(Last Modified On 10/16/2012)
(Last Modified On 10/16/2012)
Syst. Nat. ed. 10. 2:855. 1759.
Spikelets plano-convex, solitary or in pairs, arranged in two rows on one side of a narrow wingless to broadly winged rachis, the back of the fruit turned toward the rachis; first glume wanting or present on some, occasionally on all of the spikelets; second glume and sterile lemma equal, covering the fruit, or the glume a little shorter, rarely wanting; fruit indurate, usually pale, sometimes dark brown, smooth and shining or minutely striate, the margins of the lemma inrolled, en- closing the palea.
Annuals or perennials with one to many racemes, these solitary, paired, or racemose at the summit of the main culm and branches.
a. Inflorescence feathery, composed of numerous, very slender, drooping racemes, crowded on a short axis --- 39. P. SACCHAROIDES
aa. Inflorescence not feathery, the racemes, if hairy, not long, slender, and drooping. b. Rachis winged, with broad membranaceous margins, or if narrowly winged, the spikelets conspicuously fringed with long hairs.
c. Plants terrestrial; spikelets conspicuously silky or fringed with long hairs.
d. Spikelets 2.5-3.2 mm. long; second glume wingless; sterile lemma inconspicuously fringed.
e. Racemes solitary or sometimes paired, the rachis 5-7 mm. wide; culms simple -----1. P. STELLATUM
ee. Racemes 2-7, sometimes solitaryon the branches, never paired, the rachis 2-4 mm. wide; culms usually branching.
f. Blades 2-3.5 mm. wide, flat or becoming involute; racemes 1-6 cm. long, the rachis 3-4 mm. wide; culms slender, erect - -- 2. P. HETEROTRICHON
ff. Blades 6-15 mm. wide, flat; racemes 5-10 cm. long, the rachis 2-3 mm. wide; culms relatively coarse, decumbent at the somewhat woody base - 3. P. HUMBOLDTIANUM
dd. Spikelets 4.5-6 mm. long; second glume broadly winged; sterile lemma fringed with long hairs.
e. Rachis narrower than the spikelets; glume cordate at base; fruit ciliate ----- ---- 4. P. PECTINATUM
ee. Rachis wider than the spikelets; glume not cordate at the base; fruit glabrous - - _ - __ 5. P. CONTRACTUM
cc. Plants aquatic; spikelets glabrous. d. Second glume well developed; spikelets 1.4-2 mm. long, elliptic, acute, in two rows, numerous on each raceme - 6. P. REPENS
dd. Second glume wanting; spikelets 2.3-2.5 mm. long, oblong, obtuse, appearing as if in a single row, relatively few on each raceme _ - _ ---7. P. CANDIDUM
bb. Rachis wingless, or if narrowly winged, the spikelets not conspicu- ously silky or fringed with long hairs.
c. Racemes 2, conjugate or nearly so at the summit of the culm, rarely a third one a short distance below. d. Plants extensively stoloniferous.
e. Spikelets 1.4-2.2 mm. long, ovate, sparsely long-ciliate around the margins -----26. P. CONJUGATUM
ee. Spikelets 3-4.5 mm. long, glabrous. Sea-coast plants - 8. P. VAGINATUM
dd. Plants cespitose or rhizomatous, but not stoloniferous.
e. Plants perennial; spikelets 2 mm. long or more. f. Spikelets 2-3.8 mm. long, ovate to obovate, or, if elliptic, pubescent.
g. Rhizomes stout, horizontal, forming a tough sod; spike- lets glabrous.
h. Spikelets 2.5-3.8 mm. long, ovate to obovate, smooth and shining ---- 9. P. NOTATUM
hh. Spikelets 2-2.5 mm. long, oval, less shining than the preceding _ ----- 1 0. P. MINUS
gg. Rhizomes short; spikelets pubescent - - _ 11. P. SUBCILIATUM ff. Spikelets 4-4.5 mm. long, elliptic, glabrous, with a short tuft of hairs on either side at the base. Base of plant usually covered with old shredded sheaths --- 12. P. LINEARE
ee. Plants annual; spikelets 1.1-1.5 mm. long.
f. Spikelets subhemispheric, solitary, beaded with globular hairs, rarely glabrous - -- 18. P. MULTICAULE
ff. Spikelets elliptic or obovate, paired, pubescent with capitate hairs - - _ _ _ - _ ----- 19. P. CLAVULIFERUM
cc. Racemes 1-many, racemose or fascicled on the axis, not conjugate. d. Second glume wanting. Pedicels bearing stiff hairs at least as long as the spikelet _ - _ ---37. P. GARDNERIANUM
dd. Second glume well developed.
e. First glume present on at least one of a pair of spikelets (see also P. fasciculatum, a coarse aquatic).
f. Plants decumbent, creeping; spikelets not more than 2 mm. long.
g. First glume about equally developed on all spikelets 14. P. DECUMBENS
gg. First glume wanting, or occasionally developed, especially on the secondary spikelet _ - _ - _ 15. P. NUTANS
ff. Plants erect; spikelets 2.6-3 mm. long - _ 16. P. PILOSUM
ee. First glume wanting, or occasionally developed on some of the spikelets.
f. Racemes terminal and axillary, the axillary sometimes hid- den in the sheaths. g. Culms decumbent, rooting at the lower nodes; first glume occasionally developed - ---- 15. P. NUTANS
gg. Culms erect; first glume always wanting - --- 13. P. PROPINQUUM
ff. Racemes terminal only on the main culm and branches.
g. Plants annual.
h. Spikelets with a broad firm notched margin --- 38. P. FIMBRIATUM
hh. Spikelets without a broad notched margin.
i. Fruit pale; spikelets not more than 1.5 mm. long.
j. Spikelets 0.8 mm. long, oblong-elliptic, glabrous, with raised margins; rachis zigzag --- 20. P. PARVIFLORUM
jj. Spikelets 1.1-1.6 mm. long, hemispherical or elliptic, sparsely to densely covered with globular or capitate hairs.
k. Blades 6-20 mm. wide; racemes 6-35, scattered on a long axis - -- -- 22. P. MICROSTACHYUM
kk. Blades not more than 2.5 mm. wide; racemes 1 or 2.
l. Spikelets subhemispheric, solitary, beaded with globular hairs, rarely glabrous - 18. P. MULTICAULE
ll. Spikelets elliptic or obovate, paired, pubes- cent with capitate hairs - - 19. P. CLAVULIFERUM
ii. Fruit dark brown, smooth and shining.
j. Spikelets suborbicular, or if obovate, 2.2-3 mm. long.
k. Culms slender, mostly 20-40 cm. high, decumbent-spreading; racemes 1-4, the rachis 1-2 mm. wide; sheaths and blades usually rather conspicuously papillose-pilose -34. P. CONVEXUM
kk. Culms mostly stout, commonly 40-60 cm. high; racemes commonly 4-11, the rachis 2- 2.5 mm. wide; sheaths and blades glabrous or nearly so _ - __ - _ 35. P. BOSCIANUM
jj. Spikelets obovate, 2 mm. long ------- 36. P. MELANOSPERMUM
gg. Plants perennial.
h. Culms creeping, rooting at the lower nodes. Spikelets solitary, not more than 1.8 mm. long.
i. Spikelets suborbicular.
j. Blades 1-6 cm. long; spikelets 1-1.2 mm. long. Plants stoloniferous- 23. P. ORBICULATUM
jj. Blades 5-13 cm. long; spikelets 1.7-1.8 mm. long. Subaquatic -25. P. HITCHCOCKII
ii. Spikelets ovate to more or less elliptic, acutish-- 24. P. JIMENEZII
hh. Culms not creeping, if rooting at the lower nodes the spikelets in pairs or more than 4 mm. long.
i. Plants stoloniferous, coarse, succulent; spikelets 4- 4.5 mm. long, solitary. Racemes usually numerous, arranged in a dense flabellate inflorescence - 27. P. FASCICULATUM
ii. Plants not stoloniferous, erect; spikelets not more than 3.9 mm. long, usually much less.
j. Fruit dark brown, smooth and shining.
k. Sterile lemma wrinkled just within the margins. 32. P. PLICATULUM
kk. Sterile lemma flat- 33. P. CENTRALE
ji. Fruit pale to stramineous, or if brown not shining, striate-roughened.
k. Spikelets 1.3-1.6 mm. long; culms usually slender.
l. Racemes 7-60, the lower ones 4-12 cm. long; culms 0.3-2 m. high; spikelets subhemispherical, 1.3-1.5 mm. long, pubescent -17. P. PANICULATUM
ll. Racemes 2-4, 2.2-4 cm. long; culms 20-27 cm. high; spikelets narrowly obovate or elliptic, 1.6 mm. long; glabrous - 21. P. STANDLEYI
kk. Spikelets 1.9 mm. long or more; culms coarse and robust, mostly 1-2 m. high.
1. Culms freely branching at maturity. Spike- lets elliptic, glandular-pubescent, 2-2.5 mm. long - -- 31. P. CORYPHAEUM
11. Culms simple or with a few simple branches.
m. Spikelets obovate or suborbicular, 1.9-3 mm. long.
n. Racemes 50-100, crowded; spikelets 1.9-2.2 mm. long, glabrous; fruit pale 30. P. DENSUM
nn. Racemes less than 30, commonly 10-16; spikelets 2.2-3 mm. long; fruit dark brown - -- 28. P. VIRGATUM
mm. Spikelets elliptic, acute, 3.5-3.9 mm. long. Second glume ciliate on the mar- gins toward the summit, otherwise glabrous..................29. P. ACUTUM