HUANG, MINGJUAN*, JOHN V. FREUDENSTEIN, and DANIEL J. CRAWFORD. Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, 1735 Neil Avenue, Columbus, OH 43210. - Systematics of Trichostema L. (Lamiaceae): evidence from ITS, ndhF, and morphology.
Trichostema L., a North American genus comprising five sections
and 17 species, has long been recognized as a natural group based on
its morphology. Since relationships among the species remain unclear,
cladistic analyses of morphological and molecular data for
Trichostema are needed to verify its monophyletic status and to
assess the sectional classification within the genus. Both ITS and
ndhF data indicate that Trichostema is monophyletic and
sister to the Asian Caryopteris s.s. When it includes T.
brachiatum, an eastern US species sometimes placed in its own
genus, section Orthopodium is polyphyletic, the remainder of
the species occurring in the western US. The ndhF data support
sections Paniculatum and Rhodanthum as sister to one
another. Vegetative structures, floral development, and fruit
morphology have been examined in much detail in combination with
characters available from the literature (pollen morphology, base
chromosome, and breeding system, etc.). In particular, the
characteristic trichomes (glandular and nonglandular) of
Trichostema have been studied and assessed for their
phylogenetic informativeness. The results of the morphological study
support the monophyly of Trichostema, and are mainly congruent
with relationships inferred from DNA sequence data, with the notable
exception of T. brachiatum, which is placed in section
Orthopodium.
Key words: ITS, Lamiaceae, morphology, ndhF, systematics, Trichostema