bility that it occurs in marshes along the Sabine River in Texas. 



A specimen of Lysichitum americanuin Hult. & St. John in the University of 

 Te.Kas herbarium bears the label "Gregg Co., March 20, 1943, Mrs. C. L. York." 

 This typically far northern species, which was probably under cultivation at this 

 Texas locality, resembles O. aquaticum but differs from it superficially by the 

 more slender peduncle that is distinctly demarcated from the spadix. 



4. Acorus L. Sweetflag. Calamus 

 A genus of 2 species in the Northern Hemisphere. 



1. Acorus Calamus L. Fig. 284. 



Aromatic plants with thick creeping rhizome and ensiform leaves crowded at 

 the base, erect, linear and more or less ensiform, to 2 m. long and 25 mm. wide; 

 scape resembling the leaves; spadix cylindrical, diverging laterally from a tall 

 3-angled scape, the upper and more foliaceous prolongation of the scape may be 

 considered as a kind of open spathe, covered with yellowish-brown perfect flowers, 

 to 1 dm. long and 1 cm. thick at anthesis, to as much as 2 cm. thick at maturity; 

 perianth of 6 short concave segments: stamens 6, the linear filaments thin and 

 flat, with 1 -celled anthers reniform and opening transversely; ovary 2- or 3-celled; 

 fruit obpyramidal, about 4 mm. long. 



Wet places and borders of quiet water, reported (but not seen) from Okla., in 

 n -cen. and n.e. (Marion Co.) Tex.. May-Aug.; from P.E.I., s. to Fla., w. to 

 Mont., Ore. and Tex.; early introd. from Eur. and naturalized. 



Muskrats are known to eat the plants. 



5. Pistia L. Water-lettuce. Water-bonnet 

 A monotypic genus in southern United States and Latin America. 



1. Pistia Stratiotes L. Fig. 287. 



Plants monoecious, floating herbs; leaves clustered on very short branches at 

 the nodes of the rootstock; leaf blades entire, cuneate to obovate-cuneate, to 

 about 25 cm. long, strongly ribbed, dilated upward: spadix adnate to the axillary 

 spathe; spathe about 15 mm. long, pubescent, the upper part ovate; flowers uni- 

 sexual, the pistillate solitary and the staminate above the pistillate; perianth none. 



Streams, lakes and ponds in s. and s.w. Tex. (Fort Bend and Val Verde cos.); 

 spring; from Fla., w. along the coast to Tex., through Latin Am. to S.A. 



Fam. 28. Lemnaceae S. F. Gray Duckweed Family 



Minute green aquatic herbs floating on or below surface of water, often form- 

 ing a solid cover over the surface, occasionally in wet seepage places, much- 

 reduced and simplified in structure, stemless, rootless or with few nonfunctional 

 roots, vascular tissue lacking in many of the species, reproducing chiefly by 

 budding from a single basal pouch or 2 lateral pouches, many successive genera- 

 tions sometimes remaining attached by short stipes: flowers from a saclike spathe 

 in a pouch at the basal margin of the frond or breaking through the surface to 

 one side of the spathe, consisting either of a single stamen or a single pistil, 

 often 2 staminate flowers and 1 pistillate flower to a spathe; fruit a 1- or 2-seeded 

 utricle; seed large, smooth or ribbed. 



A family consisting of 4 well-defined genera and including about 40 species. 



All of the species that comprise this family, especially Lemna minor, are used 

 more or less by wildlife. Many species of duck as well as marsh birds and shore- 

 birds scoop up these tiny plants along with associated minute animal organisms 



563 



