Engellaria (Caryophyllaceae), a new North American genus segregated from Stellaria

Abstract

Background and Aims: Stellaria traditionally comprises 150-200 species, mainly distributed in the temperate regions of Eurasia and North America. Molecular studies demonstrated that Stellaria is polyphyletic and includes about 120 species. The genus has a high phenotypic variability which has led to nomenclatural disorders, making the identification of the various species difficult. A note is presented about a taxon currently accepted under the genus Stellaria -Stellaria obtusa- which should be recognized as a separate genus, here proposed as Engellaria gen. nov.Methods: This study is based on examination of specimens of American and European herbaria and analysis of relevant literature.Key results: Available molecular data show that Stellaria obtusa is not included in the Stellaria s.s. clade, but instead is basal to another clade comprising the genera Honckenya, Schiedea, and Wilhelmsia. Stellaria obtusa was, therefore, compared with these three groups and with morphologically similar apetalous members of Stellaria s.s. (S. crispa, S. media, S. pallida, and S. irrigua). The results obtained lead to the recognition of S. obtusa as a separate new North American monotypic genus. A diagnostic key of the apetalous members belonging to the American Caryophyllaceae genera is proposed. Finally, the names Stellaria obtusa and S. washingtoniana (= S. obtusa) are lectotypified based on specimens deposited, respectively, at UC (isolectotypes at GH, NY, and YU) and GH (isolectotypes at BM, CAN, CAS, CS, DOV, F, GH, K, MIN, MSC, NY, US, and VT). For the name Alsine viridula (= S. obtusa) the holotype was found at US (isotypes at CAS, F, GH, NY, OSC, RM, and UC).Conclusions: Stellaria obtusa does not belong to the genus Stellaria. The present study shows that the combined use of morphological data and phylogenetic analyses helped to clarify the taxonomic position of difficult plant groups, as in Stellaria.