22. Milium. Awn none. Flower small, ovoid, without callus.

[+][+] Fruiting glume thin and membranous; outer glume smaller or minute.

23. Muhlenbergia. Flower mostly hairy at base, the glume mucronate or awned.

24. Brachyelytrum. Rhachis produced into a bristle above. Outer glumes very small, the flowering one long-awned. Stamens 2.

[*][*] Flowering glume awnless or short-awned, loosely embracing the grain, thin, the lower glumes complicate carinate; spikelets in dense spike-like panicles, the rhachis not produced.--PHLEOIDEae.

25. Heleochloa. Awns none. Spikes short and scarcely exserted.

26. Phleum. Glumes somewhat truncate, mucronate or short awned. Spike cylindric.

27. Alopecurus. Lower glumes united at base, the flowering awned on the back. Palet none. Spike cylindric.

[*][*][*] Glumes membranous, the lower rarely strongly complicate, the flowering with a dorsal awn or awnless; spikelets variously panicled.--AGROSTEae.

[+] Flowering glume 1- (rarely 3-) nerved, awnless; grain loosely enclosed or naked.

28. Sporobolus. Culms wiry or rigid. Leaves involute.

[+][+] Flowering glume 3--5 nerved, mostly awned; grain enclosed.

[++] Rhachis not reduced above the single flower.

29. Agrostis. Spikelets in an open panicle.

30. Polypogon. Empty glumes long-awned. Panicle spike-like.

31. Cinna. Spikelets flattened, in a loose panicle. Palet 1-nerved.

Stamen 1

[++][++] Rhachis bearing a rudimentary second flower or short bristle (except in species of n. 33).

32. Apera. Flowering glume bifid, awned. Panicle very loose and delicate.

33. Calamagrostis. Flowers hairy-tufted at base. Glumes membranaceous.

Palet thin.

34. Ammophila. Spikelets large. Flowers hairy tufted at base. Glumes and palet chartaceous.

Tribe VII. AVENEae. Spikelets 2--several-flowered, panicled, the rhachis or base of the flowers often bearded; upper flower imperfect or rudimentary (except in n. 37). Flowering glume bearing a twisted, bent or straight awn on its back or below the apex.

[*] One of the flowers staminate only.

35. Arrhenatherum. Lower flower staminate, long awned; middle flower perfect, nearly awnless; the upper rudimentary.

36. Holcus. Flowers 2, the lower perfect, awnless, the upper staminate, awned.

[*][*] Flowers all perfect or the uppermost usually rudimentary.

37. Aira. Spikelets very small, in a diffuse panicle. Flowers 2, perfect, awned toward the base.

38. Deschampsia. Spikelets 2-flowered, with a hairy rudiment. Glumes thin-scarious, the flowering one erose-truncate awned near the middle.

39. Trisetum. Spikelets 2--several-flowered. Flowering glume thin, compressed, carinate, 2-toothed, awned above by the excurrent mid nerve.

40. Avena. Spikelets 2--several-flowered. Flowering glume hard and firm, rounded on the back, 5--9 nerved, the mid-nerve long-excurrent at or below the 2-toothed apex.

41. Danthonia. As Avena, but the 3 middle nerves of the flowering glume running into a flattish twisted awn from between the teeth.

Tribe VIII. CHLORIDEae. Spikelets 2--several-flowered with one or more of the upper flowers imperfect (flower 1 and perfect in n. 45) arranged in 2 rows upon the rhachis of a 1-sided spike.

[*] Spikelets with one perfect flower.

42. Cynodon. Spikes 3--5, slender, digitate. Flower and the rudiment awnless.

43. Ctenium. Spike solitary, terminal. Flowers 4--6, the middle one perfect.

44. Gymnopogon. Spikes filiform, racemose. Spikelets remote, of a perfect flower and an awned rudiment.

45. Schedonnardus. Spikes 3--9, slender, scattered, distant. Spikelets small, 1-flowered awnless.

46. Bouteloua. Spikes scattered (rarely 1 and terminal), dense. Glume of perfect flower 3-toothed. Rudimentary flowers 1--3 awned.

[*][*] Spikelets with two or more perfect flowers; awns none.

47. Eleusine. Spikes digitate, dense.

48. Leptochloa. Spikes racemose, slender. Spikelets small, alternate.

[*][*][*] Spikelets dicious; spikes small, very dissimilar.

49. Buchloe. Pistillate spikes capitate, sessile, the spikelets 1-flowered; staminate spikes (2 or 3) on a peduncle, the spikelets 2--3-flowered.

Tribe IX. FESTUCEae. Spikelets few--many-flowered, panicled, the uppermost flowers often imperfect or abortive. Glumes pointless or the flowering ones tipped with a straight awn or bristle.

[*] Flowering glume 1--3 nerved, 2--3-toothed. Rhachis short-bearded or glabrous.

50. Triodia. Rhachis of the spikelet bearded. Nerves of the flowering glume 3, villous, at least the middle one more or less excurrent.

51. Diplachne. Rhachis glabrous. Glume 1--3-nerved, with 2 small teeth, and a short awn in the cleft.

[*][*] Glume 3-nerved, entire or 2-toothed and mucronate between the teeth. Rhachis and flowers long-villous. Tall reeds with ample panicles.

52. Phragmites. Spikelets 3--7-flowered, lowest flower naked, staminate or neutral. Glume entire.

53. Arundo. As n. 52, but flowers all perfect. Glume bifid.