with 2-4 nodes, each of the nodes having a leaf-like inflorescence bract that exceeds the inflorescence. Spikelets in both sexes are linear-cylindric and each flower has seven perianth bristles. The nutlet was immature in the specimens examined. The photosynthetic pathway is C 3 . Khaosokia is endemic to limestone cliffs in peninsular Thailand; its conservation status is assessed as Vulnerable (VU B1a + 2a). It has affinities to tribes Cariceae, Dulichieae and some members of Scirpeae, but the exact nature of these relationships has yet to be determined. A revised key to the genera of Cyperaceae in Thailand is presented.

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Camptothecin (CPT) is an essential precursor of semisynthetic chemotherapeutic agents for cancers throughout the world. In spite of the rapid growth of market demand, CPT raw material is still harvested by extraction from Camptotheca acuminata and Nothapodytes foetida because its total synthesis is not cost-effective. In this study, we examined eight species of the genus Ophiorrhiza (Rubiaceae) from Thailand as novel alternative sources of CPT. CPT and/or 9-methoxy camptothecin (9-MCPT) were detected at different amounts in the leaf and root extracts of five species. We found that the CPT production ability of Ophiorrhiza spp. in Thailand was related mainly to species, not habitat. Chloroplast MATK and nuclear TOPI genes of eight species were investigated and compared with those of other Ophiorrhiza sequences from GenBank in order to classify and study the evolution in this genus. The molecular phylogenetic trees of both separated and combined MATK and TOPI nucleotide sequences revealed a major clade of Ophiorrhiza taxa correlated with production of CPT and its derivatives. Several amino acid markers of CPT- or 9-MCPT-producing Ophiorrhiza plants were also suggested from the alignment of TopI amino acid sequences. Our findings suggest that genetic factors play an important role in determining the CPT- and 9-MCPT-producing properties of Ophiorrhiza plants. Consequently, MATK and TOPI gene sequences could be utilized for the prediction of CPT and 9-MCPT production ability of members of Ophiorrhiza.