Weissia exserta (Broth.) P.C. Chen, Hedwigia

Weissia exserta (Broth.) P.C. Chen, Hedwigia View in CoL 80: 158. 1941. – Astomum exsertum Broth., Hedwigia 38: 212. 1899. – Hymenostomum exsertum (Broth.) Broth., Die Natürlichen Pflanzenfamilien I (3): 386. 1902).

Fig. 1 View Fig , 2.

Plants in loose tufts, yellow-green to brownish. Stems 2.0– 3.5 mm long, simple or branched, with well developed central strand and cortical cells very weakly delimited from underlying parenchimatose cells, with a little smaller lumens and thicker cell walls. Leaves loosely contorted when dry, spreading when wet, 1.2–1.8× 0.25– 0.4 mm, widest a little above base, ovate-lanceolate in lower part of stem, gradually becoming longer distally, upper leaves lanceolate to linear-lanceolate, acute to short acuminate, strongly concave distally, with cucullate apices; margins entire, flat or narrowly incurved distally; costa strong, 1/6–1/7 of leaf base width, 50–60 µm wide at base, yellowish to brownish, shortly excurrent as a brownish mucro, with two stereid bands divided by 4–5 guide cells, and papillose ventral epidermis; lamina unistratose, upper laminal cells 6–13×8–10 µm, subquadrate to hexagonal, transverse-rectangular or irregular in shape, thin-walled, with numerous low, massive papillae, 4–8 per cell; basal cells (12–)15–32(–40)×9–15 µm, rectangular, moderately thick-walled, smooth, hyaline to yellowish, translucent, gradually becoming shorter distally, or abruptly becoming quadrate in midleaf, boundary between smooth basal leaf cells and papillose distal leaf cells straight or V-shaped, papillose upper leaf portion occupies ca. 2/3 of the total leaf length. Autoicous, sporophytes abundant, single per perichaetium. Perichaetial leaves with somewhat wider base and longer distal portion, acute to short acuminate. Setae (1.2–) 1.5–2 mm, cygneous when capsules are mature, rarer flexuose, pale. Capsules exserted, cleistocarpous, 0.6–0.8 mm long, elliptical, pale; exothecial cells isodiametric, moderately thick-walled. Annuli partly differentiated. Opercula partly differentiated, not dehiscent, with long, oblique beak. Spores 21–25 µm, brownish, verrucose. Calyptrae ca. 1 mm, cucullate.

Specimens examined: RUSSIA: Buryatia Republic, East Sayan Mountains, Tunkinsky Distr. , “Tunkinskaya valley” National Park , vicinity of Mondy settl., 51.681617°N, 100.975603°E, 1363 m alt., open steppe community, 11.VII.2023, Fedosov ( MW) GoogleMaps . Altai Republic, Ongudai Distr. , ca. 50°30’N, 86°35’E, 1500 m alt., rock outcrops on the mountain eastwards of Malyi Yaloman settl., 4.VIII.2000 Ignatova ( MW9069723 ) GoogleMaps . Krasnoyarsk Territory, Taimyrsky Municipal Distr., 70.9978°N, 102.699°E, ca. 50 m alt., Kysyl-Khaya calcareous rock outcrops on the right bank of Kotuy River , on loamy ground, 14.VII.2005 Fedosov 05-500 ( MW9069724 ) GoogleMaps .

Distribution. Weissia exserta was described from Japan; it occurs in Honshu, Shikoku and Kyushu ( Inoue & Tsubota, 2017). Also, this species is believed to be widespread in China excepting its poorer sampled NW provinces, and also occurs in India ( Li et al., 2001). Howev- er, an affinity between Chinese plants assigned to W. exserta and Japanese specimens has not been so far tested with molecular markers. Thus, this question, as well as an identity of Russian material needs in specially focused study with wider sampling in many lineages of Asian Weissia . Several findings made in the vicinity of Mondy settlement, such as Indusiella thianschanica Broth. & Müll. Hal. , Jaffueliobryum latifolium Lindb. & Arnell ex Thér. , and Aongstroemia julacea (Hook.) Mitt. , represent predominantly Central Asian phytogeographical element that agrees with dry continental climate of Mondy Settlement area. However, Aongstroemia julacea (= A. fuji-alpina (Takaki) Takaki) is also known from Japan, thus further phytogeographical implication would better based on integrative floristic approach ( Fedosov et al., 2022).

Differentiation. Morphological circumscription of W. exserta accepted here in accordance with Brotherus (1899), Noguchi et al. (1988), and Inoue & Tsubota (2017) is based on combination of exserted cleistocarpous capsules with partly differentiated annuli and opercula with long oblique beaks. In possessing setae remarkably longer than capsules and long beak, it differs from all other cleistocarpous species of the genus Weissia .