|Mary E. Barkworth|
Plants perennial or annual; tufted
or cespitose, sometimes stoloniferous, perennial species sometimes rhizomatous.
Culms 5-250 cm, erect or decumbent; nodes usually villous or pilose,
particularly the upper nodes. Sheaths open, glabrous or pilose, lower
sheaths often glabrous basally and pilose distally, margins sometimes villous
or pilose, upper sheaths often glabrous even if the lower sheaths are pilose;
ligules 0.5-5 mm, membranous, lacerate or ciliate. Inflorescences
terminal, spikelike panicles of reduced, disarticulating branches, exceeding
the upper leaves; branches with 3 spikelets, appressed to the rachises,
bases straight, seated in a ciliate, cuplike structure, sometimes with a 0.5-2
mm callus, calluses pilose, axes not extending past the distal florets; disarticulation
at the base of the branches, leaving the zig-zag rachises. Lateral spikelets
of each branch shortly pedicellate, with 1-4(5) sterile or staminate florets;
glumes almost as long as the florets, deeply cleft into 2 or more lobes,
with 1 or more dorsal awns; lemmas membranous, hyaline. Central spikelets
sessile, with 1 pistillate or bisexual floret; glumes shorter than the
florets, rigid, indurate and fused basally, apices with 2 or more lobes; lemmas
membranous, awned or unawned. x = 9. Named for Auguste François
César Prouvençal de St.-Hilaire (1779-1853), a French explorer,
botanist, and entomologist.
Hilaria is a genus of 10 species that ranges from the southwestern United States to northern Guatemala, growing primarily in dry grasslands and desert areas. Most of the species are important forage species. The stoloniferous species are important soil binders.
Hilaria is interpreted here as having two groups, the Hilaria group and the Pleuraphis group [= Pleuraphis Torr.]. These are sometimes treated as separate genera but, although they differ consistently in some morphological characters, their overall similarity is striking. One molecular study (Columbus et al. 1998, 2000) has included representatives of both groups. It showed them to be sister taxa; there seems little value in promoting each to generic rank.
In the key and descriptions below, the term fascicle refers to a branch and its spikelets. Actual branch lengths are much shorter and harder to measure.
Glumes thickened, indurate, and conspicuously fused at the base; central spikelets with 1 pistillate floret (Hilaria group) (2)
Glumes papery or membranous throughout, not conspicuously fused at the base; central spikelets with 1 bisexual floret (Pleuraphis group) (3)
Glumes pale to purplish, those of the lateral spikelets with dark glands confined to the base or lacking, awned from below midlength ..... 4. H. belangeri
Glumes gray to dark brown, those of the lateral spikelets evenly covered with dark glands, awned from above midlength ..... 5. H. swallenii
Glumes of the lateral spikelets flabellate, the awns not exceeding the apical lobes; cauline nodes usually only shortly pubescent, sometimes glabrous ..... 1. H. mutica
Glumes of the lateral spikelets lanceolate or parallel-sided, the awns exceeding the apical lobes; cauline nodes pilose, villous, or glabrous (4)
Lower cauline internodes tomentose ..... 2. H. rigida
Lower cauline internodes glabrous ..... 3. H. jamesii
1. Hilaria mutica (Buckley) Benth.
Plants perennial; cespitose, rhizomatous. Culms 30-60 cm, erect, geniculate at the middle nodes; nodes glabrous or pubescent, hairs to 0.3 mm. Sheaths glabrous or sparsely pilose on the margins; ligules 0.5-2 mm, lacerate; blades 2-15 cm long, 2-4 mm wide, mostly scabrous on both surfaces, with papillose-based hairs behind the ligules. Panicles 4-8 cm; fascicles 5-8 mm. Lateral spikelets with 1 or 2(4) staminate florets; glumes not conspicuously fused basally, thin, papery, flabellate, dorsally awned, awns not exceeding the apices, apical lobes rounded, ciliate to finely laciniate, veins not or scarcely excurrent; anthers 3, 2.5-3.5 mm. Central spikelets with 1 bisexual floret; glumes with 1 or more divergent, dorsal awns, apical lobes, ciliate to finely laciniate, veins excurrent; lemmas exceeding the glumes, bilobed, mucronate. 2n = 36, 54.
Hilaria mutica grows in level upland areas and desert valleys subject to occasional flooding but lacking permanent streams. Its range extends into northern Mexico. Although H. mutica has moderate forage value, its palatability is low and it is frequently infected with ergot.
2. Hilaria rigida (Thurb.) Benth.
Plants perennial; cespitose, sometimes rhizomatous. Culms 35-250 cm, decumbent, much branched above the base, becoming almost woody; upper nodes glabrous or villous, hairs to 1.5 mm; lower internodes tomentose. Ligules 1-2 mm, densely ciliate; blades 2-10(16) cm long, 2-5 mm wide, flat basally, involute distally. Panicles 4-12 cm; fascicles 6-12 mm. Lateral spikelets with 2-4 florets, lower 2 florets staminate, other florets (if present) usually sterile; glumes thin, membranous, not fused at the base, lanceolate or parallel-sided, 7-veined, awned, awns exceeding the glume apices, apices 2-4-lobed, lobes acute to rounded, long-ciliate, sometimes with 1-3 excurrent veins that form additional slender awns to 1.8 mm; lower glumes with dorsal, divergent awns; upper glumes with subapical awns; anthers 3, 4-4.5 mm. Central spikelets equaling or exceeding the lateral spikelets, with 1 stipitate, bisexual floret; glumes thin, membranous, narrow, deeply cleft into few-several acuminate, ciliate lobes and slender awns; lemmas often exceeding the glumes, thin, ciliate, 2-lobed, midveins excurrent. 2n = 18, 36, 54.
Hilaria rigida grows in deserts and open juniper stands, at low elevations, from the southwestern United States to central Mexico. Although almost shrubby, it is very popular with pack horses.
3. Hilaria jamesii (Torr.) Benth.
Plants perennial; strongly rhizomatous or stoloniferous. Culms 20-65 cm, erect, bases much branched; nodes usually pilose or villous, sometimes glabrous; lower internodes glabrous. Sheaths glabrous, sometimes slightly scabrous; collars pilose at the edges; ligules 1.5-5 mm, often laciniate; blades 2-20 cm long, 2-4 mm wide, involute and curled when dry, sparsely villous behind the ligules, abaxial surfaces scabridulous, adaxial surfaces scabrous. Panicles 2-6 cm; fascicles 6-8 mm. Lateral spikelets with 3 staminate florets; glumes thin, membranous, lanceolate or parallel-sided, not conspicuously fused at the base, apices acute to rounded, often ciliate, veins rarely excurrent; lower glumes dorsally awned, awns exceeding the apices; anthers 3, about 5 mm. Central spikelets with 1 bisexual floret; glumes with excurrent veins forming distinct awns; lemmas exceeding the glumes, ciliate, the midveins sometimes excurrent. 2n = 18, 36.
Hilaria jamesii is endemic to the southwestern United States, and grows in deserts, canyons, and dry plains. It has medium grazing value but low palatability. It is usually less pubescent than H. rigida, the difference being most marked on the lower cauline nodes.
4. Hilaria belangeri (Steud.) Nash
Plants perennial; cespitose, usually stoloniferous. Culms 5-35 cm, erect; nodes villous. Sheaths striate, glabrous; ligules 1-3 mm, often lacerate; blades 3-15 cm long, 1-3.5 mm wide, adaxial surfaces sparsely pilose, hairs papillose-based, margins sparsely pilose basally, with similar hairs. Panicles 2-4 cm; fascicles 5-8 mm. Lateral spikelets with 2(3) staminate florets, or 1 sterile floret; glumes unequal, thick,indurate, and conspicuously fused basally, thinner distally, asymmetrically lobed, scabrous, pale to purplish, bases sometimes spotted with a few dark glands, margins wide, hyaline, awns 1 or more, attached below midlength, equaling or exceeding the central spikelets, antrorsely scabrous; lower glumes wider, more deeply lobed, with longer awn(s) than the upper glumes; anthers 3, 3-3.7 mm. Central spikelets as long as or longer than the lateral spikelets, with 1 pistillate floret; glumes terminating in 1 or more antrorsely scabrous awns. 2n = 36, 72, 74.
Both varieties of Hilaria belangeri are found on mesas and plains within the regions indicated.
Plants stoloniferous; blades 3-10 cm long, 1-2 mm wide; ligules about 1-1.5 mm long ..... var. belangeri
Plants not stoloniferous; blades 3-15 cm long, to 3.5 mm wide; ligules 2.5-3 mm long ..... var. longifolia
Hilaria belangeri (Steud.) Nash var. belangeri
Plants stoloniferous. Ligules 1-1.5 mm; blades 3-10 cm long, 1-2 mm wide.
Hilaria belangeri var. belangeri grows from Arizona to Texas, and south through Mexico. It was the dominant grass on Texas shortgrass prairies.
Hilaria belangeri var. longifolia (Vasey) Hitchc.
Plants not stoloniferous. Ligules 2.5-3 mm; blades 3-15 cm long, to 3.5 mm wide.
Hilaria belangeri var. longifolia is more restricted than var. belangeriin its distribution, growing from Arizona to Texas, and south to northwestern Mexico.
5. Hilaria swallenii Cory
Swallen's Curly Mesquite
Plants perennial; stoloniferous. Culms 10-35 cm, erect; nodes villous. Sheaths slightly scabrous; ligules 2-2.2 mm; blades to 8 cm long, 1-2 mm wide, mostly basal, both surfaces scabrous, sometimes also sparsely pilose. Panicles 1-4 cm, with 2-8 fascicles; fascicles 6.5-8 mm. Lateral spikelets with 2 florets, lowest florets usually sterile, distal florets staminate; glumes unequal, thick, indurate, and conspicuously fused basally, mostly gray to dark brown, evenly and sparsely to densely spotted with dark glands, awned from above midlength, margins hyaline; anthers 3, 3-3.5 mm. Central spikelets with 1 pistillate floret; lemmaselliptic basally, narrower and parallel-sided distally. 2n = 54, 72.
Hilaria swallenii grows on dry plains and rocky mesas in New Mexico, Texas, and northern Mexico. It is considered better forage than H. belangeri, but it is less important because it is less common.