Phylogenetic and morphometric analysis of Plantago section Coronopus (Plantaginaceae)

Plantago sect. Coronopus contains our two focal species (P. coronopus L., P. crassifolia Forssk.), both with an overall conspicuous bi-hemispheric distribution range (Mediterranean and Middle Eastern regions in the Northern Hemisphere and South Africa in the Southern Hemisphere). We have evaluated up to 27 morphological characters from 96 herbarium specimens representing five out of seven species of that section that are currently recognised using principal coordinate analysis, linear discriminant analyses, agglomerative clustering, and classification tree analyses, in order to test the current taxonomic concepts of our two focal species. Furthermore, we used 54 individuals representing six out of those seven species of P. sect. Coronopus to construct molecular phylogenetic hypotheses by sequencing nuclear ribosomal DNA from the internal transcribed spacer region (ITS), the plastid trnL-F region, the plastid intergenic spacer region trnH-psbA and adopting maximum likelihood and Bayesian inference analyses. In the Northern Hemisphere, an Irano-Arabian clade initially identified as P. coronopus and shown as distinct in both morphological and phylogenetical terms fits a wider circumscription of P. crypsoides Boiss. due to lack of the prominent short and thick inflorescence scape following Boissier's description. The morphological differences between P. crassifolia from the Mediterranean region and P. crassifolia from South Africa (often named P. carnosa Lam.) were marginal, yet the molecular phylogenetic analyses of both nuclear and plastid markers clearly separated these evolutionary entities. Therefore, we re-instated the name P. carnosa as the correct name for South African P. crassifolia. Plantago carnosa differs from P. crassifolia by the combination of having stronger woody rootstocks, which are more often branched, by broader leaves (>= 1.6mm wide) and the fact that specimens more often turn brown when dried. Our dataset provides the best sampled phylogenetic hypothesis for P. sect. (and subg.) Coronopus to date, and reveals discordance between nuclear and plastid genealogies within P. sect. Maritima, which requires further investigation.