DUCKWEED FAMILY 245 



Refs.^SpiRODELA POLYRHIZA Sclileiden, Liniiaea 13:392 (1839). Lemna 2"^hl >'^i >-" L. 

 Sp. PI. 970 (1753), type Eiiropeai). 



2. LEMNA L. Duckweed. 



Fronds 'disk-shaped, usually with a central nerve and with or without several 

 lateral nerves, each with a single root which is commonly provided with a root 

 cap. Reproductive pouches 2, appearing as clefts in either margin of the basal 

 portion of the frond, each containing a cluster of 3 flowers surrounded by a 

 spathe. Ovaiy with 1 to 7 oatiIcs. Fruit ribbed. — Species about 8, all continents. 

 (Ancient Greek name.) 



I'roiul with a long stipe, mostly submerged and foraiing largo masses; papillae none 



3. L. tris^ilca. 

 Frond with a short stipe, floating on the surface. 



Symmetrical or nearly so, papillate along the median line. 

 Oblong-ovate; fruit more or less lenticular. 



Upper surface uniformly green; margin of the fruit without appendages; seed 



always 1 2. L. minor. 



Upper surface mottled with irregular brown streaks; margin of the fruit with 



rounded wing lobes; seeds 1 to several 1. L. gibba. 



Oblong to elliptical, small, green on both surfaces, with a row of papillae along the 



mid nerve; fruit elongated 5. L. minium. 



Unsymmetrieal. 



Obliquely obovate, obscurely 3 to 7-nerved, papillate along the median line—.l. L. gihba. 

 Long oblong, thin, obscurely 1-nerved; papillae none 4. L. cijcJostasa. 



1. L. gibba L. Gibbous Duckweed. Fronds 1 to 4 in a group, commonly 

 2, orbicular to obovate, slightly to very unsymmetrieal, usually 3 to 5-nerved, 

 1 to 2 lines wide, 1 to 21/0 lines long, thick, convex and slightly keeled above, flat 

 to strongly gibbous beneath ; base usually acute and commonly with narrow wing 

 margins; pistil elavate ; ovules 1 to 7 ; fruit symmetrical, purple-tinted, winged 

 with rounded lobes at the upper margin on either side of the stigma. 



Stagnant ponds. All continents except South America. 



Locs. — Pasadena, Compton, Santa Monica Caiion, San Pedro, San Juan Capistrano (Erythea 

 4:195); Mound City, San Bernardino Valley (Ervthea, 7:90); San Francisco (Bot. Cal. 

 2:190). 



Ref. — Lemna gibba L. Sp. PI. 970 (1753), type European. 



2. L. minor L. Sm.\ller Duckweed. Fronds solitary or few in a cluster, 

 round to elliptic-obovate, green or purplish beneath, uniformly bright-green 

 above, convex on both sides, upper surface sometimes slightly keeled and with a 

 row of papillae along the mid-nerve, the apical one usually quite prominent ; 

 pistil elavate ; ovule 1 ; fruit not winged, projecting about % beyond the margin 

 of the frond. 



Stagnant pools, abundant. All continents except South America. 

 Loc. — Lobos Creek, San Francisco (Bot. Cal. 2:190). 

 Eef. — Lemna minor L. Sp. PI. 970 (1753), type European. 



3. L. trisulca L. Tvy-leap Duckweed. Fronds forming dense masses, ob- 

 long to oblong-lanceolate, slightly unsymmetrieal and fre(|ueiitly a little falcate. 

 21/^ to 5 lines long and 1 ' ^ lines wide, the long stipe attached to the basal margin ; 

 floating fronds with sliortcr stipes and cavernous throughout the central portion : 

 submerged fronds with long twisted stipes; seed in-omiiieiitly 12 to l.'5-ribbed. 



Cold springs and niiining water, Sierra Nevada. All continents except South 

 America. 



Locs.— Plumas Co. (Bot. Cal. 2:189); Bouldin Isl. (Zoe, 4:217); San Franci.seo (Bot. Cal. 

 2:189); San Gabriel Creek, San Gabriel Mts. (Bot. Cal. 2:189). 



Ref. — Lemna tmsdlca L. Sp. PI. 970 (1753), type European. 



4. L. cyclostasa f'hev. Fronds solitary or more commonly 2 to S cohering 

 in a more or less curved chain, thin, oblong to obovati'-ol)long, usually somewhat 

 falcate, % to % lines wide by 1 to I14 lines loi'S- without papillae ; base of the 



