title: Origin and diversification of the Milla Clade (Brodiaeoideae, Asparagaceae): a Neotropical group of six geophytic genera.
abstract: The Milla clade currently comprises six genera of geophytic plants distributed from Arizona to Guatemala. Three genera (Behria, Jaimehintonia and Petronymphe) are monotypic while the remaining genera (Bessera, Dandya and Milla) contain from two to ten (Milla) species. Parsimony, Maximum Likelihood and Bayesian Inference analyses were conducted with plastid and nuclear DNA sequences from a total of 181 plants belonging to 15 species in all six genera. Molecular dating was performed under a relaxed clock model. We examined the phylogenetic relationships of the genera and species, estimated origin-divergence times for the clade and genera and determined the ancestral distribution area of the clade by optimizing ancestral areas given current biogeographic distributions. The phylogenetic results suggest that final decisions on limits of the six genera in the Milla clade will have to be established until further taxonomic work is completed for Milla, in particular for the group of populations included under the name M. biflora. The later genus is rendered polyphyletic by other genera of the family. The origin of the Milla clade is estimated at 15.8Ma. Ancestral area of the clade most likely was located in the California Floristic Province and dispersal occurred most likely to the Chihuahuan-Coahuila Plateaus and the Trans-Mexican Volcanic Belt and from there to Baja California and the Sierra Madre del Sur. Two hypotheses that need further testing are proposed to explain complex relationships of genera and polyphyly of Milla, one in relation to fragmentation of populations and pollinator shifts and another suggesting that populations remained in refugia in the Trans-Mexican Volcanic Belt.
authors.affiliation: Biología Evolutiva, Instituto de Ecología, Carretera antigua a Coatepec 351, El Haya, 91070 Xalapa, Veracruz, Mexico.
authors.forename: Etelvina
authors.initials: E
authors.lastname: Gándara
authors.affiliation: Plant and Microbial Biology & The University and Jepson Herbaria, University of California, Berkeley, 431 Koshland Hall, Berkeley, CA 94270, USA.
authors.forename: Chelsea D
authors.initials: CD
authors.lastname: Specht
authors.affiliation: Biología Evolutiva, Instituto de Ecología, Carretera antigua a Coatepec 351, El Haya, 91070 Xalapa, Veracruz, Mexico. Electronic address: victoria.sosa@inecol.mx.
authors.forename: Victoria
authors.initials: V
authors.lastname: Sosa
mesh_terms: D001130:Arizona; D001499:Bayes Theorem; D005075:Biological Evolution; D002140:California; D018742:DNA, Chloroplast / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D016013:Likelihood Functions; D019668:Liliaceae / Q000145:classification* / Q000235:genetics; D008800:Mexico; D008957:Models, Genetic; D010802:Phylogeny; D017422:Sequence Analysis, DNA
chemical_list: D018742:DNA, Chloroplast; D018744:DNA, Plant
keywords: Ancestral area reconstruction; California Floristic Province; Chihuahuan Desert; Trans-Mexican Volcanic Belt