The genus Exacum (Gentianaceae)

Sammanfattning: In this monograph the paleotropical genus Exacum (Gentianaceae) is revised. Sixtyfive species are recognized. Of these, 21 species occur in Ceylon, India and SE Asia, 4 in Socotra and Oman, 38 in Madagascar and 2 in continental Africa. Twenty-three new species are described, one of which, E. grande Klack., from India and the remaining, viz. E. amplexicaule Klack., E. anisopterum Klack., E. appendiculatum Klack., E. conglomeratum Klack., E. dipterum Klack., E. dol ichantherum Klack.E. exiguum Klack., E. giganteum Klack., E. gracile Klack., E. humbertii Klack., E. intermedium Klack., E. latifolium Klack.,E. naviculare Klack., E. nossibeense Klack., E. microcarpum Klack., E. penni- nerve Klack., E. rotundifolium Klack., E, speciosum Klack., E. stenophyllum Klack., E. stenopterum Klack., E. umbellatum Klack, and E. undulatum Klack., from Madagascar. New combinations and names are: E. 1 inearifoliuiiTTHumbert) Klack., E. oldenlandioides (S. Moore) Klack., and E. subteres Klack. Two sections are presented, viz. section Exacum comprising 21 species in Asia and section Africana Klack, comprising 44 species in Africa (including Madagascar and Socotra). Various aspects of the morphology are discussed including micromorphology of seeds and pollen grains as seen by means of SEM. A key as well as typification, maps and drawings of all species are given. A hypothesis of the cladistic relationship of the species of Exacum is presented and discussed with reference to related genera. Phytogeography and vicariance patterns within the genus in general, and the Asiatic taxa in particular, are discussed.