ICKERT-BOND, STEFANIE, M.1* and RAYMOND, J. CRANFILL2. 1Department of Plant Biology, Box 871601, Arizona State University, Tempe, AZ 85287-1601; 2University and Jepson Herbaria, 1001 Valley Life Sciences Bldg. # 2465, University of California, Berkeley, CA 94720-2465. - Revisiting Stapf: Phylogeny of Ephedra, insights from plastid genes and morphology.
Phylogenetic analyses of seed plant evolution have demonstrated the
importance of the Gnetales. While these distinctive gymnosperms were
initially considered a sister group to the angiosperms, all recent
molecular analyses have refuted the anthophyte hypothesis, with some
even suggesting a close affinity to the pines. However, a sister
relationship of Gnetales to the Pinaceae is not easily reconciled with
morphology. This problem is further compounded by our incomplete
understanding of extant diversity in Ephedra, the basalmost
member of the Gnetales. To test Stapf's (1889) longstanding hypothesis
of relationships within Ephedra (Alatae, Asarca,
Pseudobaccatae) both morphological and nucleotide sequence data
sets were analyzed. These included data from the chloroplast
intergenic spacer regions (atpB-rbcL,
trnF-trnL) and the plastid coding region and spacer of
the rps4 gene. Our preliminary cladistic analysis suggests that
New World ephedras are paraphyletic, monophyly of this group requires
32 extra steps. While the analysis provides robust support for
monophyly of the Alatae clade, the monophyly of the
Asarca and Pseudobaccatae clades are not supported. The
traditionally accepted Old and New World clades are artificial. The
distribution of fleshy bracts, once considered taxonomically
important, requires two separate origins and a loss in the North
American "nevadensis-viridis alliance". Hence
it appears a relatively poor indicator of affinity. The topology also
supports a New World origin of Ephedra, with a single migration
event to the Old World. This scenario appears congruent with the
currently known fossil evidence, and may be further supported with
additional sampling. The apparent contrast between the low rate of
molecular divergence and remarkably rapid rates of morphological
differentiation may be tied to adaptive radiation of Ephedra in
extreme arid environments.
Key words: atpB-rbcL, Ephedra, morphology, phylogeny, rps4, systematics