Uniform TitleEvolution and systematics of the angiosperm order Gentianales with an in-depth focus on Loganiaceae and its species-rich and toxic genus Strychnos
NameFrasier, Cynthia L. (author), Struwe, Lena (chair), White, James (internal member), Messing, Joachim (internal member), Motley, Timothy (outside member), Rutgers University, Graduate School - New Brunswick,
DescriptionThe Gentianales includes five families known for their horticultural value and medicinal effects: Apocynaceae (milkweeds and rosy periwinkle), Gelsemiaceae (Carolina jessamine), Gentianaceae (gentians), Loganiaceae (strychnine plants), and Rubiaceae (coffee and quinine). They are a monophyletic assemblage, but the relationships between the families have been uncertain. The Loganiaceae are a mostly pantropical group with a few members reaching into temperate North America and Australia. This family includes 15 genera that have been divided into four tribes, one of which, Strychneae, was paraphyletic in previous analyses based on chloroplast and morphological data. Strychnos is the largest genus in Loganiaceae with approximately 200 species distributed throughout the tropics. This genus is well-known for its alkaloid production, in particular that of strychnine. Although strychnine has been popularized for its potential nefarious uses, many Strychnos species have been lauded for their medicinal properties conferred by other compounds. Strychnos was divided into 12 sections based on morphology, but the monophyly of these was in doubt as the sections were morphologically, chemically, and anatomically heterogenous. Combined analyses of four chloroplast regions, matK, ndhF, rbcL, and trnL, placed Rubiaceae as the most basal family in the Loganiaceae. Loganiaceae and Gelsemiaceae were the two subsequently diverging clades, and Apocynaceae and Gentianaceae were sisters in the most nested position. Within the Loganiaceae, tribe Antonieae was basal to all other tribes. Strychneae was resolved as monophyletic only when morphology was included in a combined analysis with a nuclear ribosomal gene region (ITS) and rps16 of the chloroplast genome. An analysis of the secondary structure of the ITS region resulted in possible new synapomorphies for tribes Antonieae and Spigelieae within the Loganiaceae. The current sectional treatment of Strychnos does not reflect the evolution of the genus, and recommendations for improving the classification will be made. This work will have large implications for the understanding of chemical and morphological evolution on ordinal, familial, and tribal levels in the Gentianales, and provides a framework for further studies in biogeography, habit evolution, and speciation processes.
NoteIncludes bibliographical references.
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.