1. Wolffia Columbiana Karst. Fig. 295. 



Thallus solitary or paired, globular or rarely ellipsoidal, 0.8-1.4 mm. long, 

 0.4-0.8 mm. wide, scarcely if at all flattened, green on all surfaces, not conspicu- 

 ously punctate, the dorsal surface not flattened and without a papilla. 



On lakes and sloughs of Okla. (Choctaw and McCurtain cos.) and e. and s. Tex.; 

 from N. E. to Calif., s. to n. S.A. 



2. Wolffia papulifera Thomps. Fig. 295. 



Thallus solitary or paired, mostly broadly ovoid, 0.5-1.5 mm. long, 0.3-1 mm. 

 wide, green, brown-punctate on all surfaces, the dorsal surface flattened and 

 bearing a conspicuous papilla. 



On surface of lakes and ponds in Okla. (Choctaw and McCurtain cos.) and in 

 e. Tex. and on the Edwards Plateau; from Va. s. to Fla., w. to Tex., Kan. and 111. 



3. Wolffia punctata Griseb. 



Thallus ellipsoid to ovoid-oblong, usually tapering to an acutish apex, 0.7-1.2 

 mm. long, 0.4-0.7 mm. wide, the dorsal surface flattened and without a papilla, 

 punctate on all surfaces with brown pigment cells. 



In marshes, lakes and sloughs in s.e. Okla. (McCurtain Co.) and e. Tex. (Bowie, 

 Cherokee, Harrison and Henderson cos.); from Conn, to Ont. and Minn., s. to 

 Tex. and the W. I. 



4. Wolffiella Hegelm. Mud-midget. Bog-mat 



Thalluses flat, thin, membranous, elongate or straplike, frequently falcate, soli- 

 tary or commonly 2 remaining attached, sometimes many remaining connected to 

 form extensive colonies, rootless, usually floating submersed except for a small 

 area at the base, more or less punctate with brown pigment cells in epidermis of 

 all surfaces, commonly reproducing by budding from a single triangular (in out- 

 line) basal pouch, rarely flowering; flowering cavities on dorsal surface at one 

 side of median line; flowers not enclosed in a spathe, unisexual, consisting of a 

 single stamen or a single pistil, the pistillate flower with a single orthotropous 

 ovule; fruit a slightly laterally compressed utricle with the style persistent; seed 

 smooth, with spongy outer coat, the prominent operculum flattened. 



About 8 species, primarily in the New World. 



1. Thallus Ungulate (tongue-shaped), strongly curved, up to 4 times as long as 

 wide, usually 2 attached to form a circle 1. W. lingulata. 



1. Thallus more or less sickle-shaped, mostly 5 times or more longer than wide, 



usually several to many cohering in colonies (2) 



2(1). Thallus broad at base, abruptly tapered to the obtuse-rounded apex, slightly 

 falcate 2. W. gladiata. 



2. Thallus narrow at base, gradually tapered to a slender sharp point, usually 



doubly falcate 3. W. floridana. 



Fig. 294: Lemna gibba: a, roots, with and without rootcap, X 12; b and c, winged 

 fruits, the ovules 1 to 3,- X 12; d-f, mature seeds, showing corky ribs and conspicuous 

 operculum, X 16; g, young seed, X 16; h, staminate and pistillate flowers surrounded 

 by saclike spathe, X 23; i, flowers with spathe removed, showing the pistillate flower 

 with winged shoulders and a pair of staminate flowers, X 25; j, flowering and fruiting 

 fronds with inflated gibbous lower side and solitary roots, X 2; k and 1, fronds (longi- 

 tudinal section), showing variation in the air spaces, X 8; m, habit, top view of flower- 

 ing fronds, X 4; n, habit, top view of fronds, the parent frond with fruit, X 4. o-w, 

 non-gibbous plants; o-q, fronds (longitudinal section), X 8; r, habit, flowering fronds, 

 X-4; s and t, pistillate and staminate flowers surrounded by spathe, X 28; u, habit, 

 showing group of plants, X 2; v and w, roots, with and without rootcap, X 20. (From 

 Mason, Fig. 160). 



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