Brachythecium Moss (Brachythecium plumosum)

Description

Brachythecium plumosum is medium-sized to fairly large, and sometimes forms extensive patches.Main stems are prostrate, but branches are often rather long, more or less erect, and often curved. They are glossy green and often tinged golden brown. The leaves are egg-shaped, rather concave, with a tapering tip, loosely appressed and overlapping,and 2 mm or so in length. They curve slightly to one side, especially at the tip of the shoots, more than in most other Brachythecium species. The single nerve ceases well below the tip. Egg-shaped capsules (1.5-2 mm long) are not uncommon and have a conical lid. The seta is moderately roughened towards the tip and smooth below; this can be observed with a hand lens on mature setae that are not too old or damaged.B. rutabulum (p. 746) usually has more widely spreading leaves that are not curved to one side, and its capsules have a more coarsely roughened seta. B. rivulare (p. 748)has a distinct patch of cells in the basal corners of the leaves that often run down onto the stem. Straight-leaved forms of B. plumosum that are sometimes found on rock faces occasionally resemble B. populeum (p. 744), but differ in their broader leaves with a shorter tip, the nerve ceasing below the tip. Hygrohypnum species (pp. 730-734) also grow by streams and have curved leaves, but usually have flaccid leaves with a shortly pointed or blunt tip and a weak or double nerve. Large forms of H. luridum (p. 731) with a strong nerve and acute leaves may be hard to distinguish in the field unless its narrower, elliptical, curved capsules are present, borne on a smooth seta. See also Platyhypnidium riparioides (p. 758), P. alopecuroides (p. 759), Scleropodium cespitans (p. 754) and Cirriphyllum crassinervium (p. 757).B. plumosum is characteristic of boulders, rock slabs, and the base and roots of trees, often in light shade, by fast-flowing, upland streams and larger rivers in the lowlands,though rarely by sluggish streams. It sometimes occurs away from water, and then usually in smaller quantity, on stones and rocks that are damp and shaded.