98 



LEMNACEiE. 



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

 commonly 2, orbicular to obovate, slightly to very unsymmetrical, 

 usually 3 to 5-nerved, 1 to 2 lines wide, 1 to 2£ lines long, thick, 

 convex and slightly keeled above, flat to strongly gibbous beneath; 

 base usually acute and commonly with narrow wing margins; pistil 

 clavate; ovules 1 to 7; fruit symmetrical, purple-tinted, winged with 

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



Abundant in ponds. 



2. L. minor L. Smaller 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 clavate; 

 ovule 1; fruit not winged, projecting about ^ beyond the margin of 

 the frond. 



Covering the surface of stagnant ponds. Variable. 



3. L. trisulca L. Ivy-leaved Duckweed. Fronds forming 

 dense masses, oblong to oblong-lanceolate, slightly unsymmetrical and 

 frequently a little falcate, 1\ to 5 lines long and \\ lines wide, the 

 long stipe attached to the basal margin; floating fronds with shorter 

 stipes and cavernous throughout the central portion; submerged fronds 

 with long twisted stipes; seed prominently 12 to 15-ribbed. 



Cold springs and running water. 



4. L. cyclostasa (Ell.) Chev. Fronds solitary or more commonly 

 2 to 8 cohering in a more or less curved chain, thin, oblong to 

 obovate-oblong, usually somewhat falcate, \ to f lines wide by 1 to \\ 

 lines long, without papillae; base of the frond usually unsymmetrical, 

 tapering into a short stipe or frequently sessile; fruit long-ovate, 

 pointed by the long, straight or rarely curved style; seed 12 to 

 29-ribbed. 



Springs at foot of Uncle Sam Mountain, Lake Co., Bolander. 



5. L. minima Phil. Fronds cohering in twos, sometimes in fours, 

 or solitary, oblong to elliptical, symmetrical, £ to 1^ lines wide, f to 

 2 lines long, rather thick, with a row of papilla? along the mid-nerve; 

 lower surface flat or slightly convex, upper surface slightly to promi- 

 nently convex with thin margin entirely around the frond; frond 

 cavernous in the middle portion only, commonly nerveless; seed 

 oblong, pointed, about 16-ribbed. 



Two growth stages; smaller fronds straw-yellow or pale green and 

 strikingly convex on the upper surface; larger fronds thinner and 

 green colored. 



2. WOLFF I A Horkel. 

 Very minute plants. Fronds rootless, thin, unsymmetrical, curved 

 in the form of a segment of a band, abundantly punctate on both 

 surfaces with brown epidermal pigment cells. Stipe attached on the 

 margin of the single reproductive pouch which appears as a cleft in 

 the basal margin of the frond. Flowers and fruit unknown. (J. F. 

 Wolff, student of the genus Lemna.) 



