Najas L. (Hydrocharitaceae) is a cosmopolitan genus of aquatic plants that was established by Linneaus) and subsequently split into Najas and Caulinia Willd. by Willdenow at generic level. However, various sectional classifications proposed in subg. Caulinia have been controversial.
Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and their Japanese collaborators conducted molecular phylogenetic analyses to reconstruct biogeographic history and infer the ancestral state ploidy level.
By significantly expanding the taxon samplings to cover much of the taxonomic, morphological and geographic variation within the genus, the researchers aimed to critically re-assess infrageneric classification, biogeography and polyploid evolution in Najas using a phylogenetic framework.
Their analyses of plastid and nuclear (ITS) DNA datasets produce largely congruent results that recover the two subgenera but find little support for most sectional classifications. The phylogenies recovered from the two datasets were largely consistent, comprising two lineages corresponding to Najas subg.
To overcome the shortfall, the researchers proposed a new sectional classification of subg. Caulinia. The previously inferred tropical Asian origin of the genus was rejected and, instead, North America was discerned as the ancestral area, implicating dispersal of the most recent common ancestor of Najas and its sister genera in Hydrocharitaceae from tropical Asia.
The researchers presented a revised key to Najas subg. Caulinia sect. Americanae and sect. Caulinia, sectional descriptions and type designations, based on their findings and the insights provided by previous botanists.
The study entitled “Phylogeny of Najas(Hydrocharitaceae) revisited: Implications for systematics and evolution” has been published in Taxon.