NAIADACE.fi. (PONDWEED FAMILY.) 557 



ORDER 126. NAIAD ACE^E. (PONDWEED FAMILY.) 



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

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

 and Jlowers perfect or unisexual, often spathaceous, with perianth of 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. Juneaginese. Marsh plants, with terete bladeless 

 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, 



in a spike-like raceme terminating a jointless scape. 



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



loose raceme upon a leafy stem. 



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

 ovaries solitary or distinct, 1-ovuled. 



t- 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 long-exserted, without perianth. 



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



*- H- Flowers monoecious or dioecious, axillary, naked, inonandrous ; leaves opposite (alter- 

 nate in n. 6). 



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



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



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 rpets, three, and y\wxtv, point, from the three points of 

 the ripe fruit in n. 1 when dehiscent.) 



# Fruit of 3 carpets. 



1. T. paliistris, 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, awl-pointed at base. Marshes, western 

 N. Y. to 111., Minn., and westward. Aug. (En., 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-ahore, Md. to Ela. (S. Am., etc.) 



