Arizona Signalgrass

Panicum arizonicum Scribn. & Merr. ; Merrill, Circ. U. S. Dep
Agr. Agrost. 32: 2. 1901.
Panicum dissitiflorum Vasey, in S. Wats. Proc. Am. Acad. 24: 80, hyponym. . 1889.
Panicum f us cum majus Vasey, Bull. U. S. Dep. Agr. Bot. 8: 26. 1889.
Panicum fas ciculatum dissitiflorum Vasey; Merrill, Circ. U. S. Dep. Agr. Agrost. 32: 2, as synonym.
1901. Panicum arizonicum tenue Scribn. & Merr.; Merrill, Circ. U. S. Dep. Agr. Agrost. 32: 3. 1901. Panicum arizonicum laeviglume Scribn. & Merr.; Merrill, Circ. U. S. Dep. Agr. Agrost, 32: 3. 1901. Panicum arizonicum majus Scribn. & Merr.; Merrill, Circ. U. S. Dep. Agr. Agrost. 32: 3. 1901.
Plants erect or ascending, sometimes decumbent at base and rooting at the lower nodes, branching at the base arid lower nodes; culms 20-60 cm. high, glabrous except below the panicle, the nodes sometimes slightly pubescent; leaf-sheaths shorter than the internodes or the upper often overlapping, rather loose, glabrous to strongly papillose-hispid; Hgule a ring of hairs about 1 mm. long; blades rather thin, ascending or spreading, 5-15 cm. long, 6-12 mm. wide, rounded at base, glabrous on both surfaces, or scabrous to papillose-hispid beneath, the scabrous, thin, cartilaginous margin usually papillose-ciliate at base; panicles usually long-exserted, 7-20 cm. long, the solitary', ascending, slender branches loosely flowered, the spikelets borne on very short appressed branchlets, the pedicels and axes of branchlets, branches, and the entire panicle finely pubescent and also copiously papillose-hirsute; spikelets 3.5-3,8 mm. long, obovateelliptic, abruptly pointed, attenuate at base as in P. molle, densely hirsute to glabrous; first glume clasping, half the length of the spikelet, acute, 5-nerved; second glume and sterile lemma pointed beyond the fruit, 5-nerved, the nerves, sometimes anastomosing as in P. molle; fruit 2.9-3 mm. long, 1.5-1.6 mm. wide, obovate-elliptic, apiculate.
Type locality: Camp Lowell, Santa Cruz Valley, Arizona.
Distribution : Western Texas to southern California, and Sonora to Oaxaca.

Annuals, Terrestrial, not aquatic, Stems nodes swollen or brittle, Stems geniculate, decumbent, or lax, sometimes rooting at nodes, Stems caespitose, tufted, or clustered, Stems terete, round in cross section, or polygonal, Stems branching above base or distally at nodes, Stem nodes bearded or hairy, Stem internodes hollow, Stems with inflorescence less than 1 m tall, Stems, culms, or scapes exceeding basal leaves, Leaves mostly cauline, Leaves conspicuously 2-ranked, distichous, Leaves sheathing at base, Leaf sheath mostly open, or loose, Leaf sheath smooth, glabrous, Leaf sheath hairy, hispid or prickly, Leaf sheath and blade differentiated, Leaf blades lanceolate, Leaf blades 2-10 mm wide, Leaf blades mostly flat, Leaf blades mostly glabrous, Leaf blades more or less hairy, Ligule present, Ligule a fringed, ciliate, or lobed membrane, Inflorescence terminal, Inflorescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Inflorescence a panicle with narrowly racemose or spicate branches, Inflorescence with 2-10 branches, Inflorescence branches 1-sided, Peduncle or rachis scabrous or pubescent, often with long hairs, Rachis angular, Flowers bisexual, Spikelets pedicellate, Spikelets sessile or subsessile, Spikelets dorsally compressed or terete, Spikelet less than 3 mm wide, Spikelets with 1 fertile floret, Spikelets with 2 florets, Spikelet with 1 fertile floret and 1-2 sterile florets, Spikelets solitary at rachis nodes, Spikelets all alike and fertille, Spikelets in paired units, 1 sessile, 1 pedicellate, Spikelets bisexual, Spikelets disarticulating below the glumes, Spikelets secund, in rows on one side of rachis, Rachi lla or pedicel glabrous, Glumes present, empty bracts, Glumes 2 clearly present, Glumes distinctly unequal, Glumes equal to or longer than adjacent lemma, Glumes 4-7 nerved, Lemma coriaceous, firmer or thicker in texture than the glumes, Lemma becoming indurate, enclosing palea and caryopsis, Lemma 5-7 nerved, Lemma glabrous, Lemma rugose, with cross wrinkles, or roughened, Lemma apex acute or acuminate, Lemma awnless, Lemma straight, Palea present, well developed, Palea longer than lemma, Stamens 3, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis.