Phylogenetics and evolution of phyllotaxy in the Solomon's seal genusPolygonatum(Asparagaceae: Polygonateae)

Abstract

Polygonatum is the largest and most complex genus in tribe Polygonateae, comprising approximately 57 species widely distributed in the warm temperate, subtropical and boreal zones of the Northern Hemisphere. However, phylogenetic relationships in the genus remain poorly understood. The objectives of this study were to reconstruct the phylogenetic relationships of the genus using four plastid markers, and to examine the evolution of leaf arrangement in Polygonatum in the phylogenetic context of its closely related taxa. Thirty Polygonatum species were sampled to infer phylogenetic relationships using maximum-likelihood and Bayesian analyses. The evolution of leaf arrangements was reconstructed using Bayesian, parsimony and likelihood methods. The phylogenetic analyses supported the current generic delimitation of Polygonatum, with Heteropolygonatum recognized as a distinct genus. Three major lineages in Polygonatum were well supported, largely correlated with geographical distribution and the most recent classification at the sectional level. However, our results did not support the currently recognized series, especially the two large series Verticillata and Alternifolia.Bayesian analyses support the alternate-leaf arrangement as the ancestral state for Polygonatum, but parsimony and maximum-likelihood analyses suggest an equivocal state for crown Polygonatum. Leaf arrangement was found to be evolutionarily labile. A new nomenclatural combination was made: Polygonatum sectionSibirica (L.I.Abramova) Y.Meng, comb. nov.(c) 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176, 435-451.