Species description:
Genus name denoting a torn cap, in reference to the lacerate fringe at the base of the calyptra of many species. Species name refer­ring to the pin-like beak of the operculum.

Reproduction:
Sporophytes frequent, dark brown to nearly black when ripe, maturing in spring.

Distinguishing characteristics:
The habitat on irrigated rock surfaces com­bined with the blunt-tipped leaves that have distant blunt teeth on the margins, plus the black erect sporangia on a long seta (when mature and old) usually separate this species.

Habit:
Dark green (sometimes almost black) to reddish-brown to orange-brown loose turfs to tufts, 20-50 mm tall, with leaves strongly divergent when wet and imbricate when dry; firmly affixed by dark brown to black rhizoids at the stem base.

Similar Species:
Schistidium rivulare and Orthotrichum rivulare grow in the same habitat and superficially resemble R. aciculave but their sporangia have an inconspicuous seta. R. aquaticum usually has yellow-­green plants and the leaf apex is strongly tapered to a bluntish point and shows no blunt marginal teeth on the leaves. Scouleria aquatica, also· of similar habitats, has sporophytes with very short setae and sporangia are sub spherical rather than cylindric. The leaves of Scouleria are strongly divergent when wet; those of R. aciculare are slightly diver­gent. R. pacificum is a smaller species of open outcrops near the coast; it has narrow tapering leaves that are rather blunt-tipped but lack widely spaced marginal teeth and the peristome teeth radiate outward when dry; in R. aciculare they are erect.

If more than one illustration is available for a species (e.g., separate illustrations were provided for two subspecies) then links to the separate images will be provided below. Note that individual subspecies or varietal illustrations are not always available.

Illustration Source:  Some Common Mosses of BC

Synonyms and Alternate Names:
Rhacomitrium aciculare (Hedw.) Brid.