442 LEMNACE^E. (DUCKWEED FAMILY.) 



with a single amphitropous ovule. Stigma minute, sessile. Fruit green. Seed 

 without albumen. Embryo thick and fleshy. A perennial aquatic herb, with 

 oblong long-petioled leaves, and a yellow erect spadix terminating the club- 



1. O. aquaticum, L. Rhizoma deep, fleshy; leaves acute, nerved, on 

 stout terete petioles ; scape terete, thickened upward, white beneath the spadix, 

 sheathed below, commonly curved. Ponds and slow-flowing streams, Florida, 

 and northward. March and April. Leaves about 1 long. Scape l-2 

 long. Spadix 1' - 2' long ; the upper flowers mostly tetrandrous. 



7. ACORUS, L. CALAMUS. SWEET FLAG. 



Scape flattened, leaf-like, with the lateral sessile spadix covered with the per- 

 fect flowers. Spathe none. Sepals and stamens 6. Corolla none. Filaments 

 slender: anthers kidney-shaped, 1-celled, opening transversely. Ovary 2-3- 

 celled, with several orthotropous suspended ovules in each cell. Stigma minute. 

 Fruit dry, gelatinous within, 1 - few-seeded. Embryo in the axis of the albu- 

 men. Perennial herbs, from a creeping aromatic rhizoma. Leaves erect, long, 

 flattened, 2-edged. Scape leaf-like, elongated above the spadix. 



1. A. Calamus, L. Wet places, Florida, and northward, apparently in- 

 troduced. April. Rhizoma rather slender, pungent. Leaves l-2 high, 

 linear-lanceolate. Scape narrower than the leaves. Spadix cylindrical, yellow- 

 ish, 2' - 3' long, spreading. 



ORDER 136. LiEMNACE^E. (DUCKWEED FAMILY.) 



Minute aquatic floating plants, with lenticular proliferous stems (fronds), 

 and usually simple roots, pendent from beneath. Flowers monoecious, 

 mostly from a marginal cleft of the stem. Spathe membranaceous, 

 pitcher-shaped, bursting into two unequal lobes, soon vanishing, commonly 

 enclosing two sterile flowers, which are reduced to single slender filaments 

 bearing a 2-celled anther, and a single sessile 1-celled ovary, which forms 

 in fruit a 1-7-seeded utricle. Embryo straight, in the axis of fleshy 

 albumen. 



1. LEMNA, L. DUCKWEED. 



Spathes marginal, 3-flowered. Anthers opening transversely Stigma funnel- 

 form. Ovules erect from the base of the cell, anatropous or half-anatropous. 

 Stems increasing by lateral buds. Roots terminating in a calyptre-like append- 

 age. The flowers of these plants are seldom seen. 



1. L. minor, L. Stems pale, round-obovate, flattened, single or variously 

 clustered ; root single ; ovule solitary, half-anatropous ; seed horizontal. Pools, 

 ditches, &c., Florida, and northward ; common near the coast, and probably 

 intermixed with L. perpusilla, Torr. Stems l"-2" long. 



