Hymenostylium xerophilum, sp. nov., and H. gracillimum, comb. nov., two neglected European mosses and their molecular affinities

Abstract

Hymenostylium xerophilum is described as a new species from the European Alps. Molecular rps4 and ITS data support its recognition and elucidate its affinities to other species of the tribe Pleuroweisieae. It is closely related to H. gracillimum, comb. nov., which is based on the old and neglected Gymnostomum gracillimum, which replaces the recent name G. boreale. Both species share non-coloured to pale yellowish-brown rhizoids, stem central strand and indistinct sclerodermis, keeled leaves, and concave laminae in abaxial view. They differ from each other in leaf shape and several essentially quantitative characters. Sporophytes have never been found in H. xerophilum, but they are known from several localities in H. gracillimum. The former colonizes rather dry, sunny to half-shaded calcareous rocks, whereas the latter needs moist and shaded rock habitats and shows a preference for subneutral slate. At present, H. xerophilum is known only from the Alps (Austria, and a single site in Germany), where it is rather widespread in calcareous regions. H. gracillimum seems to be a distinctly rarer plant, to date known only from eight Austrian sites and one locality in Russian Karelia. Other published records under the name G. boreale have been wrongly attributed to this species. Lectotypes are designated for G. gracillimum and Gyroweisia acutifolia. A key to Hymenostylium and the genera of Pleuroweisieae in Europe is presented.

Thicker rhizoids of both species are covered with a thick, non-coloured protective layer and filled with oil-droplets and leucoplasts. They represent a subterranean secondary protonema, which plays an important role in the survival and propagation of these mosses, vital especially in the case of the non-sporulating H. xerophilum.

Keywords:

• Gymnostomum
• Pleuroweisieae
• Pottiaceae
• Taxonomy
• Phylogeny
• ITS
• rps4

We are grateful to P Sollman for valuable information and the provision of some literature. Thanks are also due to C Schmidt and M Ahrens for their opinion on early collections of the new species. R Skrypczak is acknowledged for arranging the loan of type material from AUT, and fruitful discussions and translations from French. C Scheuer is thanked for providing the Latin diagnosis and arranging loans to Graz. Lastly, we thank T Hallingbäck, E Ignatova, L Meinunger, G Schlüsslmayr, and the curators of BM, DUKE, E, MHA, MUB, MW, PR, S, and W for sending specimens, and the curators of GJO, GZU, and KL for access to the bryophyte herbaria. The molecular analyses were supported by a grant from the Ministry of Education of the Czech Republic (grant no. MSM 6007665801).

Taxonomic Additions and Changes: Hymenostylium xerophilum Köckinger & J.Kučera, sp. nov.; Gymnostomum gracillimum Nees & Hornsch., lectotype designated; Hymenostylium gracillimum (Nees & Hornsch.) Köckinger & J.Kučera, comb. nov. (Gymnostomum calcareum var. gracile Breidl. ex G.Roth, syn. nov.; Gymnostomum boreale Nyholm & Hedenäs, syn. nov.); Gyroweisia acutifolia Philib., lectotype designated.