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 nimierous, inserted on the 

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

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

 often wing-margined. 



Leaf-blades usually without 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. cuneaia. 



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



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-elliptical, acute at both ends, or verj' rarely 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: fniiting heads 5-10 mm. in 

 diameter; achenes 1.5 mm. long, dorsally crested and obhquclv 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 

 curvmg outwards; blade &-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.— CaUf.— B.C. PlainSubmonL 



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 Engelm, 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. 



onoecious, 3-6 

 3-6 dm, hiffh: 



sagittate, 15-4U cm. long, very variable, glabrous; lobes from broadly ovate to 

 Imear-lanceolate [v. angii.stifolia], acute or acuminate; bracts ovate, acute, 1-3 cm. 

 long; flowers 3-4 cm. wide; fruitmg 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 —Calif.— B.C. 

 Mex. and C. Am. Son.— Plain— MonL Je-S 



Family 11. ELODEACEAE. Wateh-weed Family. 



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 1- 

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

 indehiscent, maturing under water. 



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