title: Pleistocene radiation of the serpentine-adapted genus Hesperolinon and other divergence times in Linaceae (Malpighiales).
abstract: OBJECTIVE
  Hesperolinon (western flax; Linaceae) is endemic to the western United States, where it is notable for its high and geographically concentrated species diversity on serpentine-derived soils and for its use as a model system in disease ecology. We used a phylogenetic framework to test a long-standing hypothesis that Hesperolinon is a neoendemic radiation.
  
  
  METHODS
  Five plastid and two ribosomal nuclear DNA gene regions were sampled from 105 populations of Hesperolinon, including all 13 recently recognized species across their known ranges. We used these data to generate population-level phylogenies of Hesperolinon. We also generated a robustly sampled chronogram of Linaceae using an eight-gene, 100-taxon supermatrix calibrated using fossil Linum pollen and a published chronogram of Malpighiales.
  
  
  RESULTS
  Most diversification in Hesperolinon has taken place in the past 1-2 million yr, much more recently than previous estimates. Only the earliest-diverging species, H. drymarioides, was resolved as a clade. Denser taxon and gene sampling generally support previously proposed relationships within Linaceae, but with more recent diversification of key clades.
  
  
  CONCLUSIONS
  Hesperolinon is an excellent example of edaphic neoendemism, in support of Raven and Axelrod's hypothesis for the genus. Dense population-level sampling reveals a complex of incipient species, with clades poorly aligned with traditional morphological circumscriptions, likely due in part to continued gene flow. The diversification of Linaceae is more recent than previously estimated, and other recent radiations (e.g., Hugonia) warrant further study.
authors: Department of Integrative Biology and Jepson Herbarium, 1001 Valley Life Sciences Building, University of California, Berkeley, California 94720, USA acschneider@berkeley.edu.
authors: Adam C
authors: AC
authors: Schneider
authors: Department of Integrative Biology and Jepson Herbarium, 1001 Valley Life Sciences Building, University of California, Berkeley, California 94720, USA.
authors: William A
authors: WA
authors: Freyman
authors: Department of Integrative Biology and Jepson Herbarium, 1001 Valley Life Sciences Building, University of California, Berkeley, California 94720, USA Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, California 93105, USA.
authors: C Matt
authors: CM
authors: Guilliams
authors: Venice Bike Fix, 1101 Ocean Front Walk, Venice, California 90291, USA.
authors: Yuri P
authors: YP
authors: Springer
authors: Department of Integrative Biology and Jepson Herbarium, 1001 Valley Life Sciences Building, University of California, Berkeley, California 94720, USA.
authors: Bruce G
authors: BG
authors: Baldwin
mesh_terms: D005075:Biological Evolution; D002140:California; D018742:DNA, Chloroplast / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D019143:Evolution, Molecular; D019658:Linaceae / Q000235:genetics* / Q000502:physiology; D008969:Molecular Sequence Data; D009922:Oregon; D010802:Phylogeny; D017422:Sequence Analysis, DNA
chemical_list: D018742:DNA, Chloroplast; D004275:DNA, Ribosomal
keywords: California Floristic Province; Hesperolinon; Linaceae; chronogram; neoendemic; serpentine; supermatrix