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BFNA Title: Bryaceae, Key to Genera |
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The Bryaceae of the Bryophyte Flora of North America
Region John R. Spence National Park Service, Glen Canyon National Recreation Area, Page, AZ, 86040, U.S.A. Phone: (928) 608-6267; FAX: (928) 608-6283; email: John_Spence@nps.gov This treatment
has been posted in part to encourage other bryologists to examine members of
the Bryaceae and to test the proposed classification of North American
species presented below. Below, a key
to my generic concepts for the Bryaceae of North America north of Mexico is
presented. Roellia is included because it is very similar to Rhodobryum, and two species of Mielichhoferia that are closely
related and that are probably within the Bryoideae are also included. Leptobryum,
Epipterygium, Mielichhoferia type, Pohlia,
and Orthodontium are excluded. The key to
understanding Bryum is to be able
to determine the section a specimen of interest belongs to. Once the identity of the specimen is
narrowed down to a section of closely related species, then identification
becomes much easier. Principal
characters of the gametophore used in sectional assignment include stem
appearance (julaceous, comose, rosulate), leaf shape and condition when dry
(twisted, contorted, imbricate), leaf border, laminal cell shape, and the
presence of specialized gemmae.
Capsules are important in some sections, but can actually be a
hindrance in others because the presence of sporophytes appears to prevent or
at least reduce the production of specialized gemmae. Capsule shape, orientation,
and peristome structure and development are important characters for
assigning a specimen to a section. Bryum and its relatives produce a remarkable array of
specialized vegetation reproductive structures (gemmae). I recognize six principal types, defined
below. In general, most species
produce either one or two of these structures, although many species lack
them altogether. Certain combinations
apparently don’t occur naturally. For example, only one leaf axis gemmae
type is produced per species. 1.
Rhizoidal tubers: these
are small sphaerical to pyramidal structures developed on rhizoids. Typical size is from about 60 µm to 500 µm
across. Important characters include
color, size, size of surface tuber cells, and whether the cells are smooth or
variously bulging or papillose. In
some species the tubers are produced on micronemata on the stem rather than
on rhizoids in the substrate. Similar
tubers occur in Pohlia. 2.
Leaf axis bulbils:
small structures resembling shoots with leaf primordia generally
present. These structures occur in
the leaf axils of sterile stems, do not form an obvious stalk attaching them
to the stem, and are easily dislodged.
Important characters are the size, development and shape of leaf
primordia, and number of bulbils per leaf axis. Similar bulbils occur in Pohlia and Mielichhoferia. 3.
Leaf axis filiform gemmae:
these are slender structures resembling rhizoids, but with numerous short
regularly shaped cells with straight cross walls. They can be branched or unbranched. Occasionally, filiform gemmae can be produced directly from
cells of the leaf. Filiform gemmae
are produced by species of Rosulabryum and Bryum. 4.
Stem tubers: swollen
potato-like structures at the base of stems on or in the substratum. These structures have only recently been
described, and to date have only been found in a few species in Bryum
section Doliolidium and Brachymenium section Dicranobryum,
all restricted to tropical or subtropical seasonally dry regions. 5.
Flagelliform branches:
these are slender innovations arising in masses from the axils of upper
leaves. Typically, they have leaf
buds or partly formed leaves (scale leaves), but tend to lack fully developed
leaves. They have been found in
species of Bryum and Rosulabryum. 6.
Filiform rhizoidal gemmae:
small filiform gemmae budding off rhizoids have been reported from Anomobryum
lusitanicum (I. Hag. ex Luis.) Thér., Bryum demaretianum Arts, and
B. tenuisetum Limpr. Their
occurrence elsewhere in the Bryaceae is not known. They are superficially remarkably similar to those found in
some species of Archidium. In addition to
gemmae, lamina areolation provides many important characters for
identification. Although all species of the Bryaceae have distal and median
lamina cells that are elongate, the ratio of length to width is important,
and also the similarity between these cells and the proximal (basal) cells
provide important identification clues.
I have recognized four principal patterns of laminal areolation that
appear to be correlated with phylogeny, i.e., species in a genus or
section tend to have the same type of areolation pattern. However, these should be considered
general tendencies, as there is some variation between closely related
species, different collections within species, and even leaves of different
age on the same plant. Three leaf
location terms and their correlation with the leaf are: distal (upper 1/3),
median (middle 1/3) and proximal (lower 1/3). 1. Anomobryum-type: heterogenous, distal and median lamina cells elongate,
mostly 4:1 or greater, long-rhomboidal, hexagonal or linear, proximal cells
wider and shorter than cells above, quadrate or short-rectangular, transition
often abrupt, giving the areolation a heterogeneous appearance. 2. Plagiobryum-type: homogeneous, all cells except in the alar region
elongate, mostly 4-8:1, no strong distinction between upper 2/3 and lower 1/3
of leaf. One species, Bryum
incrassatolimbatum Card., has Plagiobryum-like areolation except
the cells are relatively short and broad.
A few Pohlia species in
section Mniobryum (e.g., P.
wahlenbergii) show this pattern as well.
Similar areolation is found in Haplodontium and Bryum
apiculatum Schwaegr. 3. Rhodobryum-type: heterogeneous, distal and median lamina cells short
rhomboidal to hexagonal, 2-4:1, proximal cells the same width or narrower,
and the same length or longer, more regularly rectangular with squared-off
ends, transition rather gradual, but still giving the areolation a
heterogeneous appearance. Some
species, such as B. pallens or B. weigelii, have extremely long and
narrow rectangular proximal cells, while others, including B. caespiticium and B. pseudotriquetrum have cells that
tend to be the same length as the cells above and either the same width or
occasionally somewhat wider. 4. Pohlia-type: homogeneous, all lamina cells except those at leaf base
long and narrow, mostly linear or hexagonal, often thick-walled. In addition to the specific gemmae and areolation types, there are also four different costa cross-sectional types in the family. The cross-section descriptions are based on sections taken somewhere in the middle third of leaf, but not at the leaf base or tip. These types are named for a genus they are most characteristic of. 1. Anomobryum-type: costa lacking guide cells; one stereid band. 2. Bryum-type: costa with a single layer of guide cells abaxial to the
stereid band; one stereid band. 3. Rhodobryum-type: costa with two or more layers of
guide cells abaxial to the stereid band; one stereid band, strongly reduced
or usually absent. 4. Mnium-type: costa with one layer of guide cells between two stereid
bands (not in Bryaceae sensu Buck
and Goffinet) Size can be of
some use in identifying species of Bryum. Both stem length and leaf length
categories are described below. I
have adopted the leaf lengths from Ochi (1972). Stem
length: short (<10
mm), medium (10-30 mm), long (>30 mm). Leaf length: small (<1.5 mm), medium (1.5-3.0 mm), large (3.0-4.0 mm), robust (>4.0 mm). Key to Genera 1. Stems short, julaceous; leaves small, green, yellow-green to silver, if stems not julaceous then plants silver and proximal lamina cells quadrate; lamina areolation Anomobryum-type, costa Anomobryum-type ………………………..…… Anomobryum and Bryum type section 1. Plants and leaves of
various sizes; fertile stems not julaceous although innovations sometimes so; if plants silver then
proximal lamina cells elongate-rectangular, if julaceous then leaves >2 mm long and with red
tints; lamina areolation and costa type various …………….……………. 2 2.
Plants in dense rhizomatous cushions; leaves mostly imbricate with long
spinose partly hyaline hairpoint, lamina areolation dense, Anomobryum-type;
costa Bryum-type; capsules erect; epiphytic-corticolous or saxicolous,
peristome reduced, cilia absent ……………….…Leptostomopsis
(Brachymenium) systylium 2.
Plants not in dense rhizomatous cushions; areolation dense to lax, hairpoint
variable, typically not spinose, rarely hyaline, often absent, proximal
lamina cells short or long; costa type various; capsule erect to nodding,
peristome perfect or reduced; habitats various ……………….... 3 3.
Inflorescences appearing lateral; leaves soft with costa not reaching apex to
percurrent, rarely weakly excurrent, lamina areolation Plagiobryum-type, alar cells somewhat differentiated from
justacostal cells, quadrate; costa Anomobryum-type;
capsule shortly pyriform, lacking peristome or with exostome only …………….. Haplodontium (=Mielichhoferia
macrocarpa and M. tehamensis) 3.
Inflorescences terminal; leaves and costa various, percurrent to excurrent,
lamina areolation various, alar cells rarely differentiated from justacostal
cells, if so then capsule with double peristome; costa type various; capsule
shape various, peristome double …..……………….. 4 4.
Leaves strongly twisted, areolation Anomobryum-type,
apex broadly obtuse, costa extending into short stout point, Bryum-type, margins serrate above;
capsules erect; saxicolous or epiphytic-corticolous …………….... Brachymenium
macrocarpum 4.
Leaves variously twisted or contorted to imbricate, leaf apex acuminate to
acute, if obtuse then costa percurrent; costa variable, percurrent to long
excurrent, upper margins smooth to serrate, areolation-type various, costa
type various ; capsules nodding or erect, terricolous, saxicolous or
sometimes rotten wood but not epiphytic …………….. 5 5.
Lamina areolation Anomobryum-type,
or if Plagiobryum-type plants with abundant rhizoidal tubers; leaves
mostly imbricate or rarely slightly twisted at stem apex; stems either
budlike or elongate and evenly foliate; rhizoidal tubers and leaf axis
bulbils often present; costa Bryum-type ……………………... Bryum (Bryum sect. Apalodictyon, Alpiniformia,
Doliolidum, and Brachymenium sect. Dicranobryum) 5.
Lamina areolation either Rhodobryum-type
or Plagiobryum-type (and plants
lacking gemmae), leaves variously contorted, twisted or imbricate; stems
comose, rosulate or elongate and evenly foliate; rhizoidal tubers or leaf
axis filiform gemmae sometimes present; costa type various ……………………………….... 6 6.
Plants red-green to pink-silver, with soft imbricate leaves, innovations
sometimes julaceous, lamina areolation Plagiobryum-type,
limbidium lacking, costa Anomobryum-type; capsule distinctly
zygomorphic, endostome longer than exostome, seta distinctly curved …………….. Plagiobryum 6.
Plants lacking silvery tones, with variously shrunken, contorted or twisted
leaves, innovations not julaceous, lamina areolation Rhodobryum-type, leaf border of thick elongate cells usually
present, costa Bryum or Rhodobryum-type; capsules not
distinctly zygomorphic, peristome various, but exostome teeth longer than
endostome, seta straight …………………. 7 7.
Plants dull red or pink, stems long and evenly foliate, distal lamina cells
very short (1-3:1), broad, with many irregularly rhomboidal to subquadrate
cells; limbidium strong, bi- to multistraose; capsule suberect, somewhat
zygomorphic, spores small (10-15 µm) …………………... Bryum incrassatolimbatum 7.
Plants various colors and sizes, stems comose, evenly foliate or rosulate,
distal lamina cells mostly 3:1 or more, more or less regularly hexagonal or
rhomboidal, limbidium distinct or not, sometimes partially bistratose;
capsules mostly nodding, more or less symmetric, spore sizes various
……………….... 8 8.
Stems comose or evenly foliate, not distinctly rosulate; leaves ovate to
ovate-lanceolate or lanceolate, widest at or below middle of leaf, lamina
margins smooth to finely serrulate but not strongly serrate, border
unistratose or bistratose; rhizoidal tubers lacking, leaf axis filiform
gemmae rarely present; costa Bryum-type;
monosetous; terricolous or saxicolous …………………………..………...... Bryum (Bryum sect. Amblyophyllum, Penduliformia, Caespitibryum) 8.
Stems rosulate, at least fertile ones, sometimes innovations evenly foliate;
leaves obovate or oblong to spathulate, widest above middle, lamina margins
serrulate to distinctly serrate, unistratose; rhizoidal tubers and leaf axis
filiform gemmae often present, costa Bryum or Rhodobryum-type
various; monosetous or polysetous; habitats various, rarely
epiphytic-corticolous ………………………….. 9 9. Leaves mostly
medium to large, upper margins usually serrate to serrulate at apex, stolons
absent, costa Bryum-type; rhizoidal
tubers generally present, filiform gemmae sometimes present in leaf axils;
micronemata common on stem; on various substrates including bark of living
trees ………….. Rosulabryum 9.
Leaves mostly robust, upper margins distinctly serrate, stolons sometimes
present, costa Rhodobryum-type; gemmae
lacking; stems lacking micronemata; terricolous ….. 10 10. Lamina finely
rugose, cells large, 90—150 µm long by 30—50
µm wide, costa not reaching apex; stolons absent …………….
Roellia 10. Lamina smooth,
cells mostly <100 µm long and <35 µm wide; costa not reaching apex,
percurrent or excurrent; stolons present ……………..
Rhodobryum For keys to
genera, sections and species of Bryaceae, click |