Riccia glauca L.

Riccia glauca L. Sp. PI. 1139. 1753
Thalli medium-sized, 6-10 ram. long, 2-4 times dichotomous, at first subradiate, later confluent and irregularly gregarious, reticulate, light-green or subglaucous above, concolorous or rarely blackening below; main segments oblong or obcuneate, mostly 1.5-2.5 mm. wide; terminal segments subquadrate, linguiform, or obovate, obtuse, subtruncate, or emarginate-
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retuse; margins acute or subobtuse, mostly rather thin, usually ascending, naked; median sulcus broad and obtuse, occupying one third or more of the width of the thallus, soon vanishing toward base; scales inconspicuous, colorless or rarely darkening; transverse sections oblong, subelliptic, or crescentic, mostly 4-5 times as broad as high, 15-25 cells thick in median parts, the ventral outline lightly convex or nearly rectilinear; dorsal epidermis 2-stratose, the cells of the primary stratum hemispheric-ellipsoid or ovoid, obtuse or conic-mammillate, soon collapsing and leaving imperfect cups or irregular vestiges, the cells of the succeeding stratum mostly 30-80 y. broad, commonly broader than high. Monoicous; antheridial ostioles elevated 75-160 /i; capsules usually numerous, long included; spores brown, 75-118 m in maximum diameter, angular, with a smooth or subgranulate, more or less crenulate margin 5-13 y. wide, the outer face areolate, showing in profile obtuse papillae 1-5 m long, the areolae mostly 8-13 ix wide, the inner faces similarly but less strongly marked.
Type locauty: England.
Distribution: California and Texas; also in Europe.