Rhacomitrium nigritum

Rhacomitrium nigritum

Rhacomitrium nigritum Jaeg., Ber. S. Gall. Naturw. Ges. 1872–1873:90, 1874 (Ad. 1:368).

Grimmia nigrita C. Müll., Syn. 1:801, 1849, hom. illeg. [Original material: Hermite Isl., Tierra del Fuego, coll. J. D. Hooker, 1839–1843.]

Plants blackish green, stems unbranched to sparsely dichotomously branched, to 5 cm high. leaves broadly lanceolate, 2.5–3.0 mm long, 1 mm wide, usually appressed-imbricate with occasionally recurved tips when dry, stiffly spreading when wet; margins entire; base only slightly plicate with broadly and laxly recurved margins; apex concolorous with few or no elongate cells; costa percurrent, very stout, 125–200 μm wide at base, ca. 100 μm wide near tip; lamina cells smooth; upper cells 5–12 μm long, mostly 1–2 times as long as wide, bistratose, sometimes tristratose at margin; inner and lower cells unistratose; lower cells to 75 μm long, lumens as wide as nodulose or sinuous walls; alar cells short, smooth, to 20 μm broad, in short-decurrent cluster of 3–5 rows; only 1–2 less thickened cells extending up the margin. Setae 5–7 mm long, yellowish brown when mature, blackish when old. Spores 15–22 μm in diameter.

MAS AFUERA: Correspondencia, 1100 m, Sk. 132; Los Innocentes, near summit, 4500–5000 ft. H. & E. 94.

The distribution of the species has been given as Tierra del Fuego, South Georgia, and Kerguelen; however, material must be rechecked. Earlier descriptions and treatments did not make any mention of either costa width or cross section of leaves, characters of primary importance. Dixon (1913–1929) and others who follow him place the name with R. rupestre under the broad concept of R. crispulum. What Dixon saw and whether it included material of the above description is unknown. In any case, neither Dixon nor Clifford (1955) seems to have made any allowances for any distinct species of this type in the subantarctic region, and such a view must be corrected.

The concept followed here is based on the key and description by Roivainen (1955). The Roivainen treatment is sufficiently detailed to allow one to disagree intelligently. Unfortunately, the treatment does not indicate whether types or other authentic material of R. nigritum or R. subnigritum (C. Müll.) Par. were seen. The original descriptions of the two species are useless. Brotherus (1924) cited and distributed the Skottsberg material from Juan Fernandez as R. subnigritum. Roivainen reserves that name for specimens with thicker borders (4-stratose) and includes R. limbatum Bartr. as a synonym. If the setae mean anything, those of the Juan Fernandez specimens are longer and darker as described for R. subnigritum rather than very short and yellow as originally described for R. nigritum.