376 
Leaves much reduced above and bract-like. 
4. P. ramossissimum Michx. Erect or ascending, 6 to 12 dm. high, yellowish- 
green: leaves lanceolate to linear, 2.5 to 6 cm. long, acute: flowers and achenes as 
in the last, but sepals more frequently 6, the stamens 3 to 6, and the achene mostly 
smooth and shining.—Sandy shores and banks of streams, extending from Texas to 
the far north and west. 
5. P. tenue Michx. Stem slender, angled, erect (1.5 to 4.5 dm. high), slightly 
scabrous at the nodes: leaves narrowly linear to lanceolate (2.5 to 5 cm. long), 
3-nerved, acute at each end and often cuspidate, the margins somewhat scabrous 
and at length revolute: flowers often solitary, nearly sessile: stamens 8: achene 
ovate, included, black and shinizg.—From El Paso to central Texas. 
6. P. camporum Meisn. Stem round, erect or ascending, 6 to 9 dm, high: leaves 
deciduous, linear to oblong, usually short: pedicels slender, exserted from the 
searious sheaths: stamens 8.—From the upper Pecos to the lower Rio Grande. 
** Flowers in dense spikes, with small scarious bracts: leaves not jointed on the petiole ; 
sheatha cylindrical, truncate, entire, naked or ciliate-fringed or margined: calyx colored, 
5-parted, appressed to the fruit: stamens 4 to 8; filaments filiform. 
, ? d 
+ Sheaths and bracts not ciliate or fringed : sepals not punctate : styles 2-cleft (often 3-cleft 
in No, 11). 
7. P. lapathifolium L. Annual, branching, 3 to 12 dm, high, glabrous or the ped- 
uncles often minutely glandular: leaves lanceolate, attenuate upward from near the 
cuneate base and acuminate, somewhat seabrous with short appressed hairs on the 
midrib and margin, or rarely floceose-tomentose beneath; sheaths and bracts rarely 
somewhat ciliolate: spikes oblong to linear (1.5 to 5 cm. long), dense, erect or 
nearly so: flowers white or pale rose-color: stamens 6: achene ovate, rarely 2 mm. 
broad.—Wet places along the Pecos and the Rio Grande. A very variable species, 
Var. INCARNATUM Watson has leaves often large (1.5 to3 dm. long, 2.5 to8 cm. broad), 
and nodding spikes more slender and elongated (5 to 10 cm, long).—Central and 
northern Texas. 
8. P. Pennsylvanicum L. A similar species, but the branches above and espe- 
cially the peduncles beset with stipitate glands; flowers larger and often bright 
rose-color, in short erect spikes, often on exserted pedicels: stamens usually &: 
achene nearly orbicular, over 2 mm, broad,—Moist soils, from the upper Pecos and 
the lower Rio Grande to central Texas. 
9, P. amphibium L. Perennial, aquatic or rooting in the mud, stout and gla- 
brous or nearly so, not branching above the rooting base: leaves usually floating, 
thick, smooth and shining above, mostly long-petioled, elliptical to oblong or some- 
times lanceolate, acutish, cuneate or cordate at base (5 to 12.5 em. long): spikes ter- 
minal, dense, ovate or oblong (1 to 2.5 em, long): flowers bright rose color (3 to 6 
mm. long): the 5 stamens and style exserted.—From the upper Pecos to the lower 
Rio Grande. 
10. P. emersum (Michx.) Britton. Perennial, in muddy or dry places, decumbent 
or suberect, scabrous with short appressed or glandular hairs: leaves thinner, rather 
broadly lanceolate, narrowly acuminate (10 to 18cm. long): spikes more elongated 
(2.5 to 7.5 em. long), often in pairs: flowers and fruit nearly as in the last. (P. amphi- 
bium, var. emersum Michx. P. Muhklenbergii Watson.)—Western Texas, 
11. P. densiflorum Meisn. Stem stout, 6 to 12 dm. high, branching above: leaves 
lanceolate or oblong-lanceolate (15 to 25 em. long), tapering at the summit, but rather 
obtuse, rough on the margins and veins: spikes racemed or somewhat panicled, 
linear (5 to 10 em. long), erect, densely white-flowered, the peduncles minutely glan- 
dular: bracts obliquely truncate: stamens usually 6: achene round-ovate, black 
and shining, with convex sides, (Incl, most of P. glabrum of authors, not Willd, )— 
/xtending from the Gulf States through Texas to tropical America, 
