NAIADACE^E. (PONDWEED FAMILY.) 557 



ORDER 126. XAIADACE-E. (POXDWEBD FAMILY.) 



Marsh or mostly immersed aquatic herbs, with steins jointed and leafy or 

 (in Triglochiu) naked and scape-like, leaves sheathing at base or stipulate, 

 and flowers perfect or unisexual, often spathaceous, with perianth 0/4 or 6 

 herbaceous distinct valvate segments, or membranous and tubular or cup- 

 shaped, or none. Stamens 1, 2, 4 or 6, with extrorse anthers. Ovaries 

 1-6, distinct or more or less coherent, 1 -celled, usually 1-ovuled, in fruit 

 follicular or capsular or an indehiscent berry or utricle. 



SUBORDER I. Juncagineae. Marsh plants, with terete bladelcss 

 leaves ; flowers perfect, spicate or racemose, with herbaceous 6- (rarely 

 3-) lobed perianth ; carpels 3 or 6, more or less united, separating at 

 maturity. Seeds anatropous ; embryo straight. 



1. Triglochin. Ovaries 3-6, united until maturity. Leaves radical. Flowers bractless, 



iu a spike-like raceme terminating a joiatless scape. 



2. Scheuchzeria. Ovaries 3, nearly distinct, at length divergent. Flowers bracteate in a 



louse raceme upon a leafy stem. 



SUBORDER II. Naiadeje. Immersed aquatics, with flat leaves; 

 ovaries solitary or distinct, 1-ovuled. 



i- Flowers perfect, spiked or clustered ; anthers 4 or 2, sessile ; leaves alternate. 



3. Potamogeton. Spike peduncled. Sepals 4, herbaceous. Anthers 4. Ovaries 4, sessile. 



4. Ruppia* Flowers on an enclosed spadix, at length loug-exserted, without perianth. 



Anther-cells 4, distinct. Ovaries 4, becoming stipitate. 



-- -t- Flowers monoecious or dioecious, axillary, naked, inoiiandrous ; leaves opposite, (alter- 

 nate in n. 6). 



5. Zannichellia, Monoecious. Pistils (2 - 0) from a cup-shaped involucre or sheath. 



6. Zostera. Pistils and stamens alternate in 2 vertical rows on the inner side of a leaf-like 



enclosed spadix. Stigmas 2, linear. Stem creeping. 



7. Naias. Dioecious ; pistil solitary, naked. Stamen enclosed in a membranous spathe. 



Stems floating, with opposite or ternate leaves. 



1. TRIGLOCHIN, L. ARROW-GRASS. 



Sepals and petals nearly alike (greenish), ovate, concave, deciduous. Sta- 

 mens 3 - 6 ; anthers oval, on very short filaments. Pistils united into a 3 - 6- 

 celled compound ovary ; stigmas sessile ; ovules solitary. Capsule splitting 

 when ripe into 3-6 carpels, which separate from a persistent central axis. 

 Perennials, with rush-like, fleshy leaves, below sheathing the base of the wand- 

 like naked and jointless scape. Flowers small, in a spiked raceme, bractless. 

 (Name composed of Tpei 1 ?, three, and yAooxi-v, point, from the three points of 

 the ripe fruit in n. 1 when dehiscent.) 



* Fruit of 3 carpels. 



1. T. palustris, L. Scape (6-18' high) and leaves slender; sepals and 

 stamens 6 ; fruit linear-club-shaped; carpels when ripe separating from below 

 upward, leaving a triangular axis, aid-pointed at base. Marshes, western 

 N. Y. to 111., Minn., and westward. Aug. (Eu., Asia, etc.) 



2. T. stri&ta, Ruiz & Pav. Scape (6-12' high) and leaves slender; flow- 

 ers very small; sepals and stamens 3; fruit globose-triangular, or when dry 

 3-lobed. (T. triandra, Michx.) Sea-shore, Md. to Fla. (S. Am., etc.) 



