456 
flowers 6 mm. broad: stamens 9: style much shorter than the ovary: achenes beak- 
less, obtusely few-ribbed.—In mud, extending from the Atlantic States to Texas, 
2. E. rostratus Engelm. Scape erect (1 to 6 dm. high), longer than the leaves: 
leaves broadly ovate, cordate or truncate at base, obtuse, 6 to 12 cm. long: umbels 
proliferous, in a branched panicle: flowers 10 mm. broad: stamens 12: styles longer 
than the ovary: achenes beaked, acutely many-ribbed.—Western Texas. 
3. B. radicans Engelm. Stems or scapes prostrate, creeping (6 to 12 dm. long), 
proliferous, bearing many whorls of flowers: leaves truncately broadly cordate, 
obtuse (5 to 20 em, broad), long-petioled: flowers 12 to 18 mm. broad: stamens about 
21: styles shorter than the ovary: achenes short-beaked, the keeled back denticu- 
late.—Central and western Texas. 
NAIADACEZA. (POND-WEED FAMILY.) 
Immersed aquatic herbs, with leafy-jointed stems, flat leaves stipu- 
lar or sheathing at base, perfect: or unisexual (often spathaceous) flow- 
ers, with or without a perianth, 1 to 4 stamens with extrorse anthers, 
and solitary or distinct one-ovuled ovaries. 
* Flowers perfect: leaves alternate. 
1. Potamogeton. Spike peduncled: sepals 4: stamens 4. 
2. Ruppia. Flowers on a spadix, without a perianth: stamens 2, with 2 distinct 
cells. 
* * Flowers monecious or diwcious, monandrous: leaves opposite. — 
38. Zannichellia. Moneecious: pistils 2 to 5, from a cup-shaped involucre. 
4. Naias. Diccious: pistil solitary, naked. 
1. POTAMOGETON L. (POND-WEED.) 
Brackish or fresh-water herbs, with slender branching stems, 
2-ranked alternate (or imperfectly opposite) leaves, membranaceous 
sheathing stipules, spike of perfect flowers sheathed by stipules in the 
bud, 4 rounded sepals with as many opposite stamens (anthers nearly 
sessile), 4 ovaries, subsessile stigmas, and the ovate compressed drupe- 
like fruit with a crustaceous nutlet within. 
* Leaves of two sorts: floating ones more or less coriaceous, with a dilated petioled blade, 
different in form from the thinner submersed ones. 
+ Submersed leaves reduced to narrowly grass-like or filiform sessile phyllodia. 
1. P.natans L. Stem rather stout, simple or sparingly branched: floating leaves 
long-petioled, elliptical or ovate, somewhat cordate at base, obtuse, 21 to 29-nerved ; 
upper submersed leaves lanceolate, the lower (later in the season) very slender; 
stipules free, the upper very long and acute: peduncle about the thickness of the 
stem: spike 2.5 to 5 cm. long, emersed: fruit obliquely obovate, acute, fleshy turgid: 
nutlet with a small deep impression in the middle.— Waters of the Limpia. 
2. P. hybridus Michx. Stems slender, much branched: floating leaves oval to 
lance-oblong, large, longer than the filiform petioles, with 5 to 7 deeply impressed 
nerves; submersed leaves very numerous, almost setaceous, 2.5 to 7 cm. long; stipules 
obtuse, adnate to the base of the leaf: emersed spikes 10 to 18 cm. long; the sub- 
mersed ones 1 to 4-flowered, their peduncles frequently recurved: fruit: minute, 
about 8-toothed on the margin.—Shallow stagnant waters on the prairies of the 
Guadalupe River. 
