Taxon	Illustrator ⠉
	Ctenidium molluscum	Patricia M. Eckel
	Ctenidium schofieldii	Patricia M. Eckel

Plants small to medium-sized, seldom large, in loose mats, light green, dull. Stems usually creeping, pinnate or subpinnate; hyalodermis absent, central strand present; pseudoparaphyllia triangular to ovatelanceolate. Stem and branch leaves differentiated. Stem-leaves spreading, falcate, ovatelanceolate to triangular-acuminate, not or weakly plicate; base broadly decurrent; margins usually recurved basally, plane distally, denticulate; apex acuminate from near base or mid leaf; costa usually double, short or to 1/4 leaf length; alar cells weakly differentiated, short to long-rectangular; laminal cells distally prorulose abaxially. Branch leaves longer lanceolate, smaller. Specialized asexual reproduction absent. Sexual condition dioicous; outer perichaetial leaves weakly reflexed, inner leaves erect, ovatelanceolate, apex acuminate. Seta reddish, smooth, occasionally scabrous near capsule. Capsule nodding to horizontal, short-elliptic to cylindric and curved, not or somewhat constricted below mouth; annulus somewhat differentiated, 1-seriate or 2-seriate, cells large; operculum conic-apiculate; peristome double; exostome teeth with external surface with zigzag central line, lamellose, striolate proximally, papillose distally; endostome basal membrane high, segments as high as exostome, keeled, cilia 1–3, elongate. Calyptra weakly prorulose distally, hairy. Spores spheric, finely papillose.

Distribution

Nearly worldwide (with concentration in se Asia), temperate and tropical areas

Discussion

Species ca. 21 (2 in the flora).

The recent revision by N. Nishimura (1985) provides a standard reference for this large genus of difficult to distinguish species. At the genus level, Ctenidium is quickly identified by the combination of the absent stem hyalodermis, laminal cells prorulose abaxially at distal ends, and falcate leaves. Ctenidium differs from Hypnum and most other genera of Hypnaceae by the prorulose laminal cells; it differs from the prorulose Chryso-hypnum by the prorulae evident at both cell ends, not just the distal ends, and leaves approximately straight, not curved. The axillary hairs are 3-celled; the leaf bases are often cordate and often concave between the alar region and costa; the basal laminal cells are short-rectangular, and the medial cells are long-rectangular. The antheridiate plants are usually smaller than the archegoniate; the exostome teeth are subulate-acuminate, yellow-brown, and internally trabeculate; and the endostome segments are pale yellow, weakly papillose, and split along the median line.

Selected References

None.

Lower Taxa

Ctenidium molluscum, Ctenidium schofieldii

Key

1	Leaves at stem apices unevenly divergent; stem leaf apices acuminate from mid leaf; stem leaf laminal cells 50-80 µm, weakly prorulose; margins weakly denticulate; branch leaf margins recurved basally.	Ctenidium schofieldii
1	Leaves at stem apices evenly divergent; stem leaf apices acuminate from near base; stem leaf laminal cells 40-50 µm, strongly prorulose at least distally; margins strongly denticulate; branch leaf margins rarely recurved basally.	Ctenidium molluscum