28 ALISMACEAE 



in verticils of 3's near the top of the scapes, pedicelled, thestaminate uppermost. 

 Sepals and petals 3; the latter large, white. Stamens numerous, inserted on the 

 convex receptacle; anthers 2-celled, dehiscent by lateral slits. Pistillate flowers 

 with nimierous pistils. Achenes densely aggregated in globular heads, fiat and 

 often wing-margined. 



Leaf-blades usually ^vithout basal lobes; beak borne below the top of the achenes. 



1. S. graminea. 

 Leaf-blades or some of them sagittate or hastate, with basal lobes; beak borne at the top 

 of the achenes. 

 Beak short, erect; bracts lanceolate or linear-lanceolate. 



Basal lobes of the leaves acute or acuminate. 2. S. cuneata. 



Basal lobes of the leaves rounded or obtuse. 3. S. hebeliloba. 



Beak of the achenes horizontal. 



Beak short; basal lobes of the leaves at least twice as long as the terminal one; 

 bracts lanceolate. 4. S. longiloba. 



Beak long; basal lobes of the leaves usually shorter than the terminal one: bracts 

 ovate. 5. S. latifolia. 



1. S. graminea Michx, Plant emersed or submerged, 1-6 dm. high; phyl- 

 loids if present, flattened, linear-lanceolate, acute, 8-30 cm. long, 1-2 cm. wide; 

 leaf-blades lanceolate to ovate-eUiptical, acute at both ends, or very rarelj' trun- 

 cate, with short divaricate lobes at the base, 5-15 cm. long, 3-5-ribbed; bracts 

 ovate, acute, 3-5 mm. long, connate to the middle; fruiting heads 5-10 mm. in 

 diameter; achenes 1.5 mm. long, dorsally crested and obhquely one-ribbed on the 

 sides. In shallow ponds and marshes: Newf. — Fla. — Tex. — -Sask. Plain. 



2. S. cuneata Sheld, A rather weak plant growing in mud or water, glab- 

 rous, 2-4 dm. high; leaves when emersed sagittate; petiole rather stout, usually 

 curving outwards; blade 6-18 cm, long; basal lobes narrow, lanceolate, some- 

 what divergent; blades in deep water less developed, sometimes not lobed, float- 

 ing; bracts lanceolate or linear-lanceolate, acute, 8-20 mm. long, scarious-mar- 



'gined; fruiting heads 10-15 mm. in diameter; achenes 2 mm. long, winged on 

 both margins. S. arifolia'Nutt. In mud and shallow water: Me. — N.D, — Conn. 

 —Kans.—N.M.— Calif.— B.C. PlainSuhmonl. 



3. S. hebetiloba A. Nels. A rather stout plant, 2-5 dm. high, monoecious; 

 leaf-blades sagittate, 8-14 cm. long, subacute; bracts linear-lanceolate, 15-20 

 mm. long, subscarious; corolla about 2 cm. in diameter; fruiting heads 10-15 

 mm. in diameter; achenes about 2 mm. long, winged on both margins and the 

 summit. In a bog, formed from warm-spring: Laramie Co., Wyo. Submont. 



4. S. longiloba Engebn, A monoecious, slender, erect perennial, 3-5 dm. 

 high; leaf -blades sagittate; basal lobes linear-lanceolate, acuminate; fruiting heads 

 10-12 mm. in diameter; achenes 2 mm. long, narrowly winged on both margins; 

 beak lateral. In shallow ponds: Neb. — Colo. — Tex. — Sonora. Plain — Son. 



5. S. latifolia Willd. A rather stout plant, monoecious, 3-6 dm. high; 

 with the lower verticils fertile, or rarely dioecious, 3-6 dm. high; leaf -blades 

 sagittate, 15-40 cm. long, very variable, glabrous; lobes from broadly ovate to 

 linear-lanceolate [v, anguRtiJolia], acute or acuminate; bracts ovate, acute, 1-3 cm. 

 long; flowers 3-4 cm. wide; fruiting heads 15-30 mm, in diameter; achenes about 

 3 mm. long, winged on both margins; beak triangular-lanceolate, acuminate, making 

 almost a right angle to the achenes. Shallow water: N.B, — Fla. — CaUf, — B.C. 

 Mex, and C. Am, Son. — Plain — Mont. Je-S. 



Family II. ELODEACEAE. Water- weed F.\mily. 



Submersed or floating water plants. Leaves in ours opposite or whorled. 

 Plants monoecious, dioecious or polygamous. Flowers enclosed in a spathe 

 of 1-3, usually united bracts. Hypanthium in the pistillate flowers well de- 

 veloped, tubular, in the staminate flowers often shorter or obsolete. Peri- 

 anth regular or nearly so. Sepals 3. Petals 3, or wanting. Stamens 3-9; 

 filaments short, often monadelphous. Pistil single, compound. Ovary I- 

 cclled with 2-6, usually 3, parietal placentae. Ovules numerous. Fruit 

 indehiscent, maturing under water. 



