Fissidens Hedwig, 1801

Fissidens sublimbatus Coleman 1307

Fissidens is one of the easiest mosses to identify to genus, but with perhaps 600 species worldwide, specimens may be exceptionally difficult to identify to species. We are indebted to Dr. Ronald Pursell for our understanding of the genus Fissidens (most recently Pursell 2007). All species of Fissidens have "equitant leaves," a feature involving an apparent splitting of the basal region so that the two sides of the split clasp the stem in the manner of the base of an Iris leaf. The clasping base is the "vaginant lamina." Distal to the vaginant lamina is the "distal lamina," and, derived from a single abaxial ridge on the costa is the "dorsal lamina." Fissidens varies in size from some of the smallest of our more or less acrocarpous mosses to some that may even reach 15 mm high. Our species of Fissidens include large plants of flooded rocks, often in rapidly flowing streams as well as on wet rock walls of streams and seeps, and our smaller species grow primarily on disturbed soil.

Key to Fissidens Etc.

Included in the key that appears below are all the local mosses with the leaves inserted in two ranks. This is in contrast to "complanate mosses" – plants that appear flattened despite a spiral insertion of the leaves. Carefully observe the leaves at their lines of insertion on the stems. All complanate mosses have leaves inserted on the dorsal portion of the flattened stem and only subsequently twisted into the dominant plane. Mosses keyed here are inserted along two ranks.

Species included in this key are in Fissidentaceae, except Bryoxiphium (Bryoxiphiaceae), Distichium (Ditrichaceae), and Schistostega (Schistostegaceae):
Bryoxiphium norvegicum (Bridel) Mitten, not known from CA
Distichium capillaceum (Hedwig) Bruch & W. P. Schimper
Distichium inclinatum (Hedwig) Bruch & W. P. Schimper
Fissidens adianthoides Hedwig
Fissidens aphelotaxifolius Pursell
Fissidens asplenioides Hedwig, not known from CA
Fissidens bryoides Hedwig
Fissidens crispus Montagne
Fissidens curvatus Hornschuch
Fissidens dubius Palisot de Beauvois
Fissidens fontanus (Bachelot de la Pylaie) Steudel
Fissidens grandifrons Bridel
Fissidens minutulus Sullivant
Fissidens obtusifolius Wilson, recognized from CA since 2004
Fissidens osmundioides Hedwig, not known from CA
Fissidens pauperculus M. A. Howe
Fissidens sublimbatus Grout
Fissidens taxifolius Hedwig
Fissidens taylorii C. Müller Hal.
Fissidens ventricosus Lesquereux
Schistostega pennata (Hedwig) Weber & D. Mohr, not known from CA

A. Leaves ampliate clasping with the antical base carinate and pocketing the stem allowing the definition of a "vaginant lamina" differentiated from the more distal, non-carinate "apical lamina" and the costal ridge which serves as a "dorsal lamina" .....B
A. Leaves deeply carinate but without differentiation into a dorsal and an apical lamina thus the plant not identifiable to Fissidens .....Q

B. Leaves with a strong border of elongate cells on all laminae .....C
B. Leaves not bordered, or bordered on vaginant laminae or with a group of lighter cells on dorsal and apical laminae .....H

C. Plant of submerged rocks in flowing streams; leaves more than 2 mm long; lamina and margin with bistratose streaks .....Fissidens ventricosus
C. Plant usually on soil; leaves smaller; lamina consistently unistratose .....D

D. Leaves narrowly attenuate with the dorsal lamina ending above the leaf base; laminal cells 2-4:1; sterile plants consistently larger and with more clearly distichous leaves than the archegoniate ones .....Fissidens curvatus
D. Leaves not strongly attenuate; dorsal lamina extending to or near the leaf base; laminal cells nearly isodiametric; sterile and archegoniate plants not strongly differentiated .....E

E. Cells of the lamina about as broad as thick in cross-section, mostly not very bulging; dorsal lamina extending downward and inserted on the stem; plants of rather moist habitats .....Fissidens bryoides
E. Cells of the lamina markedly broader than thick in cross-section, mostly bulging mammillose; dorsal lamina mostly not extending downward to leaf insertion; plants of moist or dry habitats .....F

F. Dorsal lamina tapering to extinction at leaf insertion; plant of soils in dry grasslands .....Fissidens sublimbatus
F. Dorsal lamina continuing to leaf insertion; plant of moist sites mostly in western California .....G

G. Limbidium ending more than two cells below leaf apex; base of stem strongly reddened; plant usually on rocks .....Fissidens minutulus
G. Limbidium confluent with costa at apex; base of stem not reddened; plant usually on soil .....Fissidens crispus

H. Leaves with a rigid, multistratose lamina, 3-5 mm long; plant aquatic to semiaquatic especially in calcareous regions .....Fissidens grandifrons
H. Lamina unistratose and smaller .....I

I. Leaves flaccid, blackening when dry, mostly more than ten times as long as wide, with the vaginant lamina less than 1/3 leaf length; plant immersed or seasonally immersed in streams and ponds, often calcareous .....Fissidens fontanus
I. Leaves neither flaccid nor so long; plant not aquatic .....J

J. Leaves serrate in distal one-half .....K
J. Leaves crenulate to entire .....L

K. Median leaf cells to 12 µm in longest dimension; leaf lamina unistratose throughout .....Fissidens adianthoides
K. Median leaf cells smaller; lamina at mid and upper leaf with bistratose streaks .....Fissidens dubius

L. Vaginant lamina with a somewhat defined limbidium; dorsal and apical laminae with markedly smaller cells on margin even to near the apex; costa percurrent; fertile plants markedly smaller than sterile plants .....Fissidens taylorii
L. Vaginant lamina elimbate; dorsal and apical laminae mostly not bordered or with marginal cells both smaller and paler than immediate interior cells; costa various; fertile and sterile plants of similar size and development .....M

M. Costa excurrent to percurrent on at least some of the leaves of the plant .....N
M. Costa ending below the leaf apex .....O

N. Median leaf cells smooth to slightly bulging, almost pellucid in dorsal microscopic view; leafy plants mostly less than 2 cm long; leaf apex excluding apiculus acute .....Fissidens aphelotaxifolius
N. Median leaf cells strongly mammillose-bulging, opaque in dorsal microscopic view; leafy plants mostly more than 2.5 cm long; leaf apex excluding apiculus obtuse to rounded .....Fissidens taxifolius

O. Plant less than 5 mm tall; marginal cells of leaf smaller and paler than immediate interior cells .....Fissidens pauperculus
O. Plant mostly more than 10 mm tall; marginal cells not so differentiated .....P

P. Median leaf cells less than 10 µm in longest dimension; leaves crenulate throughout .....Fissidens asplenioides not known from CA
P. Median leaf cells more than 12 µm in longest dimension; leaves with at least a few serrulations near apex but crenulate below .....Fissidens osmundioides not known from CA

Q. Leaf without any keeling, arranged flat in vertical rows; leaves confluent with one another by means of a decurrent postical base that is continuous with the antical base of the next leaf below thus resembling the leaflet arrangement of the fern Osmunda .....Schistostega: S. pennata not known from CA
Q. Leaves base carinate and pocketing the stem; leaves not confluent with one another on the stem .....R

R. At least the proximal portion of the stem with bluntly rounded leaves, without a subula; distal portion of fertile stems with long but erect subulae .....Bryoxiphium: B. norvegicum not known from CA
R. All the fully developed leaves with a defined, glossy base and with a divergent subulate apex .....S

S. Plant evenly and uniformly distichous; capsule erect and symmetric; spores 17-20 µm; plant paroicous .....Distichium: D. capillaceum
S. Plant obviously distichous but with some portions of that plant rather obscurely so; capsule inclined and asymmetric; spores 30-40 µm; plant autoicous .....Distichium: D. inclinatum