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Sphagnum Linnaeus, 1753

With nearly 200 species worldwide, Sphagnum covers large expanses especially in high latitudes, and it plays a dominant role in its ecosystem. Anyone working on bryophytes in temperate to polar regions should quickly become familiar with recognizing this genus. The features that should be emphasized in field recognition are the pale coloration, the fasciculate branching and the apical cluster of branches (capitulum). Among mosses, Sphagnum is the most economically utilized, and this is reflected in a number of guides to the species in the genus.

Key to Sphagnum

Species included in this key are in Sphagnaceae:
Sphagnum angustifolium (C. E. O. Jensen ex Russow) C. E. O. Jensen in Tolf, not known from CA
Sphagnum bartlettianum Warnstorf
Sphagnum capillifolium (Ehrhart) Hedwig
Sphagnum centrale C. E. O. Jensen, not known from CA
Sphagnum compactum Lamarck & A. P.de Candolle
Sphagnum contortum Schultz
Sphagnum fallax (Klinggräff) Klinggräff, not known from CA
Sphagnum fimbriatum Wilson in W. J. Hooker
Sphagnum fuscum (W. P. Schimper) Klinggräff
Sphagnum girgensohnii Russow
Sphagnum henryense Warnstorf
Sphagnum imbricatum Hornschuch ex Russow, not known from CA
Sphagnum inundatum Russow
Sphagnum lescurii Sullivant in A. Gray
Sphagnum magellanicum Bridel
Sphagnum mendocinum Sullivant
Sphagnum palustre Linnaeus
Sphagnum papillosum Lindberg
Sphagnum platyphyllum (Lindberg) Warnstorf
Sphagnum quinquefarium (Lindberg in Braithwaite) Warnstorf
Sphagnum recurvum Palisot de Beauvois, not known from CA
Sphagnum rubellum Wilson, not known from CA
Sphagnum russowii Warnstorf
Sphagnum squarrosum Crome in Hoppe
Sphagnum strictum Sullivant
Sphagnum subnitens Russow & Warnstorf
Sphagnum subsecundum Nees in Sturm
Sphagnum tenellum (Bridel) Bory, not known from CA
Sphagnum teres (W. P. Schimper) Ångström in C. J. Hartman
Sphagnum warnstorfii Russow

Sphagnum is so distinctive as to resemble no other moss in the state. It follows that species identification of Sphagnum requires a very different suite of preparations from that done with other mosses. One must distinguish between the upright stem axis and its leaves and the branch axes with their leaves. With the stem axis, it is necessary to have a surface view of that axis after removing leaves and branches. It is also necessary to take a cross-section of that axis to determine the number of layers of thin-walled cortical cells outside of the thick-walled medulla (the ‘wood' cylinder). The stem leaves usually differ radically in shape and cellular morphology from the branch leaves. One finds the stem leaves by removing all the branches and then carefully removing one of the stem leaves (usually radically broader than the branch leaves). With the branch leaves, it is necessary to take a cross-section. Cross-sections are made holding down entire leafy branch axes and chopping sections from the constituent leaves by razor blade cuts across the entire leafy axis. In addition to the required branch leaf cross-sections, we require branch leaf whole-mounts and branch stems denuded of leaves.

Many of the characters used in Sphagnum refer to pores whose digestion patterns are taxon specific. Similarly, larger portions of the cell walls of leaves, especially stem leaves, may be digested at maturity (resorbed). These pores and resorption areas, their size and arrangement, may be difficult to view without staining. Traditionally, crystal violet is used in such staining, but the blue colors in a child's water color set work just as well. Simply take the moist and leafy stem or branch to a slide and put a droplet of stain on it prior to dissection and viewing.

Sphagnum in California is restricted to perennially saturated soils in bogs and fens — waterlogged sites that depend upon up-welling of perennially cold water. The distribution of each species seems to be relictual in that each of the California species is strongly discontinuous in distribution. Sphagnum has never been found with sporophytes in California.

A. Cortical cells of stems and branches with spiral fibrils; apex of branch leaves concave and cucullate with abaxial surface appearing roughened by irregular digestion of the leucocyst walls .....B
A. Cortical cells of stem and branches without spiral fibrils; apex of branch leaves usually not cucullate .....G

B. Chlorocysts completely included within the layer of hyalocysts, or with slight and equal exposure of the lenticular chlorocysts on both surfaces .....C
B. Chlorocysts with a broad base of exposure on the adaxial surface, not exposed or only slightly exposed on the abaxial surface .....D

C. Plant typically with a reddish to copper blush .....Sphagnum magellanicum
C. Plant greenish to whitish green, never reddish tinged .....Sphagnum centrale not known from CA

D. Chlorocysts mostly almost as broad on the adaxial surface as they are deep, thus appearing in cross-sections equilateral-triangular; leucocysts of stem leaves, especially near the leaf base, appearing once divided by an oblique fibrillose thickening of the cell wall .....E
D. Chlorocysts on adaxial surface markedly more narrow than deep, thus appearing in cross-sections isosceles-triangular; leucocysts of stem leaves without oblique fibrillae .....F

E. Chlorocysts, especially near the branch leaf bases, with abundant comb-fibrils; innermost walls of innermost layer of stem cortical cells horizontally striate .....Sphagnum imbricatum
E. Chlorocysts papillose on walls shared with leucocysts; cortical cells without horizontal striae .....Sphagnum papillosum

F. Hyalocysts of the branches with rounded-elliptic pores on the abaxial surface; chlorocysts, especially near the leaf base showing extensive development of comb-fibrils (seen as minute papillose roughenings of the lateral walls of those chlorocysts) .....Sphagnum henryense
F. Hyalocysts of the branches with narrowly elliptic pores on the abaxial surface; chlorocysts without such comb-fibrils .....Sphagnum palustre

G. Cortical cells of branch stems isomorphic and distally porose (seen in branch cross-section as a single layer of uniform-sized enlarged outer cells); branch leaves truncate and denticulate at apex, much larger than the broadly deltoid stem leaves .....H
G. Cortical cells of branch stems dimorphic with only the larger ones porose (seen in branch cross-section as a layer of enlarged outer cells of two differing diameters); branch leaves usually narrowed and involute to an apex of varying shapes but not significantly truncate; branch leaves not much larger than the stem leaves .....I

H. Chlorocysts of branch leaves completely included; abaxial surface of hyalocysts of branch leaves with numerous pseudopores (ringed structures that resemble pores but lack digestion of actual holes) .....Sphagnum compactum
H. Chlorocysts of branch leaves with broadest exposure on the abaxial surface; hyalocysts of branch leaves without pseudopores .....Sphagnum strictum

I. Chlorocysts of branch leaves with broadest exposure on the adaxial surface (look at and visually compare the chlorocysts of both surfaces of the leaf whole-mount) .....J
I. Chlorocysts with broadest exposure on the abaxial surface, or with essentially equal or no exposure .....S

J. Stem leaves truncate or broadly rounded with distinct fimbriae across a distance equal to at least half the leaf width; central basal area of stem leaf with outer cell walls strongly resorbed forming a triangular, transparent and well demarcated central zone .....K
J. Stem leaves narrowed to apex, often notched but never fimbriate; central basal area of stem leaves without such a well demarcated central zone .....L

K. Stem leaves broadest near the apex, fringed across entire apex with the fringe often continuing even to the lateral margins .....Sphagnum fimbriatum
K. Stem leaves somewhat narrowed toward apex, fimbriate only in the central 1/2-3/4 of apex .....Sphagnum girgensohnii

L. Ascending branches mostly 3 per fascicle; stem leaves bordered below by elongate cells comprising over 1/2 of leaf base, bordered above nearly to apex by a margin of elongate cells 3 or more cells wide .....Sphagnum quinquefarium
L. Ascending branches mostly 2 per fascicle; stem leaves more narrowly bordered .....M

M. Plant, especially the inner cells of the stem, brown, never red; plant forming very compact clones in bogs of low mineral availability; cortical cells of stem without pores (view a number of cells on stems stained with crystal violet) .....Sphagnum fuscum
M. Plant with some reddish cast, or reddening when placed in dilute chlorox solution; clones rather loosely arranged; cortical cells of stem porose or not .....N

N. Stem leaves appearing acuminate to abruptly apiculate because of the strongly involute upper margins .....O
N. Stem leaves mostly with plane margins, or with margins not so much involute as to make the leaf apex appear narrowed .....Q

O. Leucocysts in median portions of branch leaves contacting the adjacent chlorocysts over only a small portion of their surface and thus hemispheric-convex on the abaxial surface; leaves of dry plant glossy .....Sphagnum subnitens
O. Leucocysts in median portions of branch leaves having a free convexity that describes less than 180 of arc; dry leaves not glossy .....P

P. Stem leaves more than 3:1; branch leaves noticeably 5-ranked; abaxial surface of proximal hyalocysts of stem leaves usually fibrillose throughout .....Sphagnum bartlettianum
P. Stem leaves less than 2.5:1; branch leaves not noticeably ranked; abaxial surface of proximal hyalocysts of stem leaves usually with membrane gaps .....Sphagnum capillifolium

Q. Hyaline cells in distal portion of branch leaves with ringed pores whose width is about 1/5 of width of the cell; cortical cells of stem without pores .....Sphagnum warnstorfii
Q. Hyaline cells in distal portion of branch leaves with larger pores (mostly about 1/3 of cell width) only obscurely ringed .....R

R. Cells of stem cortex mostly with pores; hyalocysts of stem leaves undivided, mostly short-rhomboidal .....Sphagnum russowii
R. Cells of stem cortex without pores; hyalocysts of stem leaves long rhomboidal, with cross-fibrils .....Sphagnum rubellum not known from CA

S. Stem leaves mostly broadly triangular with the apex truncate, erose to nearly entire at apex; pores on abaxial portion of leucocysts of branch leaves to about 1/5 of width of those leucocysts .....T
S. Stem leaves mostly ligulate, 3-4:1, quite lacerate at the apex; pores on abaxial portion of leucocysts of branch leaves mostly more than 1/3 as broad as the leucocyst .....U

T. Branch leaves abruptly contracted to the squarrose limb; leucocysts with ringed pores on adaxial surface .....Sphagnum squarrosum
T. Branch leaves gradually contracted with the limb not usually strongly squarrose; leucocysts not ringed or inconspicuously so .....Sphagnum teres

U. Clorocysts of branch leaves truncately elliptic with equal exposure on both surfaces; leucocysts of branch leaves with numerous small pores visible on the abaxial surface of the leaf, these pores strongly ringed and located at the junction of the spiral fibrils and the lateral cell margin; ascending and descending branches similar in length and degree of attenuation .....V
U. Chlorocysts of branch leaves triangular and exposed on dorsal surface; leucocysts mostly without so numerous commissural pores and often with those pores more centrally located over the lumen; descending branches significantly longer and more attenuate than the ascending ones .....Z

V. Stem cross-section showing 2-3 complete layers of enlarged and thin-walled cortical cells .....W
V. Stem cross-section showing a single layer of enlarged and thin-walled cortical cells .....X

W. Terminal bud protruding above capitulum and thus very obvious; stem leaves broadly elliptic, at least as large as branch leaves; ascending and descending branchlets of fascicle not clearly differentiated .....Sphagnum platyphyllum
W. Terminal bud inconspicuous within capitulum; stem leaves oblong to deltoid, smaller than branch leaves; ascending and descending branchlets of fascicle often somewhat differentiated .....Sphagnum contortum

X. Stem leaves mostly 1/3-1/2 as long as the branch leaves; hyalocysts of stem leaves mostly undivided .....Sphagnum subsecundum
X. Stem leaves mostly markedly more than 1/2 as long as the branch leaves; hyalocysts of stem leaves mostly with several cross-fibrils .....Y

Y. Abaxial face of hyalocysts of stem leaves with numerous pores but with such pores few on the adaxial face .....Sphagnum lescurii
Y. Abaxial face of hyalocysts of stem leaves with few pores but with such pores numerous on the adaxial face .....Sphagnum inundatum

Z. Stem and branch leaves similar in size and shape and in cellular detail .....Sphagnum tenellum
Z. Stem and branch leaves quite dissimilar .....AA

AA. Branch leaf hyalocysts with pores on abaxial surface arranged in close rows along the commissures .....Sphagnum mendocinum
AA. Branch leaf hyalocysts without such a close commissural arrangement .....AB

AB. Stem leaves trapezoidal, truncate at the broad and fimbriate to dentate apex .....Sphagnum recurvum
AB. Stem leaves deltoid-triangular, about as broad as long, terminating in an acute to bluntly acute apex .....AC

AC. Branch leaves, when dry, strongly undulate, spreading at apices; capitula large and 5-radiate; stem leaves 0.7-1.1 mm long .....Sphagnum fallax
AC. Branch leaves, when dry, appressed, hardly undulate; capitula small, not conspicuously 5-radiate; stem leaves 0.4-0.8 mm long .....Sphagnum angustifolium

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