468 NAIADACE^E. (POXDWEED FAMILY.) 



1. TYPHA, Tourn. CAT-TAIL. 



Flowers densely crowded on a long cylindrical terminal spadix, enveloped 

 in copious pappus-like hairs; the sterile ones sessile on the upper part of the 

 spadix, the fertile on slender stalks. Style filiform : stigma lateral. Stems 

 straight, from a thick rhizoma, clothed below with the sheathing bases of the 

 elongated linear leaves. Spathes bract-like and deciduous, or none. 



1. T. latifolia, L. Stem terete, jointed below ; leaves nearly as long as 

 the stem, erect, flat, reticulated and somewhat glaucous ; sterile and fertile 

 portions of the spadix contiguous, cylindrical. Margins of ponds and rivers, 

 Florida, and northward. July- August. Stem 4 -6 high, scape-like 

 above. Leaves about 1' wide. Spadix about 1 long. T. angustifolia, L., 

 if found within our limits, may be known by narrower leaves which are chan- 

 nelled near the base, and by the interval which separates the sterile and fer- 

 tile portions of the spadix. 



2. SPARGANIUM, L. BUR-REED. 



Flowers densely crowded in globular heads, surrounded by several scales 

 like a calvx ; the upper heads sterile, naked, the lower fertile and commonly 

 bracted. Ovarv sessile, pointed by the short persistent style. Stigma lateral. 

 Marsh or aquatic plants, with erect stems, and long strap-shaped sessile 

 leaves, the lowest sheathing. Heads of flowers scattered. 



1. S. simplex, Huds. Leaves flat, obtuse, the upper concave and clasp- 

 ing, the lower sheathing ; heads scattered, the lowest larger and pistillate, the 

 others staminate ; scales wedge-shaped ; stigma subulate, simple. Ponds and 

 ditches. July. Stem 1 - 2 high. Heads 6" - 10" broad. 



ORDER 140. NAIADACEJE. (POXDWEED FAMILY.) 



Aquatic herbs, with slender jointed leafy immersed stems, and per- 

 fect or monoecious or dioecious flowers, destitute of floral envelopes, or 

 with scale-like sepals. Stamens 1-4: anthers 1-4-celled. Ovary 1- 

 celled, forming a 1-seeded achenium in fruit. Stigmas 1-4. Seed 

 without albumen. Embryo straight, curved, or coiled. Leaves 

 sheathing, or with sheathing stipules. Flowers commonly enclosed 

 in a spathe. 



Synopsis. 



* Flowers monoecious or dioecious. 



1. NAIAS. Stigmas 2 -4. Flowers naked. Leaves opposite or whorled. 



2. ZOSTERA. Stigmas 2. Flowers enclosed in a spathe. Leaves alternate. 



3. ZANNICHELLJA.. Stigma single, peltate. Ovaries 4, from a cup-like involucre. 



4. THALASSIA. Flowers dioecious. Sepals 3 Anthers 9, sessile. 



* * Flowers perfect. 



5. RUPPIA. Fruit long-peduncled, umbellate. Calyx and corolla none. 



6. POTAMOGETON. Fruit sessile, spiked. Calyx 4-leaved. 



