Reassessing the taxonomic diversity of Plagiothecium section Orthophyllum in the North American bryoflora
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Abstract. At the beginning of the twentieth century, Plagiothecium nemorale s.l. and P. succulentum, both belonging to P. sect. Orthophyllum, were considered to be distributed across almost the entire Northern Hemisphere. However, in the mid-twentieth century these taxa were recircumscribed resulting in their exclusion from the North American bryoflora and restricting their distributions to Asia and Europe, and in the case of Plagiothecium nemorale s.l., also North Africa. More recently, it was found that P. nemorale s.l. is a taxonomic complex comprising three distinct species: P. nemorale s.s., P. longisetum, and P. angusticellum. I revised the North American material of P. section Orthophyllum deposited in three herbaria (NY, FH, F) and found that five examined taxa of the section are present in the North America. Two of the species P. angusticellum and P. longisetum, have not been recorded from North America previously, while two others, P. nemorale and P. succulentum, had not been listed in the North American bryoflora for 50 years. One taxon is new for the U.S.A. – P. succulentum f. propaguliferum. Here I provide detailed descriptions of the anatomical and morphological features of the recorded taxa along with photographic documentation of their most important characteristics. I also summarize their known distributions in North America and ecological preferences and provide a key for their identification. Keywords: Taxonomic revision, P. nemorale, P. longisetum, P. angusticellum, P. succulentum.
As science has developed, so has the range of the family Plagiotheciaceae M.Fleisch, as earlier morphological and anatomical studies (Brotherus, 1909; Fleischer, 1912; Jedlička, 1948; Iwatsuki, 1970; Lewinsky, 1974; Buck & Ireland, 1989) have been supplemented by more modern ones based on molecular research (Pedersen & Hedenäs, 2001, 2002; Wynns & Lange, 2014; Wynns et al., 2017; Wynns & Schröck, 2018; Ignatova et al., 2019; Wolski, NowickaKrawczyk, 2020). One of the genera belonging to this family is Plagiothecium Schimp., globally distributed pleurocarpous mosses which are especially widespread in the temperate zone and the tropics (Dierßen, 2001; Ochyra et al., 2008; Wynns, 2015). Jedlička (1948) erected P. sect. Orthophyllum Jedl. in his Monographia Specierum Europaearu, gen. Plagiothecium s. s., within which he included three species: P. Roeseanum (Hampe) Bryol. Eur. [synonym of P. cavifolium (Brid.) Z.Iwats.], Brittonia, XX(X), 2020, pp. 1–14 © 2020, by The Author(s)
P. succulentum (Wilson) Lindb., and P. neglectum Mönk. [synonym of P. nemorale (Mitt.) A.Jaeger]. More recently, Wynns (2015) recognized six species in section Orthophyllum: P. cavifolium, P. cochleatum Dixon, P. japonicum Sakurai, P. nemorale, P. rhizophyllum Sakurai, and P. succulentum. New research on P. nemorale s.l. (Wolski, Nowicka-Krawczyk, 2020) resulted in the restoration of one of it synonyms – P. longisetum Lindb., and the description of a new species, P. angusticellum G. J. Wolski & P. Nowicka-Krawczyk; both are properly placed in sect
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