Plants annual; stoloniferous, mat-forming, without innovations,
without glands. Culms decumbent and rooting at the lower nodes, erect
portion (2)5-12(20) cm, often branched, glabrous or hairy on the lower internodes.
Sheaths pilose on the margins, collars, and at the apices, hairs 0.1-0.6
mm; ligules 0.3-0.6 mm; blades 0.5-2.5 cm long, 1-2 mm wide, flat
to involute, abaxial surfaces glabrous, adaxial surfaces appressed pubescent,
hairs about 0.2 mm. Panicles terminal and axillary, 1-3.5 cm long, 0.7-2.5
cm wide, ovate, open to somewhat congested; primary branches 0.1-0.5
cm, appressed to strongly divergent, glabrous; pulvini sparsely pilose
or glabrous; pedicels 0.2-1 mm, ciliate. Spikelets 4-13 mm long,
1-1.5 mm wide, linear-oblong, often arcuate, loosely imbricate, greenish-yellow
to purplish, with 12-35 florets; disarticulation acropetal, paleas persistent.
Glumes linear-lanceolate to lanceolate, hyaline; lower glumes
0.4-0.7 mm; upper glumes 0.8-1.2 mm; lemmas 1.4-2 mm, ovate, strongly
3-veined, veins greenish, apices acuminate; paleas 0.7-1.2 mm, hyaline,
keels scabridulous, apices acute to obtuse; anthers 2, 0.2-0.3 mm, brownish.
Caryopses 0.3-0.5 mm, ellipsoid, somewhat translucent, light brown. 2n
= 20.
Eragrostis hypnoides
grows along muddy or sandy shores of lakes and rivers
and in moist, disturbed sites, at 10-1600 m. It is native to the Americas, extending
from southern Canada to Argentina.
Annual mat-forming, runner-bearing herb without glands 2 - 24 cm tall Leaves: with open sheaths that have soft 0.1 - 0.6 mm long hairs on the margins and tip, and ligules that are 0.3 - 0.6 mm long. The blades are 0.5 - 2.5 cm long, 1 - 2 mm wide, flat or with margins rolling toward the upper surface of the midvein (involute), hairless beneath, appressed hairy (to 0.2 mm long) above. Inflorescence: terminal and axillary, branched (panicle), rising above upper leaves, 1 - 3.5 cm long, 0.7 - 2.5 cm wide, egg-shaped, open to somewhat crowded, with hairless primary branches 0.1 - 0.5 cm long. Fruit: a caryopsis, more or less transluscent light brown, 0.3 - 0.5 mm long, elliptic. Culm: 2 - 20 cm long, decumbent, rooting at lower nodes. The erect part is 2 - 20 cm tall, usually branched, and hairless or hairy along the lower internodes. Spikelets: loosely overlapping on a 0.2 - 1 mm long and hairy stalk, greenish yellow to purplish, 4 - 13 mm long, 1 - 1.5 mm wide, linear-oblong, usually arching, laterally compressed. Glumes: transparent, linear-lance-shaped to lance-shaped, single-veined, neither lobed nor awned, with a lower glume 0.4 - 0.7 mm long and an upper glume 0.8 - 1.2 mm long. Florets: twelve to 35 per spikelet, with two brownish anthers 0.2 - 0.3 mm long. Lemma: 1.4 - 2 mm long, egg-shaped with a pointed tip, usually hairless, with three strong greenish veins. Palea: transparent, 0.7 - 1.2 mm long, with a blunt to pointed tip and two minutely rough longitudinal ridges.
Similar species: Eragrostis hypnoides is easily distinguished from the other Eragrostis species in the Chicago Region, because it roots at the lower nodes and is mat-forming.
Flowering: mid August to late September
Habitat and ecology: Muddy, sandy or rocky areas along streams or around ponds that were flooded earlier in the season.
Occurence in the Chicago region: native
Etymology: Eragrostis is derived from the name of the Greek god of love, Eros, and agrostis, meaning grass. Hypnoides means "like the moss Hypnum."
Annual; stems creeping, rooting at the nodes, forming mats, sending up short culms 5-15 cm; lf-blades 1-4 cm נ1-3 mm; infl ovoid to subcylindric, 2-8 cm; peduncle glabrous; pedicels 1-3 mm; spikelets linear, 10-35-fld; fls perfect; lemmas 1.5-2 mm, glabrous, shining, almost hyaline, falling individually from the intact rachilla, on which the paleas persist; anthers 0.3 mm. Mud-flats and sandy shores; throughout most of the U.S. except the arid or mountainous regions, s. to Arg.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.