Biosystematics and molecular phylogenetics of Brodiaea (Themidaceae) and related lilioid monocots

The resurrected plant family Themidaceae Salisb. contains 12 genera and 61 species of perennial geophytes principally from western North America. These genera, formerly recognized as tribe Brodiaeae in the Alliaceae, have also been previously divided into two complexes: the Milla complex centered in Mexico and the Brodiaea complex centered in the western United States. The Mexican genera are incompletely known, with several new species and a new genus recently being described. However, Brodiaea s.l. (e.g., Brodiaea, Dichelostemma, Triteleia) has been a classic example of evolutionary radiation in floral diversity, habitat specialization, and chromosome number.;This study provides the first robust phylogenetic analyses to describe the relationships among all twelve recognized genera of the Themidaceae. Data from DNA sequences of internal transcribed spacers regions of nuclear ribosomal RNA (ITS), twenty-six morphological characters, and plastid DNA sequences of ndhF, trnL-F, and rpl16 are presented. Within Themidaceae, four major clades are consistently identified in all of the individual and combined molecular analyses. The Milla complex of Mexico forms a clade within a paraphyletic Brodiaea complex of western North America. The species of Brodiaea and four of the five species of Dichelostemma form the core of a second clade, and collectively these two genera are sister to Dichelostemma capitatum and a monotypic Triteleiopsis. The third clade includes two monophyletic genera, Triteleia and Bloomeria, together forming a sister group to Muilla clevelandii. The other three species of Muilla are a monophyletic group sister to a monophyletic Androstephium in the fourth clade. These well-defined clades strongly suggest that the morphological characters (e.g., an extended perianth tube) that have been traditionally used to circumscribe the genera within Brodiaea complex have evolved independently at least twice. In addition, common biogeographic distribution patterns (e.g., Brodiaea and Triteleia having centers of diversity in northern California and the Pacific Northwest) appear to be the result of separate evolutionary radiations. Changes in nomenclature are recommended for Dichelostemma capitatum and Muilla clevelandii which have historically been a source of taxonomic confusion.