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Evolution of Caulanthus amplexicaulis var. barbarae (Brassicaceae), a rare serpentine endemic plant: a molecular phylogenetic perspective
Author(s) -
Pepper Alan E.,
Norwood Laura E.
Publication year - 2001
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.2307/3558456
Subject(s) - biology , monophyly , internal transcribed spacer , taxon , phylogenetic tree , botany , endemism , sister group , brassicaceae , subgenus , phylogenetics , molecular phylogenetics , evolutionary biology , clade , genus , zoology , ecology , genetics , gene
Intra‐ and interspecific phylogenetic relationships of the rare serpentine endemic taxon Caulanthus amplexicaulus var. barbarae and related taxa in the “Streptanthoid Complex” of genera ( Streptanthus, Caulanthus, Guillenia ) were examined using nuclear ribosomal internal transcribed spacer (ITS) and chloroplast trnL intron sequences. Phylogenetic hypotheses generated from 81 variable ITS nucleotide sites and six variable trnL nucleotide sites indicate that Streptanthus and Caulanthus are nonmonophyletic groups. Caulanthus amplexicaulis var. barbarae and its more widespread nonserpentine sister taxon Caulanthus amplexicaulis var. amplexicaulis formed a distinct monophyletic group. Among the taxa in our study, C. amplexicaulis was most closely related to Streptanthus tortuosus. The ITS sequences supported monophyly of subgenus Euclesia , which includes the bulk of the serpentine endemics in the Streptanthoid Complex. The serpentine taxa were nonmonophyletic, occurring in at least three distinct clades, suggesting that tolerance to serpentine may be gained or lost through relatively few genetic changes. Intraspecific ITS1 and ITS2 sequence divergence within C. amplexicaulis (1.3–1.8%) was higher than in comparable species (0.0–0.3%); implications of this genetic differentiation for the conservation status of C. amplexicaulis var. barbarae are discussed. Evidence is presented that supports a “biotype depletion” model for the origin of this rare endemic taxon.