LEMXACE^. 97 



Calistoga, Lower Sacramento and southward to Santa Clara Co. 

 June-July. 



S. SIMPLEX Huds. Simple Bur-reed. Stems slender, simple, 

 erect, 1 to 2 ft. high; leaves triangular or flattened, exceeding the 

 stem; heads 2 to 4 of each kind, sessile or the lower often on a pedun- 

 cle J to 2 in. long and above the axil; staminate heads very small; 

 nuts nearly terete, attenuate at each end, tipped with a linear style, 

 the whole 3 or 4 lines long. — Sierra Nevada: Placer Co., Carpenter; 

 Carson Pass, Brewer. 



7. LEMNACE/E. Duckweed Family. 



Minute floating or submerged aquatic perennials, without leaves. 

 Plant body consisting of a leaf-like stem or " frond " which is densely 

 green, disk-shaped, elongated or irregular. Inflorescence a simple 

 cluster of 2 staminate flowers and 1 pistillate flower, contained in a 

 cleft or pouch on the margin of the frond. Staminate flower consist- 

 ing of a single stamen and the pistillate flower of a single ovary con- 

 taining 1 to 7 ovules. Perianth none. Flowers and fruit scarce, in 1 

 species unknown. Vegetative reproduction active and taking place 

 by lateral branching, the branches being attached by slender stalks 

 (stipes). These branches soon separate or remain connected for some 

 time; the}- may at certain seasons sink to the bottom of the pond or 

 ditch and undergo a resting period. The account of genera and 

 species here given has been adapted almost entirely from ^[r. Chas. 

 H. Thompson's Kevision published in the 9th Report of the Missouri 

 Botanical Oarden. 



•Frond with 1 to several nerves and a single root; ovules 1 to 7 . .1. Lemna. 

 Frond without nerves; root none; ovule 1 . . . . . . . 2. Wolffia. 



1. LEMNA L. Duckweed. 

 Fronds disk-shaped, usually with a central nerve and with or with- 

 out 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 contain- 

 ing a cluster of 3 flowers surrounded by a spathe. Ovary with 1 to 7 

 ovules. Fruit ribbed. (Ancient Greek name.) 



Frond with a long stipe, mostly submerged and forming large masses; papillae 



none 3. X. tr&iUca. 



Frond with a short stipe, floating on the surface. 

 Symmetrical or nearly^ so, papillate along the median line. 

 Obloiie-obovate; fruit more or less lenticular. 

 Upper surface unirormly green; margin of the fruit without appendages; 



seed- always 1 2. L. mvnor. 



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



with rounded wing lobes; seeds 1 to several l.L.gOiba. 



Oblong to elliptical, small, green on both surfoces; with a row of papillae 



along the mid-nerve; fruit elongated . . 5. Z. minima . 



Unsymmetrical , 

 Obliquely obovate; obscurely 3 to 7-nerved, papillate along the median 



line X. L. gihba. 



Long oblong, thin, obscurely l-nerved; papillae none . . . 4 i. eycloslasa. 



9 



