BFNA Title: Leucobryaceae
Author: P. L. Redfearn, Jr.
Date: April 2000
Edit Level: Q
Version: 3

Bryophyte Flora of North America, Provisional Publication
Buffalo Museum of Science
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LEUCOBRYACEAE W. P. Schimper
Paul L. Redfearn, Jr.
version 3

Plants in small to large cushions, white to pale green, glaucous, grayish or pale brown. Stems erect, branching, central strand absent or poorly developed. Leaves thick, consisting mostly of an expanded costa, distal part of leaf (limb) linear, ligulate or lanceolate, tubulose, spreading from a narrow base (sheath); costa consisting of 2--several layers of enlarged empty, hyaline, thin-walled, porose cells (leucocysts) enclosing a central layer of small, green cells (chlorocysts); unistratose lamina restricted to leaf base, consisting of very narrow, delicate, hyaline, quadrate to oblong or linear cells. Sexuality: Dioicous, pseudautoicous, or autoicous. Seta terminal, straight. Capsule erect to inclined, symmetric or asymmetric, often strumose; operculum long-rostrate, often longer than urn; annulus present or absent; peristome teeth 8--16, entire or divided 2 their length, articulate. Calyptra cucullate or mitrate, smooth, rarely fringed at base. Spores spherical.

Genera 8, species ca. 155 (1 genus and 2 species in the flora): temperate, tropical, worldwide.

Species of Leucobryaceae are characterized by plants with thick, whitish leaves consisting mostly of an expanded costa and a narrow basal lamina. The actual number of genera in this family is uncertain. Current attributions range from one (Eddy 1990) to four (Vitt 1982) to eight (Robinson 1985). Because of its peculiar peristome, Octoblepharum is placed in the Octoblepharaceae by Eddy (l.c.) and in the Leucophanaceae by Reese (1998, personal communication).

The Leucobryaceae have been sometimes included in the Dicranaceae because of similar costal modifications in Brothera, Campylopus, and Paraleucobryum and a peristome structure identical with that of Dicranum (Crosby and Magill 1977). Robinson (1985) suggests that in large part the characteristic pale color of Leucobryum is caused by air bubbles in the leucocysts, and the presence of air in the leaf is assumed to be characteristic of the Leucobryaceae. Furthermore, he concludes that "such bubbles are necessary for the function of the chlorocysts, which are remote from the surface of the leaf, and which could not properly exchange gases if the leucocysts were all filled with water."

 SELECTED REFERENCES Allen, B. 1994. Moss Flora of Central America. Part 1. Sphagnaceae--Calymperaceae. Monogr. Syst. Bot. 49. Missouri Bot. Gard. Andrews, A. L. 1947. Taxonomic notes VI. Bryologist 50: 319--326. Crosby, M. R. and R. E. Magill. 1977. A Dictionary of Mosses. Missouri Bot. Gard., St. Louis. Crum, H. and L. E. Anderson. 1981. Mosses of Eastern North America. 2 vols.New York. Eddy, A. 1990. A Handbook of Malesian Mosses, vol 2. Leucobryaceae to Buxbaumiaceae. Nat. Hist. Mus. Publ., London, pp. 4--21. Robinson, H. 1985. The structure and significance of the leucobryaceous leaf. Monogr. Syst. Bot. Missouri Bot. Gard. 11: 111--120. Robinson, H. 1990. A functional evolution of the Leucobryaceae. Tropical Bryology 2: 223--237. Vitt, D. H. 1982. Bryopsida, pages 307--336 in S. P. Parker, Ed.-in-chief, Synopsis and Classification of Living Organisms. New York and other cities. Yamaguchi, T. 1993. A revision of the genus Leucobryum (Musci) in Asia. J. Hattori Bot. Lab. 73: 1--123.
 

1. LEUCOBRYUM Hampe, Flora 20: 282. 1837  •  Greek leuco, white, and bryum, a moss

Plants in compact to loose cushions or turfs. Stems 0.5--15 cm tall. Leaves crowded, limb lanceolate or subulate-lanceolate and concave to subtubulose, erect, spreading, reflexed to flexuose or falcate-secund, little changed when dry, spreading from an oblong-obovate to elliptic sheath; costa consisting of 1--4 layers of abaxial and 1--4 layers of adaxial leucocysts that enclose a central layer of quadrate chlorocysts; inner walls of leucocysts with single pores; external pores often present on the abaxial surfaces of the cell walls of leucocysts in the apical and basal regions of leaves. Asexual reproduction by means of small, caducous, leaf-like gemmae and by leaves with rhizoids borne adaxially on exposed chlorocysts at the leaf apex. Sexuality: Pseudautoicos, with dwarf male plants growing on tufts of tomentum or leaves of female plants. Seta 1, occasionally 2. Capsule inclined, asymmetric, plicate when dry, often strumose; operculum long-rostrate; annulus usually absent; peristome teeth 16, divided 1/2 their length, vertically pitted-striolate below, papillose above. Calyptra cucullate, often split incompletely to the base which clasps the tip of seta until capsule matures. Spores yellowish or brownish, nearly smooth to minutely papillose. n = 6--11 (Fritsch 1991).

Species ca. 122 (2 in the flora): temperate, tropical, worldwide.

Based on an analysis of ten separate characters of the leucobryoid leaf, Burch (1997) has suggested the possibility that the genus Leucobryum may not be phylogenetically homogeneous, but that possibility remains to be evaluated.

The external pores of the leucocysts can be demonstrated by staining with safranin.

1. Plants in low, compact cushions or turfs; stems less than 1 cm tall (rarely to 4.5 cm); leaves 2--4(--6) mm long, limb subtubulose, erect to wide-spreading, straight, shorter than (rarely equal to) the length of sheath   1. Leucobryum albidum

1. Plants in tall, compact cushions or turfs; stems mostly 1--12.5 cm tall (rarely shorter); leaves mostly 3--9 mm long, the limb concave to subtubulose, erect-spreading, sometimes falcate-secund, 1--2(--3) times the length of sheath       2 . Leucobryum glaucum

1. Leucobryum albidum Bridel ex Palisot de Beauvois) Lindberg, Öfvers. Förh. Svenska Vetensk.-Akad. 20: 403. 1863

Dicranum albidum Bridel ex Palisot de Beauvois, Prodr. Aethéog. 52. 1805

Plants in low, compact cushions or turfs. Stems less than 1 cm tall (rarely to 4.5 cm), Leaves 2--4(--6) mm long, limb subtubulose, erect to wide-spreading, straight, apex apiculate, entire, speading from an oblong-obovate sheath, shorter than (rarely equal to) the length of the sheath; costa in transverse section near base showing lateral, thicker regions composed mostly of 2(--3) layers of enlarged leucocysts above and below the central layer of chlorocysts, and a central, thinner region composed of 1 layer of smaller leucocysts above and below chlorocysts; lamina narrow, 8--11 cells wide. Asexual reproduction by small leaf-like gemmae on minute, forked branches at stem tip or on pseudopodium-like branches and by caducous leaves with rhizoids at leaf apex. Seta 8--12 mm long, brown to reddish. Capsule strongly inclined and curved when dry and empty, sometimes slightly strumose, 1.2--1.8 mm long, red to reddish-brown; operculum 1--1.3 mm long; peristome teeth dark red. Calyptra ca. 2 mm long. Spores minutely papillose, 11--16 µm. n = 6 (Anderson and Bryan 1958).

Mature spores present August to January. On moist humus, sandy soil, rotting logs and stumps, tree bases, hardwood trees, pine and palms, in forests, bogs, and swamps. 0-1000 m. Ont.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Vt., Va., W.Va. Wisc.; Mexico (Tamaulipas), Central America and the Greater Antilles. Reported from Bermuda.

Small, low cushions, usually no more than 10 cm in diameter are characteristic for L. albidum. Plant frequently bearing sporophytes. Of the 1035 collections examined, 632 (61 percent) had sporophytes.

Leucobryum albidum is sometimes difficult to separate from small plants of L. glaucum. Some authors have used the number of leucocysts, as seen in transverse section, above and below the chlorocysts on thicker, lateral regions of the costa to separate these species. However, this character varies widely on plants from the same colony and even on different sides of the same leaf. Furthermore, there is no consistent pattern for these species across their geographical range and correlation with other characters such as stem height and length of limb to length of sheath is inconclusive. The most satisfactory criteria for recognizing L. albidum are its generally compact, short cushions and leaves 2--4 mm long with a reflexed limb usually shorter than the sheath. Patterson, Boles & Shaw (1998) in a study of Leucobryum from a limited area near Durham, NC, using nuclear ribosomal DNA extracts from plants of various sizes, demonstrated that two haplotyes were present and that L. albidum (small plants) is genetically discontinuous with L. glaucum (large plants).

Leucobryum incurvifolium J. K. A. Müller [= Terrestria incurvifolia (J. K. A. Müller) W. L. Peterson] is reported from Florida (Peterson and Sharp 1980). However, the two collections cited from Florida appear to be nothing more than a variation of L. albidum. They do not have the distinct cucullate hyaline-apiculate leaf tips characteristic of L. incurvifolium (Peterson 1994).

2. Leucobryum glaucum Hedwig) Ångstrom, Summ. Veg. Scand. 1: 94. 1846.

Dicranum glaucum Hedwig, Spec. Musc.: 135 (1801)

Plants in tall, compact cushions or turfs. Stems 1--12.5 cm tall (rarely shorter). Leaves 3--9 mm long, limb concave to subtululose, erect or erect-spreading, sometimes falcate-secund, apex acute or apiculate, usually+ serrulate at the tip, spreading from an oblong-obovate sheath, 1--2(--3) times the length of sheath; costa in transverse section near base showing lateral, thicker regions composed mostly of 2--3(--4) layers of enlarged leucocysts above and below the central layer of chlorocysts and a central, thinner region composed of 1 layer of smaller leucocysts above and 2 layers below chlorocysts (or vice versa), occasionally with only 1 layer of leucocysts above and below chlorocysts; lamina narrow, 5--11 cells wide. Asexual reproduction by clusters of small caducous leaf-like gemmae at stem tip and by leaves with rhizoids at apex. Seta 8--18 mm long, reddish. Capsule strongly inclined and curved when dry and empty, usually strumose, 1.5--2 mm long, red to reddish-brown; operculum 1.5--2 mm long; peristome teeth dark red. Calyptra ca. 2 mm long. Spores nearly smooth to minutely papillose, 13-18 µm.

Mature spores present August to December. On humus, soil, rotting logs and stumps, tree bases, and rock ledges in forests, bogs, and swamps. 0--1800 m. Alta.?, Man., N.B., Nfld., N.S., Ont., P.E.I., Que.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Vt., Va., W. Va., Wis.; Europe, Transcaucasia, the Caucasus, Japan and China. Reported from Canary Islands and Madeira. The collection from Alberta [Drummond's Musci Americani 89 (UT)] is probably incorrectly labeled as to locality.

Large tall cushions are distinctive for L glaucum and under favorable circumstances some cushions may exceed 1 m in diameter. The separation of smaller, shorter plants from L. albidum is difficult. The use of the number of layers of leucocysts above and below the chlorocysts is highly variable and not a reliable distinguishing feature. The ratio of length of the sheath to the length of the limb provides the most consistent way to separate L. glaucum from L. albidum. Sporophytes are infrequently observed. Of 1933 collectons examined, 308 (16 percent) had sporophytes. Most of the plants with sporophytes were from collections located north of the Ohio River.

Leucobryum antillarum W. P. Schimper ex E. Bescherelle var. antillarum has been reported from the Coastal Plain of the United States based upon plants that had only 1 layer of leucocysts above and below the chlorocysts across a wide section of the median portion of the leaf as seen in transverse section near the base. However, this character is quite variable and not even consistent in L. antillarum (Crum and Anderson 1981). Furthermore, plants from the coastal plain do not show the prorate cells on the lateral wings of the lamina that are present in the type material of L. antillarum.

OTHER REFERENCES

Anderson, L. E. and V. S. Bryan. 1958. Chromosome numbers in mosses of eastern North America. J. Elisha Mitchell Sci. Soc. 74: 173--199.

Burch, J. 1997. The leucobryoid leaf. Bull. Brit. Bryol. Soc. 69: 24--25.

Fritsch, R. 1991. Index to bryophyte chromosome counts. Bryophyt. Biblioth. 40. Berlin.

Patterson, E., S. B. Boles and J. Shaw. 1998. Nuclear ribosomal DNA variation in Leucobryum glaucum and L. albidum (Leucobryaceae): a preliminary investigation. Bryologist (In press).

Peterson, W. 1994. Leucobryaceae. pp. 169--186. In: A. J. Sharp et al., eds. The Moss Flora of Mexico, New York.

Peterson, W. L. and A. J. Sharp. 1980. Leucobryum incurvifolium in the United States. Bryologist 83: 370--371.

Version History for Leucobryaceae
Version 3: April, 2000 -- illustration added
Version 2: March, 1999 -- maps added, minor editorial changes.
Version 1: February, 1999