144 LEMNACEAE 



Fronds long-stalked, mostly submerged, forming large masses 1. L. trisulca. 



Fronds short-stalked or sessile, floating on the surface. 



Frond pale and usually strongly gibbous beneath. 2. L. gibba. 



Fronds green or purplish, not gibbous beneath. 



Frond oblong-obovate. indistinctly 3-nerved. 3. L. minor. 



Frond oblong or elliptical, indistinctly 1-nerved or nerveless. 



Frond unsymmetrical, without papules. 4. L. cyclostasa. 



Frond symmetrical, with a row of papules along the midvein. 5. L. minima. 



1. L. trisulca L. Fronds usually submerged, seldom floating, usually 

 several generations attached together, oblong to oblong-lanceolate, slightly un- 

 symmetrical and falcate, dentate towards the upper end, 5-10 mm. long, 2-3 mm. 

 wide. In springs and running water: N.S. N.J. Tex. -Calif. B.C.; Old 

 World and Australia. Plain Mont. Jl-Au. 



2. L. gibba L. Fronds solitary or 2-4 in a group, orbicular to obovate, 2-5 

 mm. long and 2-4 mm. wide, thick, convex and slightly keeled above, with large 

 air-cavities in the gibbous portion, unsymmetrical, 3-5-nerved. In ponds: Neb. 

 Tex. Ariz. 'Calif.; Mex.; Old World and Australia. Plain Subalp. 



3. L. minor L. Fronds solitary or a few together, round to oval, sym- 

 metrical, thickish, convex on both sides, sometimes slightly keeled above and 

 with a row of papules along the midrib. In stagnant water and slow streams: 

 Lab. Fla. Calif. Alaska; Mex.; Old World and Australia. Plain -Mont. 



4. L. cyclostasa (Ell.) Chev. Frond solitary or 2-8 in a group, oblong to 

 obovate-oblong, usually somewhat falcate, 2.5-4.5 mm. long, 1-1.5 mm. wide, 

 usually unsymmetrical at the base. L. valdiuiana Philippi. In pools and streams : 

 Mass. Fla. Calif. Ida.; Mex. S. Am. Plain -Submont. 



5. L. minima Philippi. Fronds solitary or in groups of 2-4, oblong or 

 elliptical, symmetrical, 1.5-4 mm. long, 1-2.75 mm. wide, both surfaces convex 

 or the lower flat, with a thin margin around the frond. In pools: Ga. -Kans. 

 Wyo. Calif.; Mex. S. Am. Plain -Submont. 



2. SPIRODELA Schleiden. LARGER DUCKWEED. 



Frond disk-like, several-nerved. Stipe attached peltately to the frond back 

 of and under the basal margin. Rootlets several, each with a solitary fibro- 

 vascular bundle. Anthers dehiscent longitudinally. 



1. S. polyrhiza (L.) Schleiden. Frond solitary or in colonies of 2-5, round- 

 ish obovate, flat on both sides, green above, generally purplish beneath, 5-15- 

 nerved, 2.5-4.5 mm. wide and 2.5-8 mm. long; rootlets 4-16. In pools and 

 ponds: N.S. B.C. Fla. Mex.; Old World and S. Am. Plain. 



Family 16. COMMELINACEAE. SPIDERWORT FAMILY. 



Somewhat succulent herbs, with fibrous or tuberous-thickened roots and 

 alternate leaves sheathing at the base. Flowers perfect, subtended by leaf- 

 like sheathing bracts. Sepals 3, herbaceous. Corolla regular or irregular, 

 with 3, usually showy, colored petals. Stamens 6 or 5, sometimes 2 or 3 

 of these sterile. Gynoecium of 2 or 3 united carpels; ovary superior, 2- or 

 3-celled; styles united. Fruit a loculicidal capsule. 



Petals all alike; perfect stamens 6; bracts leaf-like. 1. TRADESCANTIA . 



Petals unlike in shape and size; perfect stamens 3 or 2; bracts spathe-like. 



2. COMMELINA. 



1. TRADESCANTIA (Rupp.) L. SPIDERWORT. 



Caulescent perennials, with alternate narrow leaves. Cymes umbel-like, 

 terminal, subtended by usually 2 bracts, similar to the leaves. Sepals 3, nearly 

 equal, distinct. Petals 3, showy, blue, rose-color or white, sessile, similar and 

 equal, delicate. Stamens 6, all perfect; filaments filiform, in ours long-hairy. 

 Capsule loculicidal, 3-valved. Seeds 3-6, more or less sculptured. 



Sepals glandular-pilose; petals about 15 mm. long; capsule decidedly ellipsoid. 



Bracts broader than the leaves, strongly gibbous at the base; stem 2-3 dm. high, 

 usually simple; pod densely glandular. 1. T. bracteata. 



