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BFNA Title: Rivulariella |
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RIVULARIELLA -- JUNGERMANNIACEAE 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. |
