Grimmiaceae. Genus Dilutineuron

1. Costa reaching half-leaf length or shortly above; leaf apex flexuose when dry to strongly so — 3. D. corrugatum

The species is sporadically distributed in mountain areas of Eastern Siberia (Western Sayan Mts and Transbaikalia) and in southern Kamchatka, Commander Islands, Sakhalin and Kuriles; it rarely penetrates in the Arctic, being collected twice in the lower course of Lena River (Yakutia). Its long and wavy, serpent-like leaf apices in combination with costa ending at about mid-leaf are sufficient for its easy recognition.

— Costa to 3/4-5/6 leaf length; leaf apex not or only slightly flexuose — 2
2. Leaf lamina distally bistratose in 1-5 rows along the leaf margin; distal laminal cells square to short rectangular — 2. D. brevisetum

Rather frequent in the Primorsky Territory, on Kamchatka, Sakhalin and in the Kuril Islands, also known from few localities eastward, in the Khabarovsk Territory and Amurskaya Province; grows both on wet and rather dry rocks, sometimes being abundant, from forest to tundra belt. Important diagnostic characters of D. bre­visetum include irregular branching, partially bistratose distal leaf lamina, short upper laminal cells and often denticulate margins near leaf apex. It is also rather frequently fruiting plant, contrary to other species of the genus.

— Leaf lamina unistratose throughout, distal laminal cells rectangular — 1. D. fasciculare

Rather common in Kola Peninsula, sporadic in Karelia and Leningrad Province, known from few localities in NE European Russia, North and Subpolar Urals, then in Asian Arctic (Severnaya Zemlya and Vrangel Island) and becoming more frequent in northern Russian Far East, from Chu­kotka to Kamchatka and Magadan Province, found also in Commander and Kuril Islands and Khabarovsk Territory. Numerous short lateral branches, long costa, unistratose lamina and elongate distal laminal cells are important for its identification.