Geographic cohesion, chromosomal evolution, parallel adaptive radiations, and consequent floral adaptations in<i>Calochortus</i>(Calochortaceae): evidence from a cpDNA phylogeny

Abstract

• We developed a molecular phylogeny for Calochortus (Liliaceae) to reconstruct historical patterns of evolution. • Three cpDNA segments were sequenced and analyzed using parsimony. • We identified seven major, geographically cohesive clades centered mainly in the California Floristic Province. Section Calochortus is monophyletic; section Mariposa, paraphyletic; and section Cyclobothra, polyphyletic. Calochortus arose in the Coast Ranges, which were uplifited 3–5 million yr ago. Three of the four major floral syndromes evolved at least twice, associated with particular environments. Serpentine tolerance evolved at least seven times. • We argue that limited dispersal led to the narrow endemism of individual species, the geographic cohesion of clades, and parallel radiations in habitat preference, floral morphology, and serpentine tolerance. Chromosomal evolution allowed Calochortus to ‘double-up’ its regional radiations, preventing crosses between pairs of clades with overlapping ranges. Floral evolution in Calochortus is an example of consequent radiation, with selection for local diversification in habitat driving secondary specialization of flowers on the range of pollinators and abiotic conditions within each habitat, rather than selection to partition pollinators within habitats driving adaptive radiation.