BFNA Title: Rivulariella
Author: D. H. Wagner
Date: April 19, 2015
Edit Level: R
Version: 1

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden
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XX. RIVULARIELLA D. H. Wagner, Phytoneuron 2013-10: 2. [Lat. rivularis, of brooklets, plus -ella, diminutive, alluding to habitat]


David H. Wagner


Plants medium-sized, dark. Stems without internal differentiation, little branched, rhizoids scattered on ventral surface. Leaves succubous, emarginate to shallowly lobed, insertion from nearly horizontal to transverse, oil bodies present in all leaf cells. Underleaves small to large, most prominent on erect shoots. Asexual reproduction by fasciculate gemmae produced on leaf margins. Sexual condition monoicous, paroicous or heteroicous. Androecia with 2--3 antheridia per bract, stalks 1-seriate.  Gynoecia terminal on main shoot, bracts and bracteoles larger than leaves, perianth oblong to fusiform, plicate. Sporophyte seta massive; capsule wall several layers thick, outer layer with nodular thickenings, inner layers with semiannular thickenings. Spores greenish when fresh. Elaters mostly 2(--3)-spiral.


Species 1 (1 in the flora): w,nw North America.


Rivulariella is a monotypic genus of the Northwest. It is found attached to pebbles in the bottom of small streams.


SELECTED REFERENCE  Evans, A.  1938.  A new species of Chiloscyphus from Utah.  Bryologist 41: 50--57.


1. Rivulariella gemmipara (A. Evans) D. H. Wagner, Phytoneuron 2013-10: 2. 2013


Chiloscyphus gemmiparus A. Evans. Bryologist 41: 50. 1938


Plants medium sized, shoots to 30 mm, to 4 mm wide, prostrate to ascending, dark green, blackish at base.  Stems slightly to strongly dorsiventrally compressed; prostrate stems flattened, 300--500 \um wide, 150--200 \um high tightly adherent to substrate; stems of ascending shoots more nearly cylindrical, to 400 \um in diameter; branches mainly lateral-intercalary on prostrate shoots, often abundant; branches sparse on ascending shoots, mainly terminal; cortical cell walls thin, 15 x 29 \um, medullary cells 30 x 40 \um with slightly thicker cell walls; rhizoids scattered, abundant on prostrate stems, absent on ascending stems.  Lateral leaves variable 120--150 x 150--200 mm, inserted obliquely and spreading on prostrate shoots, nearly transverse, imbricate and concave on ascending shoots, obovate, rounded or truncate to emarginate or shallowly bilobed.  Median cells subquadrate to elongate-rectangular, rarely hexagonal, 16--18 ´ 17--25 \um, cell walls thin, trigones absent or poorly developed, marginal cells slightly smaller, cuticle smooth.  Oil-bodies (5--)7--12(--20) per median leaf cell, ovoid, 4 x 6 \um, finely granular, colorless.  Underleaves absent or fugacious on prostrate stems, usually small, few celled and multilobed or subulate to lanceolate on ascending stems, with larger underleaves occurring sporadically and randomly, occasionally nearly the same size and shape as the lateral leaves on erect shoots, these shoots virtually isophyllous.  Asexual reproduction by fasciculate gemmae produced along leaf margins at shoot tips, ovoid at maturity, 120--180 x 160--300 \um, composed of 2--4(--6) cells each.  Sexual condition paroicous or heteroicous.  Androecia either below gynoecia or on separate shoots, antheridia in bracteoles of isophyllous shoots on paroicous shoots or in bracts little different from vegetative leaves on anisophyllous shoots when strictly male, spicate or not.  Gynoecia on erect, isophyllous shoots, archegonia developing before perianth formation, perianth exerted 1/2 or more above bracts, inflated, oblong to fusiform, smooth and cylindrical proximally, 4--5 plicate distally, narrowed to an entire or weakly crenulate mouth; perigynium absent. 


Alpine or subalpine zones, strictly confined to small streams fed by cold water springs, attached small stones or pebbles in the stream bed, best developed in full sun; Alaska (Unalaska Island), California, Oregon, Utah, Washington.


The gemmae of Rivulariella gemmipara are abundant in some populations but nearly absent in others. The spores are noticeably green when fresh.  The capsule wall is several cell layers thick, only the outer layer having nodular thickening and the inner cells with semiannular thickenings. Other liverworts commonly found growing with Rivulariella are Jungermannia exsertifolia subsp. cordifolia, Chiloscyphus polyanthos, and Scapania undulata.  Two lichens are also found in this association: Peltigera hydrothyria Miadl. & Lutzoni and Leptogium rivale Tuck.