Syntrichia Bridel, 1801.

Syntrichia princeps, cross-section of costa showing hydroids (semi-circle drawn out to a point) in the most central position between crescent-shaped stereid band and guide cells

Syntrichia is one of a group of Pottiaceous mosses usually characterized by pluripapillose cells and C-shaped papillae. Mosses included in the genus Syntrichia have been viewed as part of the larger genus Tortula. Both generally have ligulate leaves. Plants of Syntrichia are generally larger than those of Tortula, but distinctions are made on the basis of costa cross-section morphology. Both genera have only an abaxial stereid band but that band is elliptic in Tortula whereas it is crescentic in Syntrichia. The abaxial face of the costa has an epidermis in Tortula – a feature lacking in Syntrichia.

Key to Syntrichia Etc.

Species included in this key are in Pottiaceae, except Encalypta (Encalyptaceae):
Encalypta rhaptocarpa Schwägrichen
Syntrichia amplexa (Lesquereux) Zander
Syntrichia bartramii (W. C. Steere in Grout) Zander
Syntrichia bolanderi (Lesquereux & T. P. James) Zander
Syntrichia caninervis Mitten
Syntrichia laevipila Bridel
Syntrichia latifolia (Bruch ex C. J. Hartman) Hübener.
Syntrichia montana Nees, recognized from CA since 2004
Syntrichia norvegica Weber
Syntrichia obtusissima (C. Müller Hal.) Zander
Syntrichia pagorum (Milde) Amann
Syntrichia papillosa (Wilson in Spruce) Juratzka
Syntrichia papillosissima (Coppey) Loeske
Syntrichia princeps (De Notaris) Mitten
Syntrichia ruralis (Hedwig) Weber & D. Mohr
Syntrichia sucrosa K. M. Kellman, recognized from CA since 2004
Syntrichia virescens Boros, recognized from CA since 2004
Tortula inermis Bridel

Work with Syntrichia requires a stem cross-section preferably made within a few millimeters of the stem apex. It also requires a cross-section of a leaf made near mid-leaf. The central strand in the stem cross-section is a group of smaller cells, mostly with thick walls, abruptly differentiated from the large and thin walled cells of the stem medulla. Harder to see are the hydroids of the costa cross-section. These are partially crushed cells (or even a single cell) immediately abaxial to the guide cells and centrally placed.

Syntrichia is a genus specially adapted to our mediterranean climate, but poorly represented in climates with a summer maximum of precipitation. Examples of this genus grow in all parts of state, on rocks, tree trunks and soil. Often several species grow seemingly intermixed in even a small area.

A. Hyaline awn consistently absent; sometimes mucronate to apiculate or with a few enlarged apical cells .....B
A. Hyaline awn present on at least some leaves .....E

B. Leaf cells smooth to mammillose, or with a few small papillae in distal portion of leaf; cells of basal leaf margin markedly more narrow and thicker walled than adjacent rectangular basal cells; cells of upper leaf margin somewhat smaller and more pellucid than interior cells .....Syntrichia amplexa
B. Leaf cells papillose, usually densely so; margin various .....C

C. Leaves spatulate to oblong-obovate, broadest in distal region; spherical, multicellular gemmae produced on leaf lamina; plant corticolous on streamside trees .....Syntrichia latifolia
C. Leaves broadest at or below the middle; gemmae absent or placed on the rhizoids .....D

D. Leaf, above the basal area of rectangular cells, bordered with several rows of smaller, less papillose cells .....Syntrichia bolanderi
D. Leaves not so bordered .....Tortula: T. inermis

E. Leaf lamina bistratose above; plant very dark blackish, of desert soils .....Syntrichia caninervis
E. Leaf lamina bistratose only at margins or in apex, if at all .....F

F. Margin plane to ascending, or sometimes with inconspicuous recurvature near or below the leaf middle .....G
F. Margin recurved, often strongly so (though weakly in S. laevipila); gemmae mostly absent; habitat various .....J

G. Median leaf cells unipapillose on abaxial surface, smooth or nearly so on adaxial surface; plants with conspicuous gemmae on leaf, mostly epiphytic especially in riverine corridors .....Syntrichia papillosa
G. Median leaf cells pluripapillose on both surfaces; gemmae absent or restricted to leaf axils .....H

H. Plant bearing multistratose, leaf-like gemmae in axillary clusters at stem apex; costa smooth on abaxial surface; plant mostly epiphytic, almost restricted to cultivated areas .....Syntrichia pagorum
H. Plant without gemmae; costa papillose on abaxial surface; plant epilithic in dry scrub or in desert areas .....I

I. Cells of basal portion of leaf rectangular and abruptly inflated; costa not or almost imperceptibly tapered; sporophytes unknown in the species ..... Syntrichia bartramii
I. Cells of basal portion of leaf rectangular and somewhat incrassate, only gradually demarcated from the isodiametric median cells; costa tapered from a broad base to a very narrow apex; calyptra campanulate and sheathing the entire capsule .....Encalypta: E. rhaptocarpa

J. Costa showing hydroids in cross-section (this appears as a gap that comes to a sharp point between two guide cells, though it really consists of several cells); stem cross-section with central strand (cells in the center are smaller, angular and often crushed); median juxtacostal cells more than 15 µm in diameter; plant mostly monoicous .....K
J. Costa without hydroids; stem without central strand; median juxtacostal cells mostly about 12 µm; plant dioicous .....P

K. Margins recurved weakly about midleaf; costa tends toward a yellowish-brown when viewed with transmitted light; awn mostly smooth to remotely toothed, often rather flexuose; leaves mostly somewhat spatulate, less than 3 mm long; internal cells of lamina at juncture with basal cells not collenchymatous ..... Syntrichia laevipila
K. Margins more strongly recurved; costa tends toward reddish-brown; awn closely covered with teeth, often reddish-brown near base, in most species somewhat rigid; leaf shape and size various; internal cells of lamina at juncture with basal cells sometimes collenchymatous .....L

L. Plant large (seta 20 mm; stem generally quite long and cloaked with leaves); mid-laminal cells toward costa 12-17 µm; apex broadly rounded, with the lamina not retuse where it attaches to awn; distal portion of costa spinose to prorate abaxially; synoicous (sporophytes numerous and no perigonia is a suggestive field character) .....Syntrichia princeps
L. Plants not unusually large (seta <<20 mm; stems in most cases shorter); mid-laminal cells smaller or larger; leaves (or many of them) retuse at apex .....M

M. Cells 8-12 µm in diameter .....N
M. Cells generally larger .....O

N. Papillae merely bumps on the cells, which are not mammalose; not appearing frosted ..... Syntrichia montana
N. Papillae pedicellate on more or less mammalose cells; as seen in hand often with a 'sugary' frosting .....Syntrichia sucrosa

O. Lamina inrolled but immediate margin recurved (giving the distal third of leave a concave appearance); green part of leaf about twice as long as wide with widest point more than half way from start of green part to tip; abaxial side of cells often pigmented orangish (like the costa but not so much) ..... Syntrichia speciesA
O. costa yellowish to brownish, smooth throughout (not very prorate) except on the hyaline awn .....Syntrichia obtusissima

P. Awn weak and somewhat flexuose, often reddish-brown except at its extreme apex; costa in distal 1/4 of leaf with substereids replacing the stereid cells of the stereid bands [the cells abaxial to the guide cells sometimes almost as large as the guide cells and thinner walled than the stereids]; margin plane in distal 1/4; plant of moist rocks at high elevations .....Syntrichia norvegica
P. Awn hyaline throughout, sometimes somewhat reddish brown at its insertion on the leaf lamina; costa with abaxial stereid bands with stereid cells very thick-walled and with lumen appearing as mere pin-pricks [the cells abaxial to the guid cells, even if thiner walled than most stereids, not much larger in diameter when including the wall than the stereids; margin recurved nearly to apex; habitat various .....Q

Q. Leaf in cross-section showing high, branched papillae that interlock so as to give a grossly tristratose appearance; plant of eastern deserts and scrublands .....Syntrichia papillosissima
Q. Papillae not so high and interlocking; plant habitat various .....Syntrichia ruralis