Riccia fluitans L.

Riccia fluitans I.. Sp. PI. 1139. 1753
11. i?. glauca.
12. R. arvensis.
13. R. Campbelliana^
14. R. nigrella.
15. R. violacea.
16. R. McAllisteri.
17. R. subplana.
18. R. EllioUii.
19. R. dictyospora.
20. R. albida.
21. R. Beyrichiana..
22. R, hirta.
23. R. californica,
24, R. trichocarpa.
25. R. Donnellii.
Riccia canaliculata Hoffm. Deuts. Fl. 2: 96. 1796.
Riccia fluitans canaliculata Roth, Fl. Germ. 3': 434. 1800.
Ricciella fluitans A. Br. Flora 4: 757. 1821.
Riccia eudichotoma Bisch. Nova Acta Acad. Leop.-Carol. 17: 1068. 1835.
Thalli floating or suspended in water or creeping on moist soil, 1-5 cm. long, repeatedly and regularly dichotomous, carinate-costate, green dorsaUy and ventrally, the dorsal surface smooth, often wrinkled on drying, occasionally lacunose with age; root-hairs almost wanting in aquatic conditions; main segments narrowly linear, 0.5-1.5 mm. broad; terminal segments. oblong to linear, obtuse or subtruncate, emarginate; margins mostly flat, ascending in terricolous conditions, 2 or 3 cells thick or more or less unistratose; median sulcus shallow, observable only near apex except in land forms; scales deficient, or, in terricolous forms, rudimentary, sometimes violet ; transverse sections often biconvex, mostly 2-4 times as broad as the maximum height; dorsal epidermis unistratose, persistent, occasionally collabent and disintegrated over air-chambers with age, the cells mostly 40-90 ju in maximum diameter in terricolous forms and showing small stomatal pores, in aquatic forms 50-200 ju long and without obvious pores; a^r-chambers large, elongate-polyhedral, separated by unistratose lamellae and showing 1-3 series in a tranverse section. Monoicous; antheridial ostioles elevated 75-150 m; capsules (found only in terricolous or semiterricolous conditions) forming hemispheric or subglobose protuberances 450-600 ju in diameter on the ventral surface; spores yellowish-brown, translucent, 65-104 fj. in maximum diameter, angular, with a margin 3-8 n wide, the outer face with rather smooth areolae 12-25 fi broad, the larger often enclosing a free-ending spur or an isolated tubercle, 4 or 5 areolae measuring the width of the face, the inner faces with short free or irregularly anastomosing ridges.
Type i^ocality: Europe.
Distribution: Quebec and British Columbia to California ; Costa Rica ; Cuba ; Haiti; Jamaica; cosmopolitan.
lLLUSTRATiONs:Nova Acta Acad. Leop.-Carol. 17: pi. 70, f. V; 18: pi. 24, 25,-3Leitgeb, Unters Leberm. 4: pi. 1, f. 11-15; pi. 2, f. 1-3; Krypt.-fl. Brand. I: 79. /. 8; Pearson, Hep. Brit. Isles pi. 224; Rab. Krypt.-Fl. 6;/. tf, 134.

Riccia fluitans, the floating crystalwort, is an aquatic floating plant of the liverwort genus Riccia which is popular among aquarists as a retreat for young fry and is used in live-bearing tanks. It can be found floating in ponds, and often forms thick mats on and under the water surface.

It normally grows quickly at the surface. When kept about two to three inches below an ordinary fluorescent bulb or in a pond exposed to full sunlight, it will form dense, bright green mats. Any single branch or antler bud can reproduce into a large colony if the plant is kept in proper conditions. It normally floats, but can also be attached to underwater objects such as logs and rocks. It can be attached with plastic mesh.

Floating crystalwort is generally not compatible with duckweeds, as they cover the surface of the water quite rapidly, crowding the Riccia out. It is also easily overtaken by hair algae.

The species epithet fluitans is Latin for floating.