Schistidium Bruch & W. P. Schimper in Bruch & W. P. Schimper, 1845.

Schistidium has frequently been considered to be merely an infrageneric category within Grimmia. We have discussed distinction of the two genera in the section on Grimmia. Species of Schistidium tend to occupy different ecological sites from those of Grimmia. Schistidium is most common on rock outcrops in areas of occasional submergence. It is especially common in sheet drainage areas over rock outcrops. Most often Schistidium can be found with capsules if one looks carefully in the field. The glossy red urns of the sporophytes of most Schistidium are quite obvious when one looks at moist plants. Species that sparingly produce sporophytes will often have those sporophytes on plants on the downhill edge of the clone. Sterile material thought to be Schistidium might profitable be keyed both in the Schistidium and in the Grimmia keys. Recent work by Hans Blom has been invaluable in our understanding of Schistidium. Monographic study of California Schistidium would be a worthwhile enterprise.

Key to Schistidium Etc.

Mosses treated in this section are blackish acrocarps usually with a reddish blush. The lanceolate to ovate-lanceolate leaves may or may not have an hyaline awn. Most species have a rather large number of quadrate cells in the alar region, and they often lack the transverse wall thickening of the basal marginal cells – a feature of many species of Grimmia as well. The definitive feature is the immersed and systylious capsules – the latter feature is never present in Grimmia.

Species included are all in Grimmiaceae:
Schistidium agassizii Sullivant & Lesquereux in Sullivant
Schistidium atrichum (C. Müller Hal. & Kindberg) W. A. Weber
Schistidium cinclidodonteum (C. Müller Hal. in Röll) Bremer
Schistidium confertum (Funck) Bruch & W. P. Schimper
Schistidium dupretii (Thériot) W. A. Weber
Schistidium flaccidum (De Notaris) Ochyra
Schistidium maritimum (Turner ex Scott) Bruch & W. P. Schimper
Schistidium occidentale (E. Lawton) Churchill in Funk & D. R. Brooks
Schistidium platyphyllum (Mitten) Persson in Persson & Gjaerev
Schistidium rivulare (Bridel) Podpera
Schistidium strictum (Turner) Loeske, not known from CA
Schistidium tenerum (J. E. Zetterstedt) E. Nyholm

A. Leaves muticous .....B
A. At least the perichaetial leaves with hyaline awns; median laminal cells extending along the margin nearly to the leaf base .....I

B. Leaves at least in the lower portion of the stem typically more than 4:1 .....C
B. Leaves typically broader .....F

C. Plants occasionally washed by salt spray of the ocean; not adaxially grooved or with sinuose rectangular cells on adaxial surface; costa cross-section exhibiting a strong abaxial stereid band .....Schistidium maritimum
C. Plants found away from immediate maritime rocks; costa cross-section without stereid bands .....D

D. Leaves almost consistently bi- to tri-stratose above the middle; costa flattened at the base and merging imperceptibly into the bistratose juxtacostal basal lamina .....Schistidium cinclidodonteum
D. Leaves mostly unistratose throughout or sometimes bistratose at extreme apex; costa at base terete and well set-off from adjacent lamina .....E

F. Upper leaf margin typically denticulate; plant usually submerged on riverside rocks .....Schistidium rivulare
F. Upper leaf margin entire; plant seldom submerged .....G

G. Leaves less than l mm long, not recurved or only minutely so at the base; cells 4-8 µm broad .....Schistidium atrichum
G. Leaves on well developed stems mostly over l mm long; margins recurved to near the middle; cells 7-10 µm broad .....H

H. Urn ovoid, not much broadened to the apex; leaves to 1.5 mm long .....Schistidium dupretii
H. Urn broad at the mouth, gradually narrowed to the base; leaves mostly more than 2 mm long .....Schistidium platyphyllum

I. Leaf margins plane to incurved; leaves mostly long-lanceolate, more than 6:1; awn very minute, mostly less than 5 cells in length, smooth .....Schistidium cinclidodonteum
I. Leaf margins recurved, at least on one side near base .....J

J. Leafy stems less than 0.5 mm wide and mostly less than 25 mm long; leaves less than l mm long; plants forming wiry chestnut-brown turfs on seepages at high elevations .....Schistidium tenerum
J. Plants and leaves larger .....K

K. Leaves with at least a few papillae on dorsal surface, often rather densely covered; urn broadened toward the mouth; peristome spreading from mouth of urn .....Schistidium strictum not known from CA
K. Leaves smooth throughout; urn evenly ovoid; peristome erect or absent .....L

L. Peristome absent or present as irregularly truncate segments .....Schistidium flaccidum
L. Peristome present and well developed .....M

M. Vegetative leaves mostly more than 1.5 mm long with the perichaetial leaves exceeding 3 mm long; peristome teeth deep red, not or very little cribrose; transverse walls of basal marginal cells not thickened ..... Schistidium species A
M. Vegetative leaves and perichaetial leaves smaller; peristome teeth pale- or bleached red-brown, strongly cribrose; transverse walls of basal marginal cells markedly thicker than the lateral walls .....N

N. Leaves frequently with a hyaline awn and with that awn terete and serrate on its entire circumference; plant when moist with leaves spreading, often almost squarrose ..... Schistidium species B
N. Hyaline awn mostly found on some of the perichaetial leaves, only occasionally on vegetative leaves; plant when moist with leaves ascending to erect-ascending .....Schistidium confertum