Systematics Section / ASPT
Powell, E. Ann , Kron, Kathleen A. .
Molecular systematics of Rhododendron subgenus Tsutsusi (Rhodoreae, Ericoideae, Ericaceae).
Rhododendron subgenus Tsutsusi, commonly known as evergreen azaleas, includes approximately 117 deciduous and evergreen species from Japan, China and northeastern Asia. Subgenus Tsutsusi has been divided into two sections, Brachycalyx and Tsutsusi, based o要 characteristics of the leaves, young twigs and corolla. However, this subgenus has not been assessed using a phylogenetic framework. We obtained molecular data from three chloroplast (matK, ndhF and trnS-trnG-trnG) and two nuclear (nrITS and the third intron of rpb2) regions for 22 species of Rhododendron (14 species from subgenus Tsutsusi), 3 species of Menziesia, and o要e outgroup (Therorhodion camtschaticum). Parsimony and likelihood analyses based o要 total evidence were used to assess the monophyly of subgenus Tsutsusi, determine its phylogenetic position in Rhodoreae, and assess the monophyly of sections Brachycalyx and Tsutsusi. Select morphological characters were scored from species descriptions and were mapped o要 the molecular tree using Maclade. Results show that subgenus Tsutsusi is monophyletic and that the presence of axillary vegetative buds o要 the growth of the previous year is a synapomorphy for the subgenus. Menziesia is monophyletic and is sister to subgenus Tsutsusi (with low support). A sister relationship between these clades has not been previously proposed and this novel finding would suggest that Menziesia is derived from within Rhododendron. Sections Brachycalyx and Tsutsusi are both monophyletic. Taxa in section Brachycalyx share a unique 17 base pair indel in trnS-trnG-trnG and have pseudoverticillate, rhombic and monomorphic leaves. In section Tsutsusi, leaves are dimorphic, not rhombic nor pseudoverticillate, and young twigs have flattened multicellular hairs. The Menziesia + subgenus Tsutsusi clade is sister to subgenus Rhododendron. Relationships among other subgenera in Rhododendron are not well-supported or resolved and require further investigation.
1 - Wake Forest University, Department of Biology, P.O. Box 7325, Winston-Salem, North Carolina, 27109-7325, U.S.A.
Presentation Type: Paper
Location: Cottonwood B (Snowbird Center)
Date: Tuesday, August 3rd, 2004
Time: 3:15 PM