Molecular phylogeny of Scorzoneroides (Asteraceae): evolution of heterocarpy and annual habit in unpredictable environments.

It has been hypothesized that annual life history and heterocarpy are an adaptation to unpredictable habitats. In this paper, we infer a phylogenetic history for Scorzoneroides from the analysis of internal transcribed spacer (ITS) and plastid ndhF-rpl32 and rpl32-trnL sequences, on which we trace the evolution of one ecological (predictable vs unpredictable habitats) and two morphological (annual vs perennial and dimorphic vs homomorphic achenes) characters. Our results confirm the monophyly of Scorzoneroides and reveal the existence of two significant evolutionary lineages that do not coincide with major taxonomic subdivisions traditionally proposed for this genus. The first major group comprises taxa with all types of possible combinations of character states. The second major group includes exclusively homocarpic perennial taxa occurring in predictable habitats. It is strongly inferred that the most recent common ancestor of Scorzoneroides was perennial and homomorphic, and occurred in predictable habitats. The evolution of both annual life history and dimorphic achenes was significantly associated with occurrence in unpredictable habitats, which may suggest an adaptation process.