Monophyly and relationships of the tribe Exaceae (Gentianaceae) inferred from nuclear ribosomal and chloroplast DNA sequences

Abstract

Both chloroplast trnL (UAA) intron and nuclear ribosomal ITS sequences highly confirmed the monophyly of the tribes of the Gentianaceae defined by the recent classification, and revealed the tribe Exaceae as a basal clade just next to the basal-most lineage, the tribe Saccifolieae. Within the tribe Exaceae, Sebaea (except Sebaea madagascariensis) appeared as the most basal clade as the sister group to the rest of the tribe. The Madagascan endemic genera Gentianothamnus and Tachiadenus were very closely related to each other, together standing as sister to a clade comprising Sebaea madagascariensis, Ornichia, and Exacum. The saprophytic genus Cotylanthera nested deeply inside Exacum. Sebaea madagascariensis was shown closer to the Madagascan endemic genus Ornichia than to any other sampled Sebaea species. Exacum appeared as the most derived taxon within this tribe. The topology of the phylogenetic trees conform with the Gondwana vicariance hypothesis regarding the biogeography of Exaceae. However, no evidence for matching the older relationships within the family to the tectonic history could be corroborated with various divergence time analyses. Divergence dating estimated a post-Gondwana diverging of the Gentianaceae about 50 million years ago (MYA), and the tribe Exaceae as about 40 MYA. The Mozambique Channel land-bridge could have played an important role in the biogeographic history of the tribe Exaceae.

ANDEAN SPECIATION AND VICARIANCE IN NEOTROPICAL MACROCARPAEA (GENTIANACEAE–HELIEAE)1

“…Given the position of the tribe in the family phylogeny and an estimated age of 42-50 Ma for the whole Gentianaceae (Yuan et al, 2003), we can assume that the Helieae, and maybe the genus Macrocarpaea as well, has been in South America for at least 30 million years. Macrocarpaea is part of one of the more basal divergences in the tribe (the Macrocarpaea subclade), with only the southeast Brazilian genera Prepusa Mart.…”

Langaside, a novel secoiridolactone glycoside derivative from Tachiadenus longiflorus Griseb. (Gentianaceae) formed by a [2+2] cycloaddition reaction

“…The fruit is a one-celled capsule filled with numerous minute seeds (Klackenberg, 1990). In Madagascar, T. longiflorus is currently used by the Bezanozano, Sihanaka and Merina tribes as a purgative and to treat fever and fatigue , Yuan et al, 2003. The stem of T. longiflorus has been investigated previously and yielded scoparone, scopoletin (Del Rio et al, 2004, Heitz et al, 1979, oleanolic acid (Heitz et al, 1979), oleanolic acid methyl ester , diosmin, diosmetin (Del Rio et al, 2004, Heitz et al, 1979, and the iridoid, angelone .…”

Exacum Tenue (blume) Klack. (Gentianaceae):A New Record for the Flora of Eastern Himalaya

“…Formerly, these species were recognized in the distinct genus Cotylanthera Blume (Lace 1914;Smith et al 1921;Hara 1975). Based on recent molecular studies (Yuan et al 2003(Yuan et al , 2005 and morphological analysis, all the species of the genus Cotylanthera were assigned to genus Exacum L. (Klackenberg 2006). In India, the achlorophyllous mycoheterotrophic herbs of this genus is represented by three species (E. paucisquamum, E. nanum and E. tenue), of which two (E. paucisquamum and E. nanum) were reported earlier from the Eastern Himalaya (Clarke 1883;Averyanov et al 2014).…”

“…On careful examination of the specimens using taxonomic literature (Averyanov et al 2014;Biswal et al 2011;Klackenberg 2006;Tiwari et al 2015;Yuan et al 2003), online e-flora illustrations (Flora of China) and expert scrutiny, the species was identified as Exacum tenue (Blume) Klack. Standard taxonomic methods were used for collection, processing, and preparation of the herbarium specimens (Jain & Rao 1977;Bridson & Forman 1998).…”