Pseudoditrichum mirabile, the only species of Pseudoditrichaceae, has been known for a long time from a single collection from the Canadian Arctic. Its systematic position remained enigmatic due to similarity in gametophyte structure with Ditrichaceae, a family that has simple peristomes, whereas the peristome in Pseudoditrichum is double. Due to this difference, Pseudoditrichum was classified in either Funariales or Bryales. A recent discovery of this species in the Anabar Plateau in northern Siberia has allowed its phylogenetic position to be tested based on plastid rps4 and rbcL and mitochondrial nad5 sequences. The results of this research reject the earlier hypotheses. Instead, the molecular analysis resolves Pseudoditrichum in a clade with Chrysoblastella chilensis (formerly Ditrichaceae) in the haplolepideous lineage. The peristome of Pseudoditrichum is of a previously unknown type with a fully developed exostome and hyaline endostome elements opposite the exostome teeth, based not on the 4:2:4 peristomial formula, but on 4:2:3. Double peristomes of the same type, albeit rather strongly reduced, occur in Catoscopium, Chrysoblastella, Distichium and Ditrichum flexicaule. The polyphyly of Ditrichaceae is confirmed by molecular phylogenetic analysis, and Ditrichum flexicaule and D. gracile are segregated into the new genus Flexitrichum and family Flexitrichaceae. An independent status of the recently resurrected family Distichiaceae is supported, and segregation of Chrysoblastella and Saelania into new monospecific families is proposed.

Haplolepideous moss systematics has been through major changes based on morpho-molecular studies. However, many taxa remain little studied with still unclear circumscriptions and relationships among the traditionally recognized families. We inferred the phylogenetic relationships of the haplolepideous mosses based on a sample of 37 out of the 38 haplolepideous moss families and using mitochondrial (nad5 G1 intron) and chloroplast (trnS-rps4 spacer/rps4 gene and trnL gene/trnL-trnF spacer) markers. The resolved relationships indicate the need for rearrangements in the circumscription of the Aongstroemiaceae and Dicranellaceae and their genera, which correspond to the variation of morphological characters of leaf shape, rhizoid tuber morphology, and capsule and peristome traits. The two families, although historically considered morphologically close, were resolved as separate lineages in the core haplolepideous clade. The genera Aongstroemia and Dicranella were resolved as polyphyletic across the clades corresponding to the families Aongstroemiaceae and Dicranellaceae and other clades. The characterization of Aongstroemia by julaceous plants is not supported; the three species sampled here belong in three separate families and differ from one another in other (more stable) characters, such as the presence and shape of peristome teeth. Regarding Dicranella, the sampling of 13 of its 167 species suggests the broad morphological variation comprised by the genus under its current circumscription might be narrowed down to smaller ranges corresponding to the phylogenetically separate clades. The present molecular data furthermore suggest changes in the composition of the protohaplolepideous Dicranidae grade, including one Dicranella clade, a new lineage with a ditrichoid morphology, but excluding the Chrysoblastellaceae, which were resolved in the core haplolepideous clade. The latter finding implies the independent evolution of the rare double-opposite peristome type in both the protohaplolepideous grade and the core haplolepideous clade. Keywords haplolepideous mosses; nad5 G1 intron; polyphyly; phylogenetics; trnS-trnF Supporting Information may be found online in the Supporting Information section at the end of the article.

A revision of the complex of Plagiothecium laetum and related species revealed a neglected species in East Europe, with some localities in Russian Far East, Plagiothecium rossicum. It differs from West European and North American P. laetum in sequences of both nuclear ITS and chloroplast rpl16 and in morphology. Plants identical with West European P. laetum occur in Russia only in the Black Sea coastal area of Caucasus and one locality in lowland European Russia (Kaluga Province). Asiatic plants characterized by abruptly tapered leaves with more or less piliferous acumen are referred to P. svalbardense, which therefore appeared to be a common plant throughout Siberia and Russian Far East. Plagiothecium curvifolium is also distinct from P. rossicum, in both DNA sequence and morphology; it is not confirmed by molecular markers in Russia east of the Urals. Резюме Ревизия комплекса видов, близких к Plagiothecium laetum, выявила ранее не распознанный вид, довольно широко распространенный в лесной зоне Восточной Европы, и с рядом местонахождений на Дальнем Вотоке России, Plagiothecium rossicum. Он отличается от западноевропейского и североамериканского P. laetum s.str. по последовательностям ядерных (ITS) и хлоропластных (rpl16) участков ДНК, а также по морфологии. Растения, идентичные западноевропейскому P. laetum, были найдены в России только в районе черноморского побережья Кавказа и в одном местонахождении в Калужской области. Азиатские растения с относительно быстро суженным у верхушки листом, часто выглядящие как имеющие гиалиновый волосок, отнесены к P. svalbardense, который, таким образом, оказывается частым видом в Сибири и на Дальнем Востоке. Plagiothecium curvifolium имеет четкие отличия от P. rossicum и по каждому из изученных молекулярных маркеров, и по морфологии; он не был найден в России восточнее Урала.