Rhachithecium perpusillum (Thwaites & Mitt.) Broth., Nat. Pflanzenfam.

Chantanaorrapint, Sahut, Sevanakun, Nilobon, Suwanmala, Orawanya, Sukkharak, Phiangphak, Printarakul, Narin & He, Si, 2021, The moss family Rhachitheciaceae (Dicranales, Bryophyta) in Thailand, Phytotaxa 520 (3), pp. 279-284 : 283

Rhachithecium perpusillum (Thwaites & Mitt.) Broth., Nat. Pflanzenfam. 1(3): 1199. 1909. ( Fig. 2 )

≡ Zygodon perpusillus Thwaites & Mitt., J. Linn. Soc., Bot. 13: 303. 1873.

Type: — SRI LANKA (Ceylon). Central Province , s.d., G.H.K. Thwaites 77 (lectotype NY (NY01244129 photo seen) designated here; isolectotype BM000982081, BM000982082, PC-PC0075037) .

Plants up to 4.5 mm high (including sporophytes), green to yellowish green, growing in loose to dense tufts. Rhizoids pale brown to reddish, clustered at stem base. Stems erect, usually simple, rarely branched, in cross section 7–11 layers of cells across, 140–190 µm in diameter, composed of a cortex and a central stand; cortical cells large, thick-walled, 2–4 rows of cell; central stand cells, small, thin-walled. Axillary hairs uniseriate, consisting of 4–6 cells vertically, 160–250 µm long, colorless. Leaves appressed to flexuous when dry, erecto-patent when moist, lingulate to oblong-spathulate, 0.8–1.7 mm × 0.3–0.5 mm; apex acute to obtuse; margin entire, plane or partly recurved; costa single, ending below leaf apex, 4/5–6/7 the leaf length; median and upper laminal cells hexagonal-round to rectangular or quadrate, 7.5–32.5 × 7.5–20 µm, smaller towards margin, smooth, moderately thick-walled; lower laminal cells rectangular to elongatepentagonal, 35–98 × 12–25 µm, narrower towards margin, hyaline, thin-walled. Asexual reproduction not seen.

Autoicous. Perigonia lateral on short branches; perigonial leaves ovate, convolute, 0.3–0.5 mm long, apex acute, margin entire; antheridia ca. 8 per perigonium; paraphysis absent. Perichaetia terminal; perichaetial leaves lanceolate, convolute, 1–1.7 mm long, apex acute, margin entire or slightly crenulate near apex; paraphysis present. Vaginula elongate, 0.3–0.7 mm long. Seta green to greenish brown, (0.7–) 1.3–1.7 mm long, smooth, somewhat erect. Capsule greenish brown to yellowish brown, erect, symmetrical, ovoid to cylindrical, (0.3–) 0.5–0.75 mm long, (0.2–) 0.3–0.45 mm in diameter, sulcate when dry; exothecial cells rectangular to elongate-hexagonal, thin-walled, 27–53 × 15–43 µm. Annulus composed of a row of hyaline cells. Operculum short-conical. Peristome single, 16 teeth fused into 8 pairs, pale brown, lanceolate-triangular, with transversely striolation, inserted at the mouth. Spores pale brown, spherical, finely papillose, 22–33 µm in diameter. Calyptra cucullate, glabrous in lower part, scabrous in upper part.

Habitat and ecology: —In Thailand, Rhachithecium perpusillum was found on tree trunks in lower montane and pine-oak forests between 850 and 1900 m.

Distribution: —Widely distributed in Africa ( Burundi, Central Africa, Guinea, Madagascar, Malawi, Nigeria, Tanzania, Transvaal, Zaire, Zambia, and Zimbabwe), extending to Asia ( Sri Lanka, China, and Thailand) and central and south America ( Mexico, along the Andes, and Brazil) ( Gangulee 1976; O’Shea 2006; Xiong 2001; Fischer et al. 2006; Printarakul et al. 2012).

Specimens examined: — THAILAND. Chiang Mai; Chiang Dao Wildlife Sanctuary, 1,160–1,900 m, 11 March 1995, D. Allen Y88 (CMUB), 18 December 2011, N. Printarakul 5114 (CMUB), 11 November 2016, S. He & S. Chantanaorrapint 47717a ( MO, PSU), S. Chantanaorrapint & O. Suwanmala 630 ( PSU), 26–27 October 2017, S. Chantanaorrapint & O. Suwanmala 1786, 1858 ( PSU), 27–28 January 2018, S. Chantanaorrapint & O. Suwanmala 3176, 3212 ( BKF, PSU); Doi Suthep-Pui National Park , 850–1685 m, 15 October 1988, J.F. Maxwell B-71 (CMUB), 29 October 2008, N. Printarakul 301 ( CMUB, SING), 30 May 2010, N. Printarakul 3021 (CMUB), 18 June 2011, N. Printarakul 4013 (CMUB) .

Notes: — Rhachithecium perpusillum was described based on Thwaites’ collection from Ceylon ( Sri Lanka). In the protologue, Mitten (1909) did not point to single specimen conserved in one herbarium, therefore, it becomes necessary to designate a lectotype. We here designate Thwaites’s collection (Thwaites 77) in NY (NY01244129) as the lectotype of R. perpusillum (≡ Zygodon perpusillus ).

Figures

FIGURE 2. Rhachithecium perpusillum (Thwaites & Mitt.) Broth.: A. Habit when dry. B. Habit when moist. C. Cross section of stem. D. Axillary hairs. E–I. Leaves. J. Leaf apex. K. Median laminal and marginal cells. L. Basal laminal and marginal cells. M. Cross section of costa. N. Perigonial leaf. O. Perichaetial leaf. P. Exothecial cells of capsule. Q. Peristome. Drawn by O. Suwanmala, all from S. Chantanaorrapint & O. Suwanmala 630 (PSU).