139. BURMANNIACEAE 293 



3-4.5 mm broad; rhizome mosUy 5-8 mm thick (when dry), 

 simjile, or rarely branched; thickets or open woods, common. 



May-July. [D. paniculata Michx.] D. villosa L. 



1. Petioles puberulent at the insertion of the blade; mature capsules 

 2.5-3 cm long; lower leaves in whorls of 4-9 (usually 6) ; lower 

 surface of blades glabrous or puberulent, glaucous or green; 

 seeds (exclusive of the wing) 5-6.5 mm broad; rhizome stout, 

 irregularly knotted, 1-1.5 cm thick; woods, s. 111. May-June 

 D. quaterjiata (Walt.) Gmel. 



138. Hydrocharitaceae Aschers. — Frogbit Family 



1. Leaves cordate, petioled 1. Limnobium 



1. Leaves neither cordate nor petioled. 



2. Leaves basal, ribbon-like, elongated, floating 2. Vallisneria 



2. Leaves small, whorled or opposite, sessile, pellucid, 1-veined; stems elon- 

 gated, leafy, floating 3. Elodea 



1 . Limnobium Rich. — Frogbit 



L. spongia (Bosc) Steud. Sponge-plant. Shallow water or mud, 

 rare; Alexander and Union counties. June-Aug. 



2. Vallisneria L. — Tapegrass 



V. americana Michx. "Wild Celery." Ponds and slow streams in 

 the northern half of the state. July-Aug. 



3. Elodea Michx. — W^aterweed 

 {Anacharis Rich.) 



1. Leaves three in each whorl, 1-2 cm long; flowers 3-6 mm in di- 

 ameter, solitary in the spathe. 

 2. Leaves elliptical or oblong, obtusish, 1.5-4 mm wide; slow 

 streams, widely distributed. July-Aug. Canadian Water- 



w^eed E. canadensis Michx. 



2. Leaves linear, acute, niostly 1-1.5 mm wide; ponds and slow 

 streams, apparently more common in 111. than the preceding 

 species. July-Aug. Common Waterweed. [E. nuttallii 



(Planch.) St. John] E. occidentalis (Pursh) St. John 



1 . Leaves six in each whorl, 2-4 cm long, 3-5 mm wide, the stem 

 densely leafy; flowers 1.5-2 cm in diameter, usually 3 in a 

 spathe; used in aquaria and rarely found as an escape from 

 cult.; introd. from S. Am. Brazilian Waterweed. .../s. dcnsa Planch. 



139. Burmanniaceae Blimie — Burmannia Family 



1. Thismia GrifT. 



T. americana N.E.PfeifT. "Chicago, 111., in open j^rairie," Norma 

 E. Pfeiffer; known only from the original collection; type, herb. 

 Chicago Nat. Hist. Mus. ; isotype, herb. Univ. of 111. Discovered in 

 Aug. 1912, now almost certainly extinct. 



