EL A TIN A CEA E. 629 



4. TRIADENUM Raf. [ELODEA Pursh.] 



Perennial marsh herbs, with entire oblong oval or ovate leaves, and pink or 

 greenish purple flowers in terminal cymes, or also axillary. Calyx of 5 equal per- 

 sistent sepals. Petals 5, not contorted. Stamens 9, or sometimes more, in 3 sets, 

 the sets alternating with 3 large hypogynous glands. Ovary 3-celled; styles 3. 

 Capsule oblong-conic, much longer than the sepals. [Greek, three glands.] Two 

 species, natives of E. N. Am. 



Leaves sessile; flower-clusters peduncled. 1. T. Virginicum. 



Leaves short-petioled ; flower-clusters nearly sessile. 2. T. petiolatum. 



1. Triadenum Virginicum (L.) Raf. Marsh St. John's-wort. (I. F. f. 

 2464.) Nearly simple, 3-5 dm. high. Leaves sessile or cordate-clasping, ovate or 

 oblong, 2-6 cm. long, very obtuse, sometimes emarginate, glaucous beneath, black- 

 dotted; flowers 12-16 mm. broad, in leafy clusters; sepals acute, shorter than the 

 straight petals; stamens 9 or more, united in 3 sets; styles 3, distinct; capsule ob- 

 long, 8-10 mm. long, acute, red-purple. In swamps, Lab. to Fla., Man., Neb. and 

 La. July-Sept. 



2. Triadenum petiolatum (Walt.) Britton. Larger Marsh St. John's- 

 wort. (I. F. f. 2465.) Similar to the preceding, but often more branched and 

 taller; leaves generally longer, petioled, or the upper sessile, not clasping, pale 

 beneath; flower-clusters sessile or very short peduncled. In swamps, N. J. and 

 Md. to Fla., Ark. and La. July- Aug. 



Family 3. ELATINACEAE Lindl. 



Water-wort Family. 



Low herbs, sometimes woody in tropical regions, with opposite or 

 verticillate stipulate leaves, and small axillary regular perfect flowers. 

 Sepals 2-5, imbricated. Petals the same number, hypogynous. Stamens 

 the same number or twice as many. Ovary 2-5-celled ; styles 2-5, stig- 

 matic at the apex ; ovules 00 , anatropous. Capsule with septicidal dehis- 

 cence. Placentae central. Seed- coat crustaceous, rugose or ribbed. 

 About 25 species, of wide distribution. 



Flowers 2-4-merous; glabrous aquatic or creeping herbs. 1. Elatine. 



Flowers mainly 5-merous ; pubescent ascending or diffuse herbs. 2. Bergia. 



1. ELATINE L. 



Small glabrous or glabrate aquatic or creeping herbs, with minute mainly soli- 

 tary flowers. Sepals 2-4, persistent, membranous, not ribbed. Styles or stigmas 

 2-4. Pod membranous, globose, 2-4-valved. Seeds oo , straight, or slightly curved, 

 striate longitudinally and transversely. [Greek, fir-like, with reference to the leaves.] 

 About 9 species, of temperate and warm regions. In addition to the following, 

 another occurs in Cal. 



Petals and stamens 2 ; seeds distinctly sculptured. 



Leaves obovate ; seeds with 9-10 longitudinal and 20-30 transverse striae. 



1. E. Americana. 

 Leaves oblong or oval ; seeds with 6-7 longitudinal and 10-12 transverse striae. 



2. E. brachysperma. 

 Petals and stamens mostly 3 ; seeds little sculptured. 3. E. triandra. 



1. Elatine Americana (Pursh) Am. Water-wort. Mud-purslane. (I. F. 

 f. 2466.) Tufted, aquatic or terrestrial, 1-4 cm. long. Leaves obtuse, 2-6 mm. 

 long, 2 mm. wide or less; flowers sessile, minute, rarely opening in the submerged 

 forms; sepals, petals, stamens and stigmas 2 (rarely 3 in the terrestrial forms); 

 capsule globose, nearly 1 mm. in diameter; seeds 0.5-1 mm. long, slightly curved. 

 Margins of ponds and slow streams, Me. and Ont. to Va., Mo. and Tex. Also in 

 Colo, and Ore. Summer. 



2. Elatine brachysperma A. Gray. Short-seeded Water-wort. (I. F. f. 

 2467.) Terrestrial or sometimes submerged, spreading, tufted. 2-5 cm. long. 

 Leaves oblong, oval or lanceolate, narrowed at the base, 4-6 mm. long, about 



