Fabronia pusilla Raddi, Atti Accad. Sci. Siena

Fabronia pusilla Raddi, Atti Accad. Sci. Siena View in CoL 9: 231. 1808.

Type. Europe: Toscana, Raddi s.n.

Illustrations: Figs. 9 View Fig : 1–6, 10: 1–5 & 11: 11–13; see also Ignatov & Ignatova (2004), Fig. 430 on page 648.

Plants very small, soft, yellowish green, glossy, in small dense tufts. Stems creeping, ascending at apex, irregularly branched; branches erect, 1–2 mm long, densely foliate. Leaves loosely appressed when dry, often with recurved piliferous acumen, occasionally slightly secund, spreading when moist, ovate, abruptly long acuminate, 0.50–0.80 u 0.15–0.35 mm; leaf margins coarsely dentate to ciliate, marginal teeth unequal, large 3–5-celled teeth alter with small unicellular teeth; costa slender, smooth, ending at mid-leaf; lamina smooth, upper and median laminal cells rhomboidal, 25– 30(–45) u 9–11 µm, with length/width ratio 3–4:1 and cell length, µm/ leaf length, mm ratio 31.8–49.6; apical leaf cell to 110 µm long; alar cells quadrate to short-rectangular, forming weakly delimited rectangular goup 3–4 cells wide and 6–11 cells along leaf margin. Autoicous, sporophytes infrequent. Perigonia bud-like. Perichaetial leaves ca. 0.5 mm long and 0.2 mm wide, with oblong base and gradually attenuate narrow acumen; costa ending at midleaf; margins moderately dentate in upper part. Sporophytes single in perichaetium. Seta 2–3 mm long, straight, yellow. Capsule ovate, with short neck, 0.4–0.6 mm long and 0.3– 0.4 mm wide, smooth, light brown, concolorous at rim; annulus absent. Peristome single, consisting of 16 exostome teeth fused in pair, light brown, obtuse, ca. 75 µm long; outer surface papillose-striolate, inner surface with less prominent ornamentation, with low vertical ridges. Spores 12– 14 µm, brownish, papillose.Operculum low conic, with short oblique beak or mammillate.

Distribution and ecology. Main distribution area of Fabronia pusilla is in the western parts of Eurasia and North America, with southernmost localities in Mexico, and in northern Africa. It was also reported from southwestern provinces of China and states of Middle Asia. In Russia it is known from two localities: in Rostov Province (south of European Russia) and in Republic of Buryatia (Asian Russia, Baikal Lake area). Both places are characterized by xeric conditions. In Rostov province F. pusilla was collected on dead wood in the park. In Buryatia it grew on the shore of Baikal Lake (Svyatoi Nos peninsula), in deep shady niches of dry cliffs, on eroded rock surface. In the main part of its area, F. pusilla grows mainly on dry rocks (volcanic, granite, limestone), but is occasionally collected from tree trunks (e.g., of Quercus pubescens ).

Specimens examined: RUSSIA: EUROPEAN RUSSIA: Rostov Province: Rostov-na-Donu, Kamenka Settlement, park of the health resort “Rostovsky”, 16.X.2000, Sereda s.n. ( MHA); ASIAN RUSSIA: Republic of Buryatia: NE shore of Baikal Lake, Svyatoi Nos peninsula, 450 m alt, 26. VI.1956, Bardunov s.n. ( LE).

EUROPE: SPAIN: Granada, Sierra Nevada, Güejar Sierra, Vereda de la Estrella, 145 m alt., 21. V.2009, Guerra 30176 ( LE); Andalucia, Grazalema, Sierra del Endrinal, 350 m alt., 3. V.2015, Kučera 17500 ( CBFS). ITALY: South Tyrol: Etschtal, Castel Feder S of Auer, 350 m alt., 29.X.1989 Köckinger s.n. ( MW, ex Herb H. Köckinger); prope Bozen, 260 m alt., Sauter, Flora Exsiccata Austro-Hungarica #717 ( LE). SWITZERLAND: Ticino, Lugano, 280 m alt., 11.II.2003, Schnyder 2003001 ( MW, ex Herb. Norbert Schnyder). AUSTRIA: Styria orientalis, Hartberg, 450 m alt., X.1942, Baumgartner, Crypt. Exs. ed. a Museo Hist Natur. Vindobonensi #892 ( LE).

ASIA: TADJIKISTAN: Darvaz Ridge, Pyandzh River basin, Egit Village, Surkh-Dara gorge, 1130 m alt., 9.VII.1964, Mamatkulov 5218 ( LE). KYRGYZSTAN: Kyrgyz Range, Dzhirly-Kaindy stow, 1900 m alt., 18. VI.1965, Rakhmatullina s.n. ( LE).

NORTH AMERICA: U.S.A.: Colorado, Boulder Co., Nordseite des Boulder Canyon, 2150 m alt., 30.III.1957, Weber, Crypt. Exs. ed. a Museo Hist Natur. Vindobonensi #4476 ( LE); California: Mariposa Co., Elephant Rock, ca. 975 m alt., 2.XII.2006, Shevock 29285 ( NY); San Benito Co., ca. 470 m alt., 12.II.2005, Shevock 26293 ( NY); Monterey Co., San Antonio Reservoir County Recreation Area, ca. 240 m alt., 3. I.2009, Schevock 32581 ( NY); Oregon: Wheeler Co., John Day River basin, 655 m alt., 23.III.2008, Shevock 31600 ( NY); Wasco Co., Colombia River Gorge National Scenic Area, 45 m alt., 27.III.2008, Shevock 31659 ( NY).

Differentiation. ‘Typical’ specimens of Fabronia pusilla are easily recognized due to large, multicellular teeth at leaf margins. However, some specimens with smaller, 2–3-celled teeth may be referred either to F. pusilla or F. ciliaris (as it is proved by DNA data) and cannot be identified with confidence. Such specimens were observed mainly in Central Europe where both species co-occur. Maybe slightly smaller spores of F. pusilla , 12–14 vs. 15–17 µm in F. ciliaris , can help in these difficult cases.