Erioneuron pilosum, the hairy woollygrass, hairy erioneuron or hairy tridens, is a short, perennial grass often occurring on overgrazed rangelands in the Americas. Within the familyPoaceae, it belongs to the subfamily Chloridoideae, which mainly occurs in arid tropical and subtropical grasslands.
Description Erioneuron pilosum is can be distinguished from most other grass species by this combination of features:
Normally it forms tufts up to tall, though usually it is shorter. Typically only one stem internode shows above the dense tuft of basal leaves. Sometimes it develops stolons. Leaves up to long usually are folded up their middles -- they are conduplicate -- and are much hardened, or "cartilaginous", along their margins. At blade bases there are tufts of hairs up to tall. Atop the leaf base wrapping around the stem, the sheath, there's a ligule composed of a tuft of hairs up to high). Spikelets up to long and containing up to 20 florets (usually about half that) are arranged in oval, compact panicles or racemes up to long. Florets, compressed from the sides, are purplish when immature but become pale possibly with a purplish tinge when mature. When they drop away, they disarticulate above the glumes. Glumes are about equal in size, up to long. A straight awn up to long occurs at the tips of lower lemmas; lemma veins are densely covered with long, soft hairs.
Distribution Erioneuron pilosum displays a conspicuously disjunct distribution. In North America it occurs in the United States' southwestern states from southern California to central Texas, and south to southern Mexico. In South America, it is found from Bolivia south into Argentina.
Habitat In the USA, Erioneuron pilosum lives on well-drained soils atop limestone, sand, caliche in open rangelands including overgrazed ones, in pastures, and where the soil generally is poor in nutrients. In California, it is described as inhabiting rocky slopes, ridges and pinyon-juniper woodlands at an elevation of . In Argentina it is found on rocky soils, in mountains, notably in Lihué Calel National Park, which is known for its tussock grasses. Also in Argentina, Erioneuron pilosum has been noted as an indicator species for calcareous soils.
Ecology Erioneuron pilosum is a host for caterpillars of the Uncas skipper, Hesperia uncas.
Seed-eating birds feed on the species' grains, and small mammals use it for nesting material. Deer avoid it as a food.
Human interactions
In gardens Erioneuron pilosum is described as a tufted perennial with a "lovely fluffy inflorescence" that looks good in short grass prairie gardens, where it grows to about 30 cm tall (1 foot). A nursery selling the species further states that it can provide a good matrix in which to establish wildflowers, for example combining it with the wildflowers Winecup, Prairie Verbena, Four-nerve Daisy, Blanketflower and Missouri Primrose. Among these wildflowers it contributes an interesting contrast with its texture.
On rangelands Erioneuron pilosum is one of the shortest and least productive grasses in terms of providing forage for livestock, though sheep and goats with their small mouths feed on it to a limited extent. It provides minimal protection to soil from erosion.
Taxonomy In 1862, Erioneuron pilosum, under the basionym Uralepis pilosa, was first described by Samuel Botsford Buckley.
Older literature sometimes mention varieties of Erioneuron pilosum, but currently the three varieties listed in the 1997 revision of the genus are listed among the taxon's 30 synonyms.
The formal description of the genus Erioneuron by Nash in 1903 was based on Erioneuron pilosum.
Etymology The genus name Erioneuron derives from the Greek erion, meaning "wool", and neuron, meaning "nerve". Thus "hairy-nerved", describing well the long-haired florets of the genus's species.
The species name pilosum derives from the Latin pilus, meaning "hair". The -um is added to decline the word's adjective neuter form, resulting in the meaning "hairy". This undoubtedly refers to the species' hairy lemmas and other parts.
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