Ditrichum Moss

When sterile, Ditrichum pusillum is morphologically very similar to D. ambiguum and D. tortuloides. When sporophytes are present, the dense, fine, obliquely striate peristome teeth with weak papillae immediately distinguish D. pusillum from those two species, which have spiculose peristome teeth. The spores of D. pusillum (10-19 µm) are also larger compared to those of D. ambiguum (6-11 µm) and D. tortuloides (9-13 µm). A discussion of the relationships of D. pusillum with both D. ambiguum and D. tortuloides was given by R. R. Ireland and H. Robinson (2001).

Plants small, 0.7–1.0 cm high, yellowish green or brown, in loose tufts. Stems erect, simple or sparsely branched. Leaves appressed when dry, erect-patent when moist, lanceolate, 2.0–2.3 mm long, gradually narrowed from an ovate base to a slender acumen; margins reflexed or revolute below, plane above, entire throughout; costa stout, shortly excurrent; cells rectangular, thin-walled, 10–20 µm × 3–5 µm at the shoulder, 13–26 µm × 5–10 µm at the margins, the upper ones shorter. Dioicous. Setae straight, 5.0–7.0 mm long, yellowish brown, sometimes twisted above; capsules erect, oblong-ovoid, symmetric, ca. 2 mm long, smooth when dry; opercula short conic-rostrate; annuli in 2 rows of large and thick-walled cells; peristome teeth linear, ca. 0.2 mm long, divided nearly to the base, papillose, whitish yellow above, yellowish brown below. Spores 16–18 µm in diameter, yellowish brown, irregularly papillose.

Plants small, to ca. 1 cm, forming dull green tufts. Stems 0.4-1.2 cm, simple. Leaves to ca. 3.5 mm, erect-patent, weakly secund, lanceolate to linear-lanceolate, gradually acuminate to a channelled subula, acute, lamina 1-stratose except on margins; margins bistratose, entire or serrulate near the apex, irregularly thickened and recurved at least in distal half; costa stout, percurrent to excurrent, in section with abaxial stereid band; proximal lamina cells elongate-rectangular, distal lamina cells subquadrate to short-rectangular or somewhat irregular in outline, ± incrassate. Specialized asexual reproduction by rounded to pyriform or irregularly-shaped, yellow to orange rhizoidal tubers, to 150 µm. Sexual condition dioicous; perichaetial leaves similar to stem leaves but with a somewhat longer subula narrowing more abruptly from the base. Seta becoming reddish with age, to 1.5 cm, erect. Capsule erect, dark brown to reddish brown, ovoid to cylindrical, symmetric, 1-2 mm, smooth to ± furrowed when dry; operculum obliquely conic-rostrate, blunt, 0.3-0.7 mm; peristome split nearly to the base into 2 segments, brown, densely and finely obliquely-ridged and lightly papillose, 200-250 µm. Spores 11-20 µm, appearing ± smooth.

Distribution: China, Russian Far East, Europe, North America, and Africa.

Habitat: on wet soil or rocks.

Ditrichum microcarpum Broth. in Handel-Mazzetti, Symb. Sin. 4: 12. 1929. Type. China: Yunnan, Handel-Mazzetti 6264 (holotype H). Ditrichum setschwanicum Broth. in Handel-Mazzetti, Symb. Sin. 4: 12. 1929. Type. China: Sichuan, Yen-yuan Co., Handel-Mazzetti 2859 (holotype H; isotype MO). Ditrichum tortile (Schrad.) Brockm., Arch. Ver. Freund. Naturg. Mecklenburg 23: 74. 1870. Ditrichum pusillum var. tortile (Schrad.) I. Hag., Kongel. Norske Vidensk., Selsk. Skr. 1910 (1): 50. 1910. Trichostomum tortile Schrad., Bot. Zeitung (Regensburg) 1: 74. 1802.

Didymodon pusillum Hedwig, Sp. Musc. Frond., 104. 1801; Ditrichum tortile (Schrader) Brockmuller; Trichostomum tortile Schrader; T. tenue Hedwig; Weissia capillacea Bridel

Ditrichum pusillum (Hedw.) Timm, Fl. Megapel. 216. 1788
Trichostomum pusillum Hedw. Descr. 1: 74. 1787. Mnium tortile Schrad in J. F. Gmcl. Syst. Nat. 2: 1328. 1791. Trichostomum tortile Schrad. Samml. Krypt. Gew. 1: 12. 1796. Trichostomum tenue Hedw. Sp Muse. 107. 1801. Leptotrichum pusillum Hatnpe, Linnaea 20: 74. 1847.
LepMrichum tortile C. Mull. Syn. 1: 454. 1848.
Ditrichum tortile Brockm. Laubm. Meckl. 74. 1869.
Leptobcrbula berica Macoiin, Cat. Can. PI. 6: 49. 1892. Not L. berica Schimp. 1876.
Plants variable in size and development, yellowish-green or black when old, gregarious; stems mostly simple, erect, 1-2 cm. high ; branches subapical : leaves small, erect and lanceolate on the branches, often twisted, spreading or reflexed on the main stems, 1-3 mm. long; margins plane or revolute, often doubly serrulate; costa broad, percurrent or excurrent into a subulate point, channeled and denticulate at the apex; basal cells oblong, clear, the upper ones rectangular w^ith thick walls; perichaetial leaves longer and broader at the base, not sheathing, the point subulate. Dioicous : antheridia terminal on plants about 1 cm. high : seta variable in length from 5-15 mm., red, twisted: calyptra cucuUate: capsules very variable in size, 0.51.5 mm. long, ovoid to cylindric; walls of rectangular irregular cells; neck short, stomatose; lid conic-rostrate, bordered; annulus single, small, falling in fragments; peristome red, the basal membrane short, the teeth bifid, papillose, slightly twisted or erect, their joints thick: spores smooth, yellow, 10-14 m in diameter, maturing in autumn.
TvPE locality: Leipzig, Germany.
DiSTRiBUTio.s': Common on clay and sandy banks, in ditches and pits, and along roadsides, from Newfoundland to Ontario, and south to Florida and Louisiana; doubtfully reported from California; also in Europe. Asia, and Africa.