Didymodon validus Limpr., Laubm. Deutschl.

Ignatova, E. A., Fedosov, V. E., Kuznetsova, O. I., Fedorova, A. V. & Ignatov, M. S., 2024, On the genus Didymodon s. str. (Pottiaceae, Bryophyta) in Russia, Arctoa 33 (2), pp. 129-155 : 139-140

1. Didymodon validus Limpr., Laubm. Deutschl. 1:

557. 1888. Figs. 5–6 .

Plants medium-sized to large, in dense or loose tufts, olive-green or brownish-green, dull. Stems to 3.5 cm long, erect, simple or branched, with central strand. Rhizoidal tubers absent. Leaves flexuose and incurved when dry, erectopatent to patent whan wet, ovate-lanceolate or linear-lanceolate, narrowly acute, not decurrent, (1.2–)1.6– 2.8× 0.6–0.8 mm, canaliculate distally; margins narrowly recurved in proximal 1/2–3/4, unistratise, entire; costa strong, 45–110 µm wide at leaf base, slightly narrowing upwards, excurrent into short or long mucro, prominent dorsally, flat or weakly convex ventrally, with quadrate, smooth cells on both surfaces, without band of translucent cells on ventral side below apex, in transverse section semicircular, with 4–6 guide cells in 1 layer, ventral stereids in 1–3 layers, ventral epidermis differentiated, with not bulging outer walls, dorsal stereids in 2–3 layers, dorsal epidermis present or absent; lamina unistratose; upper and median laminal cells rounded-quadrate, elliptic and transversely elliptic, 5–15×5–13 µm, with moderately thickened walls, smooth; basal juxtacostal cells rectangular, 12–65×5–12 µm, smooth, moderately thick-walled, chlorophyllose; basal marginal cells not differentiated or slightly shorter. KOH-reaction yellowish-green. Asexual reproduction by round multicellular gemmae born on branched stalks in leaf axils (rarely present in populations from Russia). Apparently dioicous, perigonia not seen. Subperichaetial leaves ca. 1.8× 0.5 mm, with wide bases and subulate acumina; inner perichaetial leaves 1.5× 0.35 mm, from rectangular bases abruptly constricted into triangilar acumina. Setae ca. 1.2 mm, orange-brownish. Capsules ovate-cylindrical, 1–1.5 mm long, brownish. Annuli not seen. Opercula conic, with long beak, ca. 0.8 mm long, cells in spiral rows. Peristome with low basal membrane, teeth 32, ca. 700 µm long, spirally twisted when dry, orange-brown, with oblique ridges and dense, spiculose papillae. Spores 11–16 µm. Calyptrae not seen.

Didymodon validus is widespread in the Caucasus and southern regions of Asian Russia. It differs from other species with unistratose leaf laminae, including margins, and smooth laminal cells, in having larger leaves and acumina longer than bases (from D. mongolicus , D. borealis and D. acutus ) or in shorter excurrent costa and not fragile leaf tips (from described here D. abramovae ).

Figures

Fig. 5. Didymodon validus (from: Russia, Yakutia, Chersky Range, Ignatov & Ignatova 15-1069, MHA9101342, isolate OK3464). A: capsule; B–C: leaf transverse sections; D: mid-leaf cells; E, G: habit, dry; F: habit, wet; H–I:perichaetial leaves; J: basal leaf cells; K: upper leaf cells; L–P: leaves. Scale bars: 2 mm for E– F; 1 mm for G–I; 100 µm for A–D, J–L.

Fig.6. Didymodon validus (from: Russia, Yakutia, Chersky Range, Ignatov & Ignatova 15-1069, MHA9101342, isolate OK3464). A–B: general view of peristome; C–D: tips of peristome teeth; E: basal membrane; F–G: close view if peristome teeth showing ornamentation of their surface. Scale bars: 0.5 cm for A; 100 µm for B; 50 µm for C–D, F; 20 µm for E, G.