LEMNACEJE. 



1)7 



Calistoga, Lower Sacramento and southward to Santa Clara Co. 

 June-July. 



S. simplex Huds. SAMPLE Bur-rkkd. 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; they 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 Mr. Chas. 

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

 Botanical Garden. 



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; papilla 



none 3. L. ti-isulca. 



Frond with a short stipe, floating on the surface. 

 Symmetrical or nearly so, papillate along the median line. 

 Obion g-obovate; 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 b. L. minima. 



Unsymmetrical, 



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



line 1. L. gibba. 



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



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