442 LEMNACE^. (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-pctioled leaves, aud a yellow erect spadix terminating the club- 

 shaped scape. 



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

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

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

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

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



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- 

 cclled, 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. LEMNACE^. (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-cellcd 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. 



Spathcs marginal, 3-flowcred. Anthers opening transversely Stigma funnel- 

 form. Ovules erect from the base of the cell, anatroj)Ous or lialf-anatropous. — 

 Stems increasing by lateral buds. Roots terminating in a caly])iri-like append- 

 age. — The flowers of these plants arc seldom seen. 



1. L. minor, L. Stems pale, roundobovate. flattened, single or variou-ly 

 clu-stored ; 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 — Slcnia l"-2" long. 



