BFNA Title: Brachelyma
Author: B. H. Allen
Date: October 2, 2009
Edit Level: R
Version: 1

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden
BFNA Web site: http://www.mobot.org/plantscience/BFNA/bfnamenu.htm

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XX. BRACHELYMA Schimper ex Cardot, Mém. Soc. Sci. Nat. Cherbourg 28: 130. 1892 * [Greek brachys, short, and elyma, veil, alluding to diminutive calyptra]

Bruce H. Allen

Plants slender to medium-sized, submerged or seasonally inundated. Stems prostrate or pendent, irregularly branched, in cross section with a very thick scleroderm, firm-walled cortical cells, no central strand; axillary hairs 240--360 \um, basal 1--3 cell(s) subrectangular, reddish brown, distal 3--5 cells oblong, hyaline; rhizoids from clusters of initials abaxial to the leaf insertions, not or weakly branched. Leaves 3-ranked, crowded and imbricate, distant and erect to erect-spreading, keeled and conduplicate, oblong-lanceolate to lanceolate, obtuse to acute, decurrent; margins entire or serrulate proximally, serrulate to serrate at apices, at times narrowly reflexed; median leaf cells rhomboidal, linear-rhomboidal or elongate; marginal cells linear, forming a weak border; alar cells firm-walled, quadrate or rectangular, not or slightly enlarged, costa usually subpercurrent to percurrent. Sexual condition dioicous; perigonia gemmate, lateral in leaf axils, perigonial leaves ecostate, antheridia few (4--5), paraphyses present; perichaetial leaves elongate, sheathing the setae, archegonia numerous, paraphyses present. Seta short, surface cells quadrate. Capsule immersed, oblong-cylindrical to oval; operculum long-conic at times obliquely beaked; annulus massive; stomata absent; peristome with exostome teeth inserted, shorter than endostome, linear, orange or red, trabeculae widely spaced, papillose, more strongly thickened on the inner surface than the outer surface; endostome segments linear, red to brownish-orange, papillose, joined by lateral bars only at the apex (trellis imperfect). Calyptra cucullate, covering only the operculum.

Species 1: southeastern and central North America.

Brachelyma is a monotypic genus endemic to eastern North America. It is semi-aquatic and found primarily in dense, often pendent, masses on tree trunks and branches, but also rocks, logs, and roots, along rivers, streams, and sloughs where the plants are submerged during periods of high water, but dry the rest of the time. As with many other semi-aquatic mosses Brachelyma is variable in size and its plants can be slender to almost robust. Distinctive features include long, narrow, keeled-conduplicate, at times obscurely bordered leaves; strong, single costae; firm-walled, non-bulging alar cells; serrate to serrulate distal leaf margins; often rhomboidal distal leaf cells; long, sheathing perichaetial leaves, and short setae with completely immersed capsules. Curiously the surface cells of the setae are quadrate to oblate; the result of simple cell elongation in these cells would give the Brachelyma setae the same length as the Dichelyma setae, as well as immersed or exserted capsules. Brachelyma has an imperfect endostome with the segments only united at the tips. The calyptrae are intermediate in size between those of Fontinalis and Dichelyma, and have the cucullate form of Dichelyma, but like those of Fontinalis, only cover the operculum.

SELECTED REFERENCES Cardot, J. 1892. Monographie des Fontinalacées. Mém. Soc. Sci. Nat. Cherbourg 28: 1--151. Welch, W. H. 1960. A monograph of the Fontinalaceae. The Hague. Welch, W. H. 1963. Fontinalaceae. N. Amer. Fl. II, 3: 1--51.

1. Brachelyma subulatum (Palisot de Beauvois) Cardot, Mém. Soc. Sci. Nat. Cherbourg 28: 130. 1892

Fontinalis subulata Palisot de Beauvois, Prodr. Aethéogam. 58. 1805; Dichelyma subulatum (Palisot de Beauvois) Myrin; Brachelyma robustum (Cardot) E. Britton

Plants green, yellowish green to brown, dull. Stems to 30 cm, irregularly branched. Leaves 2--4 mm; median leaf cells 10--60 x 5--8 \um, marginal cells 60--120 x 6--8 \um; alar cells quadrate or rectangular, slightly enlarged, costa subpercurrent to percurrent. Perichaetial leaves ovate-lanceolate to linear-lanceolate, 2--4 mm, acute to long-acuminate, entire, ecostate. Seta 0.7--1.5 mm. Capsule 1.5--2.5 mm; operculum 0.5--1.2 mm; annulus of 8--9 rows of thick-walled cells, persistent on capsule mouth after dehiscence. Calyptra smooth, naked, 2--3 mm. Spores 13--18 \um, minutely roughened to smooth.

Tree trunks, branches, roots, bushes, logs, soil, and rocks along rivers or in flood plains and sloughs, subject to inundation; 4--271 m; Ala., Ark., Fla., Ga., Ill., Ind., Ky., La., Md., Miss., Mo., N.C., Okla., S.C., Tenn., Tex., Va.

Brachelyma subulatum differs from all Fontinalis species in having costate leaves and cucullate calyptrae. Usually the presence of costate leaves is enough to separate the two genera, but costal expression in Brachelyma is sometimes variable and appears to be environmentally induced. It is not unusual to find plants with keeled, strongly costate proximal leaves but concave, ecostate or weakly costate apical leaves. Brachelyma subulatum has been noted as lacking an annulus, but in fact it has massive, persistent annulus quite similar to the annulus found in many genera of the Hookeriales. Dichelyma differs from Brachelyma subulatum only in having longer setae and larger calyptrae that completely cover the capsule and often clasp the distal portion of the seta. Brachelyma subulatum appears to be only a weak segregate of Dichelyma. In the absence of prior experience with Brachelyma subulatum, the species could be confused with many other aquatic or semi-aquatic mosses. But, B. subulatum differs from all of such mosses in having keeled-conduplicate leaves.