About 500 species, in temperate and tropical regions. The old English name, Panic or Panic-grass, is often applied to any of the species. Type species: Panicum miliaccum L.

Spikelets on one side of the rachis on short pedicels forming 1-sided racemes.

I.

Paspaloidea.

Spikelets arranged in panicles, the divisions sometimes strict and narrow but not 1-sided.

' Basal leaf-blades long and narrow, similar to those of the stem; no rosulate tufts of leaves in the fall; spikelets lanceolate to ovate, acute to acuminate, rarely obtuse.

Spikelets manifestly tuberculate.

II.

Verrucosa.

Spikelets not tuberculate.

Basal leaf-sheaths round or but little flattened, not keeled.

Annuals.

III.

Capillaria.

Perennial by long rootstocks or stolons.

Rootstocks and stolons naked or with a few large scales.

IV.

Halophila.

Rootstocks and stolons with numerous small broad scales.

V.

Virgata.

Basal leaf-sheaths much compressed, broad, keeled, often equitant.

VI.

Agrostoidea.

Basal leaf-blades unlike those of the culm, ovate to ovate-lanceolate; perennial by rosulate tufts which form in the fall at the base of the culms; spikelets elliptic to spheric, usually

obtuse, rarely acute, never acuminate.

VII.

DlCHOTOMA.

I. Paspaloidea.

Spikelets ovate, acute, about 1 1/4" long; an aquatic grass.

1.

P. hemitomon.

Spikelets oval or obovate, obtuse, about 1 1/2" long.

2.

P. obtusum.

II. Verrucosa.

A single species in our range; spikelets tuberculate.

3.

P.

verrucosum.

III. Capillaria.

Spikelets lanceolate or elliptic, 1 3/4" long or less.

Leaves glabrous.

4.

P.

dichotomiflorum.

Leaves pubescent.

Spikelets 1 1/4" long or less, panicles broad.

Panicle large and diffuse, occupying more than one half of the plant.

5.

P.

capillare.

Panicle not occupying over one third of the plant, usually exserted from the sheath.

Spikelets 1" long or more; culms stout; blades 4"-5" wide

7.

P.

Gattingeri.

Spikelets less than 1" long; blades 1"-3" wide.

8. P.

philadelphicum.

Spikelets 1 1/2"-1 3/4" long.

Panicle narrow, its branches ascending or nearly erect.

9.

P.

flexile.

Panicle open, diffuse, broader than long, its branches spreading or the lower ones

reflexed.

6.

P.

barbipulvinatum.

Spikelets ovate, 2"-2 1/2" long.

10.

P.

miliaceum.

IV. Halophila.

Culms densely tufted; spikelets about 2 1/4" long.

11.

P.

amarulum.

Culms scattered, from stout branching rootstocks; spikelets 2 1/2"-3" long.

12.

P.

amarum.

V. VlRGATA.

Stems tall, simple; panicle usually ample.

13.

P.

virgatum.

VI. Agrostoidea.

Rootstocks present.

14.

P.

anceps.

Rootstocks wanting.

Fruiting scale sessile.

Panicle broad, open, its branches spreading.

Ligule naked; culms finally much-branched; spikelets numerous.

I5.

P.

agrostoides.

Ligule ciliate; culms simple or sparingly branched; spikelets few.

17.

P.

longifolium.

Panicle oblong, narrow, dense, its branches erect.

16.

P.

condensum.

Fruiting scale distinctly stalked.

18.

P.

stipitatum.

VII. DlCHOTOMA.

Culms simple, or with basal branches and panicles only; not fasciculately branched later.

Spikelets acute, usually over 1 1/2" long, the second and third scales extending beyond the

fruiting scale.

19.

P.

depanperatum.

Spikelets obtuse, rarely acutish, 1 1/2" long or less; outer scales not exceeding fruiting scale.

Secondary panicles present. ,

Panicle-branches erect; spikelets obtuse, about 1 1/2" long.

20.

P.

perlongum.

Panicle branches spreading; spikelets acutish, i"-i 1/4" long.

21.

P.

linearifoliutn.

Secondary panicles wanting.

Leaf-sheaths glabrous or merely ciliate on the margins.

Blades ciliate their entire length; plants yellowish green.

24.

P.

ciliatum.

Blades not ciliate or sparingly so at the very base; plants green or grayish green.

Spikelets less than 1" long.

Panicle much longer than broad; upper blades not smaller than the lower ones.

32.

P.

polyanthes.

Panicle nearly as long as broad, upper blades smaller than the lower ones.

31.

P.

sphaerocarpon.

Spikelets 1" long or more.

Blades linear, less than 2 1/2" wide.

22.

P.

Wetneri.

Blades linear-lanceolate, 3"-10" wide.

Panicle narrow, its branches appressed.

64.

P.

xanthophysum.

Panicle broad, open, its branches spreading.

23.

P.

Bicknellii.

Leaf-sheaths spreading-hirsute.

Spikelets glabrous, 3/4" long; culms hirsute.

25.

P.

strigosum.

Spikelets pubescent, about 1" long; culms glabrous.

26.

P.

laxiflorum.

Culms simple only at first; later with fasciculate branches at the upper nodes.

Middle blades of main culm less than 8" wide, the base rounded to subcordate.

Blades of the main culm usually elongated and narrowed at both ends.

Plants large; culms over 3° long; leaf-blades up to 8' long.

Spikelets 1 1/4" long, very acute, strongly nerved.

69.

P.

scabriusculum.

Spikelets 1 1/2" long, barely acute, less strongly nerved.

70.

P.

aculeatum.

Plants small; culms under 3° long; leaf-blades rarely exceeding 4' long.

Spikelets pubescent, narrowed at the base.

Spikelets 1" long; mature state of the blades involute.

28

. P.

aciculare.

Spikelets 1 1/4" long; mature blades flat, or involute only on the margins.

Nodes not barbed; branches of the panicle spreading.

27.

P.

angustifolium.

Nodes barbed; branches of the panicle ascending.

29.

P.

consanguineum.

Spikelets glabrous, not narrow at the base.

30.

P.

Bushii.

Blades of the culm not elongated nor conspicuously narrowed at the base.

Spikelets less than 1 1/2" long.

Spikelets glabrous.

Spikelets strongly nerved, acute; blades up to 8' long.

69.

P.

scabriusculum.

Spikelets relatively obscurely nerved, obtuse; blades rarely exceeding 4' long.

Nodes densely barbed; spikelets about 3/4" long.

38.

P.

microcarpon.

Nodes naked, or rarely the lowermost ones sparingly barbed.

Spikelets usually less than 3/4" long.

42.

P.

octonodum.

Spikelets 1" long:

Obovoid; culms puberulent.

60.

P.

Nashianum.

Elliptic; culms glabrous.

Culms erect, the branches fasciculate near the middle.

35.

P. dichotomum.

Culms at length long and trailing, branches fasciculate at all the nodes.

36.

P. lucidum.

Spikelets 1 1/4" long.

37.

P. yadkinense.

Spikelets pubescent.

Sheaths glabrous, the margins ciliate, or the basal ones sometimes pubescent.

Blades velvety.

39.

P. annulum.

Blades not velvety.

Ligule 1/2" long or less.

Spikelets less than 1" long.

Culms slender, the leaf-blades 1' long or less; spikelets elliptic.

33.

P. ensifoliiuii.

Culms stouter, the leaf-blades larger; spikelets nearly globose.

Panicle longer than broad; upper leaf-blades not smaller than

the lower.

32.

P. polyanthes.

Panicle nearly as long as broad; upper blades smaller than the lower ones..

Blades less than 4" wide, glabrous.

34.

P. tenue.

Blades exceeding 4" wide, ciliate on the margins toward

the base.

31.

P. sphaerocarpon.

Spikelets over 1" long.

Culms puberulent.

71.

P. Ashei.

Culms glabrous.

Leaf-blades cordate, usually over 5" wide

72.

P. commiitatum.

Leaf-blades not cordate at the base, usually less than 5" wide.

Blades erect, ciliate toward the base; fruiting scale not exceed-

ing the others.

40.

P. boreale.

Blades spreading, glabrous; fruiting scale exceeding the other

scales.

41.

P. mattamuskeetense.

Ligule 1"-2 1/2" long.

Spikelets over 1" long.

48.

P. scoparioides.

Spikelets less than 1" long.

Panicle much longer than broad.

Spikelets less than 3/4" long, almost globose when mature,

sparsely pubescent with short hairs.

43.

P. paucipilum.

Spikelets over 3/4" long, elliptic, densely pubescent with long hairs.

44.

P. spretum.

Panicle as long as broad.

45.

P. Lindheimeri.

Sheaths pubescent.

Sheaths merely puberulent.

Spikelets elliptic, over 1" long.

71.

P. Ashei.

Spikelets obovoid, 1" long.

60.

P. Nashianum.

Sheaths pubescent with longer hairs.

Plants velvety.

Spikelets over 1" long.

Culms stout, a broad bare ring below each node; spikelets i"-1 1/4"

long; primary panicles exceeding 3' long.

67. P. scoparium.

Culms slender; no conspicuous bare ring; spikelets 1 1/4 - 1 1/2" long;

panicle less than 3' long.

68.

P. malacophyllnm.

Spikelets less than 1" long.

Hairs on the sheaths long and shaggy; ligule over 1" long.

55.

P. lanuginosum.

Hairs on the sheaths short and inconspicuous; ligule less than ;

long.

39.

P. annulum.

Plants not velvety.

Spikelets ovate, pointed; blades and panicles usually 5' long or more.

69.

P. scabriusculum.

Spikelets not as above; blades and panicles shorter.

Spikelets less than 1" long.

Pubescence spreading.

Blades glabrous above or nearly so.

54.

P. tennesseense.

Blades pubescent on the upper surface.

Upper surface of blades with short appressed hairs.

47.

P. huachucae.

Upper surface with long erect hairs 1 1/2" long or more.

Culms forming branches when primary panicles are mature; spikelets 3/4" long.

Panicle 1'-1 1/2' long, its axis minutely pubescent.

52.

P. meridionale.

Panicle 2'-3' long; axis hirsute. 51. P. implicatum.

Culms forming branches before maturity of primary

panicles; spikelets 1" long.

50.

P. praecocius.

Pubescence not spreading.

Ligule obsolete; culms villous-puberulent, at least below.

Culms with 2 or 3 primary leaves, the blades 1 1/2" wide or less, up to 3'-4' long, branches crowded at the base.

53.

P. Owenae.

Culms with 4-6 primary leaves, the blades 2"-4" wide, usually less than 3' long, branches at all the nodes.

Culms erect, rigid; plants grey green.

58.

P. columbianum.

Culms weak, fasciculately decumbent and forming

mats; plant blue-green.

59.

P. tsugetorum.

Ligule 1/2" long or more; culms, at least at the base, pubescent with long stiff appressed hairs.

Blades glabrous on the upper surface; spikelets about

V2" long.

46.

P.

leucothrix.

Blades pubescent on the upper surface with long hairs;

spikelets exceeding l/2" long.

52.

P.

meridionale.

Spikelets 1" long or more.

Pubescence spreading.

Autumnal state erect; pubescence papillose-hispid; upper sur-

face of blades glabrous or nearly so.

48.

P.

scoparioides.

Autumnal state prostrate; pubescence hirsute; upper surface of

blades long-hairy. 49.

P.

villosissimum.

Pubescence not spreading.

Panicle 11/2'-2' long, oblong, dense; spikelets 1" long.

56.

P.

Addisoni.

Panicle 2l/2'-3l/2 long, broadly ovoid, open; spikelets 1 1/4"

long.

57.

P.

Commonsianum.

Spikelets 1 l/2" long or more.

Spikelets hirsute with long hairs, the first scale usually over 1/2 as long as the

spikelet, often narrow and attenuate.

61.

P.

Liebergii.

Spikelets glabrous, or if pubescent the hairs short.

Leaf-blades glabrous, at least on one surafce.

Panicle narrow, its branches usually appressed.

64.

P.

xanthophysum.

Panicle broad, nearly as wide as long.

Spikelets 1 1/2" long; blades commonly much elongated.

Blades rough, usually erect, not ciliate.

70.

P.

aculeatum.

Blades smooth, spreading, ciliate.

73.

P.

niutabile.

Spikelets over 1 1/2" long; blades not elongated.

Blades softly and densely pubescent beneath with short hairs.

Culms papillose-hispid with appressed or ascending hairs; blades

usually 6" wide or more.

66.

P.

Ravenelii.

Culms villous; blades 5" wide or less.

63.

P.

oligosanthes.

Blades glabrous, or rarely puberulent beneath.

62.

P.

Scribnerianum.

Leaf-blades pubescent on both surfaces.

Blades erect, less than 3" wide; pubescence hispid.

65.

P.

Wilcoxianum.

Blades spreading, exceeding 3" wide; pubescence soft.

68.

P.

malacophyllum.

Middle blades of the main culm more than 8" wide, usually cordate and clasping at the base.

Spikelets less than 1l/2" long.

Blades glabrous on both surfaces.

Spikelets less than 1" long; culms simple.

32.

P.

polyanthes.

Spikelets more than 1" long; panicle nearly as broad as long; culms branched.

Sheaths papillose-hispid, especially the terminal ones.

76.

P.

clandestinum.

Sheaths glabrous.

72.

P.

commutation.

Blades densely villous on both surfaces.

67.

P.

scoparium.

Spikelets 1 l/2" long or more.

Panicle narrow, its branches appressed, rarely a little spreading.

64.

P. xanthophysum.

Panicle open, its branches spreading.

Blades lanceolate, thick, glabrous above, densely pubescent on the lower surface with

short spreading hairs.

66.

P.

Ravenelii.

Blades thin, ovate-lanceolate, glabrous, or sometimes sparsely pubescent.

Nodes barbed.

75.

P.

Boscii.

Nodes naked.

Spikelets 1 1/2" long; blades rarely exceeding 8" wide.;

73.

P.

mutabile.

Spikelets nearly 2" long; blades exceeding 10" wide.

74.

P.

latifolium.