Acrocarps with hair-points

(If you need to know what an Acrocarp is, click here)
For a full key to Grimma species, see here.

1 Leaves long. 6-9 mm very narrow with silver-white hair points (the hairs can fall off, and they are absent from younger leaves); plants looking like patches of dark green or black velvet on moorland (associated with Sphagnum) or wet rock ledges in west Britain — Campylopus atrovirens.

Leaves shorter; plants not as above — 2

2 Generally on trees, stumps or wooden palings (can also be on stone)— 3

On some other substratum  — 4

3 Dull green; leaves tapering into wide bases of hair-points; capsule scarcely raised above leaves. Glass hair difficult to see in young plants. Mainly on stone but also on willow, elder or poplar (if epiphytic often grows with O. affine) —Orthotrichum diaphanum.

Bright green; narrow hair-point projects from middle of broad leaf apex; capsule on evident seta. Looks like T. muralis (is occasionally on walls) but that species has inrolled margin until the top of the leaf —Tortula laevpila

4 On sand dunes (sometimes stone or thatch); plants bright golden-green to orange-brown when moist:

Glass hair comes our of leaf straight —Tortula ruraliformis (= T. ruralis var ruraliformis = Syntrichia ruralis var arenicola)

Glass hair comes out of the leaf at an angle— T. calcicolens = Syntrichia ruralis var calcicola

Some other habitat — 5

5 Growth form straggling; stems freely branched; extensive patches formed — 6

Forming neat tufts or cushions; stems little branched (mostly simple or merely forked) — 8

6 Very robust; grey-green with wispy white tips forming mats, 20 cm. to 1 m. or more across; on peat or rock (individual stems often 12-25 cm. long); mountain tops — Rhacomitrium lanuginosum (=Racomitrium lanuginosum)

 Much more slender, in loose tufts or thin straggling patches a few centimetres across, on rock (individual stems 2-8 cm.) — 7

7 Stems slender, elongated; shoots pale greyish green with conspicuous white' brushes' at tips when dry; capsule immersed; siliceous rocks in mountains; no nerve — Hedwigia ciliata

More densely tufted; shoots dull or dark grey-green; hair- points not uniting to form obvious terminal brushes; capsule on evident seta. Like Grimmia trichophylla but it has wider leaf and broader base to the hair-point — Rhacomitrium heterostichum

8 Stems very short (0.5-1 cm. tall) — 9

Stems taller — 10

9 Blackish plant of siliceous rocks on mountains. Like G. pulvinata but cushions not dense and mound-like — Grimmia doniana

Green plant very common on lowland walls, etc.; lots of capsules with spiral peristome teeth — Tortula muralis

10< Plant tinged, sometimes strongly, with reddish brown (at least on undersides of leaves) — 11

Plant some shade of green —12

11 Leaves large (3-5 mm.), with broad tips, widely spreading- recurved when moist; rarely fertile, but if so, seta present; leaf top narrows abruptly (in T. ruraliformis narrows gradually) — Tortula ruralis (= Barbula ruralis)

Leaves smaller (1.5 mm.), narrow at tips, never spreading- recurved; often very fertile; capsules immersed, with red lids (achterlichtmos<); glass hair toothed — Grimmia apocarpa (= Schistidium apocarpum)

12 Cushions dense, hemispherical, seta strongly recurved (when young and moist); very common on lowland wall tops — Grimmia pulvinata

Cushions looser, not mound-like or hemispherical as above; seta straight —13

13 Leaves with wide apices, spreading-recurved when moist; dense golden-green tufts or cushions on roofs or calcareous rocks — Tortula ruralis

Leaves with narrow apices, spreading-recurved when moist; on siliceous rocks — Rhacomitrium heterostichum

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