Fissidens Moss

Fissidens hyalinus (Latin hyalus, literally “of glass,” alluding to the transparent, glasslike appearance) is doubtless more common than previously thought. B. E. Lemmon (1966) published a photograph showing a perigonial stem and a perichaetial stem with attached sporophyte. A. C. Risk (2002) gave a thorough account of the distribution and habitat of this tiny moss. Plants cannot be mistaken for any other species in North America, owing to the ecostate leaves and smooth, large, thin-walled laminal cells that shrink considerably when dry.

Fissidens hyalinus is extremely small and is not easy to locate without keen eyes and experience. It is always found on newly eroded soil banks in shaded sites.

Plants to 3.5 × 3 mm. Stem unbranched; axillary hyaline nodules absent; central strand absent. Leaves as many as 6 pairs, lanceolate, acute to obtuse, sometimes apiculate, to 2.2 × 0.5 mm; dorsal lamina narrowed proximally, ending at insertion, not decurrent; vaginant laminae ¹/3-¹/2 leaf length, equal; margin entire but sometimes ± serrulate distally, limbate, limbidium 1-2 cells wide, ending before apex, often indistinct on vaginant laminae, limbidial cells 1-stratose; ecostate, or costa consisting of very short proximal vestige; laminal cells 1-stratose, smooth, thin-walled, hexagonal to elongate-hexagonal, 31-67 × 14-34 µm, ± oblong in proximal portions of leaves, particularly in vaginant laminae. Sexual condition rhizautoicous; perigonia gemmiform, proximal to perichaetial stems, and on elongate stems, to 1.2 mm. Sporophytes 1 per perichaetium. Seta to 3 mm. Capsule theca exserted, erect, radially symmetric, sometimes slightly arcuate, bilaterally symmetric, to 0.4 mm; peristome scariosus-type; operculum ± as long as theca. Calyptra mitrate, prorate, 0.4 mm. Spores 9-13 µm.

Plants very small, delicate, pale green, loosely gregarious. Leafy stems simple, 1.2–3.2 mm long, 0.8–3.0 mm wide; axillary hyaline nodules not differentiated; central strand lacking. Leaves in 2–5 pairs, densely arranged, upper leaves much larger than lower leaves, oblong-lanceolate to oblong-ovate, 0.6–1.4 mm × 0.2–0.6 mm, acute at the apex; base of dorsal laminae rounded, vaginal laminae nearly 1/2 the leaf length; costa absent; margins plane, entire, bordered throughout by 1–2 rows of elongate cells; cells of apical laminae quadrate to irregularly hexagonal, 35–87 µm long, smooth, thin-walled; cells of vaginant laminae similar to those of apical laminae. Sporophytes unknown.

Distribution: China, Japan, India, North and South America.

Habitat: on moist rocks.

Fissidens hyalinus Wils. & Hook. Jour. Bot. Hook
3:89. 1840.
Conomitrium hyalinum C. Miill. Syn. 2: 525. 1851.
Plants 2-3 mm. high, pale green, hyaline; stems mostly simple; leaves 3-5 pairs, the upper much larger, 1-1.5 mm. long, very thin and soft, oblong-lanceolate, acute, entire, ecostate; leaf-cells oblong-hexagonal, about 30 X 45-60 m, very thin-walled, a single row at the margin narrow and elongated; dioicous; sporophyte terminal; seta 1-2 mm. long; capsule oblong-ovoid, erect and symmetric; calyptra cylindric-conic, covering the beak only; operculum about 1 mm. long, long-rostrate, a little shorter than the urn; peristome normal; spores 11-15 /x in diameter, in autumn.
Type locality: Bank Lick, near Cincinnati, Ohio.
Distribution: On soil and moist rocky ledges in cool shaded ravines, near Cincinnati and near Painesville, Ohio; Washington, Pennsylvania; very rare or overlooked.