Eustachys

Plants perennial; cespitose, shortly rhizomatous and often stoloniferous. Culms 20-150 cm, erect or decumbent, flattened, glabrous; internodes hollow. Leaves basal and cauline; sheaths open, keeled, strongly compressed, distinctly distichous, equitant; ligules to 0.5 mm, scarious, densely short ciliate; blades flat or folded, erect to spreading, both surfaces usually glabrous, sometimes scabrous or scabridulous. Inflorescences terminal, exceeding the upper leaves, panicles of 1-36 non-disarticulating spikelike branches; branches digitately arranged, axes triquetrous, with spikelets in 2 rows on the abaxial sides of the branches. Spikelets solitary, diverging strongly from the branch axes, laterally compressed, sessile or subsessile, with 2-3 florets; lowest florets bisexual; second florets usually reduced to a stipitate empty lemma, occasionally with a palea, staminate if a third floret is present; third florets, if present, sterile and usually rudimentary, stipitate; disarticulation above the glumes. Glumes unequal, 1-veined; lower glumes somewhat smaller than the upper glumes, narrow, acuminate; upper glumes almost as long as the spikelets, flattened, scarious, glabrous, green, pale, or purplish, veins antrorsely scabrous, apices truncate, bilobed, or bifid, often mucronate; lowest lemmas cartilaginous, light to dark brown, scabridulous distally, 3-veined, unawned, mucronate, or with a single awn, awns to 1.2 mm; paleas equaling or slightly shorter than the lemmas, glabrous, 2-veined, veins keeled, shortly ciliate or scabridulous; anthers 3, deep purple to purple-red. Caryopses 1-1.7 mm, trigonous-ellipsoid, glabrous, translucent when fresh, pale to slightly reddish-purple-tinged, x = 10.

Distribution

Pa., Miss., Tex., La., Calif., Puerto Rico, Virgin Islands, Ala., N.C., S.C., Pacific Islands (Hawaii), Ga., N.J., N.Y., Fla.

Discussion

Eustachys, as treated here, is a genus of approximately 12 species, most of which are native to the Western Hemisphere; four are native to the Flora region and three have been introduced. It is, in many ways, morphologically similar to Chloris, with the placement of a few species being problematic. Molecular data (Alice et al. 2000) support its recognition as a distinct genus, but the relationships between it, Chloris sensu stricto, and Cynodon are not clear.

Selected References

Alice, L.A., G.G. Borneo, and K.W. Hilu. 2000. Systematics of Chloris (Chloridoideae; Poaceae) and related genera: Evidence from nuclear ITS and chloroplast matK sequences. Amer. J. Bot. 87, Suppl.: 108-109

Anderson, D.E. 1974. Taxonomy of the genus Chloris (Gramineae). Brigham Young Univ. Sci. Bull., Biol. Ser. 19:1-133.

Lower Taxa

Eustachys caribaea, Eustachys distichophylla, Eustachys floridana, Eustachys glauca, Eustachys neglecta, Eustachys petraea, Eustachys retusa

Key

1	Lateral veins of the lowest lemma in each spikelet usually glabrous, occasionally with a few short, stiff hairs	Eustachys glauca
1	Lateral veins of the lowest lemma in each spikelet pubescent.	> 2
2	Keels of the lowest lemma in each spikelet glabrous.	> 3
3	Spikelets 1.5-2.1 mm long; panicles with 6-15 branches; branches 4-10 cm long, straight, somewhat stiff; leaf blades 5-10 mm wide	Eustachys retusa
3	Spikelets 2.4-3 mm long; panicles with 10-36 branches; branches 6-15 cm long, flexible; leaf blades 10-15 mm wide	Eustachys distichophylla
2	Keels of the lowest lemma in each spikelet pubescent.	> 4
4	Spikelets 1.5-2.5 mm long; lowest lemma in each spikelet mucronate.	> 5
5	Lowest lemma in each spikelet dark brown, the lateral veins with appressed hairs shorter than 0.5 mm	Eustachys petraea
5	Lowest lemma in each spikelet tawny to reddish-brown, the lateral veins with spreading hairs longer than 0.5 mm	Eustachys caribaea
4	Spikelets 2.6-3.7 mm long; lowest lemma in each spikelet awned, awns 0.4-1.2 mm.	> 6
6	Panicle branches 1-3; awns of lowest lemma in each spikelet 0.4-0.6 mm long; spikelets 3-3.7 mm long	Eustachys floridana
6	Panicle branches (3)4-9; awns of lowest lemma in each spikelet 0.7-1.2 mm long; spikelets 2.6-3 mm long	Eustachys neglecta