FISHBEIN, MARK1*, ROBERTA J. MASON-GAMER1, DEBORAH J. HOPP1, ERIN DOUTHIT1, and STEVEN P. LYNCH2. 1Department of Biological Sciences, University of Idaho, P.O. Box 443051, Moscow, Idaho, 83844-3051, USA; 2Department of Biological Sciences, Louisiana State University, One University Place, Shreveport, Louisiana, 71115-2399, USA. - Phylogeny of North American Asclepias estimated from non-coding chloroplast (rpl16 intron and trnC-rpoB spacer) DNA sequences.
Asclepias is a large genus with about 120 species native to
North America. The genus has been of great interest to systematists,
ecologists, and evolutionary biologists because of complex floral
morphology, specialized interactions with insect herbivores, and low
fruit set suggestive of sexual selection. Current understanding of
phylogenetic relationships within Asclepias is based on the
last comprehensive monograph of the genus and cladistic analysis of
morphological data. To further explore these relationships, DNA
sequences from two non-coding regions of the chloroplast genome were
analyzed. Sequences were obtained from the rpl16 intron (c.
1200 bp) and the trnC-rpoB spacer (c. 1175 bp) regions for
samples representing 100 species. Analyses of these sequences resulted
in phylogenetic trees in which several small clades were strongly
supported, but for which relationships among these clades and
remaining species were supported quite weakly. The strongly supported
clades correspond to several of the smaller infrageneric groupings
(e.g., subg. Podostemma, ser. Incarnatae) identified in the
most recent generic revision. Well supported relationships conflicting
with that revision suggest that earlier classification relied too
strongly on a small set of floral characters (e.g., shape of corona
segments), to the exclusion of vegetative characters (e.g., growth
form). Our results are consistent with a rapid radiation of
Asclepias in North America.
Key words: Asclepias, chloroplast, phylogeny, rapid radiation, rpl16, trnC-rpoB