Aristida adscensionis L.

Nile region, oases, Egyptian desert, Res Sea coastal strip, Gebel Elba and Sinai (St.Katherine).

Throughout the tropics and subtropics.

Ubiquitous weed.

Annual.

Aristida adscensionis is a widely distributed, variable, annual pioneer of dry, open places, recognized by its long, parallel-sided, flattened lemma often exserted from the glumes. It is used for forage.

Aristida adscensionis is a pan-tropical weed and morphologically extremely variable. There are no discontinuities between var. adscensionis and either var. pumila or var. ehrenbergii and the distinctions between them are hardly worth maintaining. The same may be said of Aristida depressa, an extreme form completely intergrading with Aristida adscensionis. The distinction between annuals and perennials in the tropics and subtropics is not always very clear and often appears to be a facultative difference of little taxonomic consequence. This is particularly true in Aristida adscensionis where the separation of perennial plants as Aristida caerulescens cannot be justified. Indeed, perennial plants, otherwise indistinguishable from typical var. ehrenbergii are seen in the Middle East.

Six-weeks Tripleawn (a North American name) is probably grazed by cattle, but nothing more definite about its economic value in Pakistan seems to be known.

Annual. Culms tufted, erect or geniculate at base, 15–55 cm tall, branched. Leaf sheaths smooth, glabrous, shorter than internodes, laxly overlapping; leaf blades involute, 3–20 cm, finely pointed; ligule ca. 0.5 mm. Panicle usually narrow, loosely contracted, 4–20 cm; branches short, ascending, inserted singly on main axis. Spikelets gray-green or purplish green; glumes subequal or unequal with upper longer, 1-veined, scabrid on vein, lower glume lanceolate-oblong, 4–6.8 mm, acute, upper glume linear, 5–8 mm, obtuse to emarginate or apiculate; callus ca. 0.5 mm, narrowly obtuse; lemma linear, distinctly longer than upper glume, 7–11 mm, laterally compressed, smooth or rarely scabrid in upper half, keel scabrid upward; awn branches arising directly from lemma apex, central branch 1–2.5 cm, laterals slightly shorter. Anthers 1.8–2 mm. Fl. and fr. Jun–Oct.

Annual or short-lived perennial, forming erect or sprawling tufts 10-100 cm high. Leaf-blades linear, up to 20 cm long and 3 mm wide, expanded or folded. Panicle up to 30 cm long, occasionally lax, usually ± contracted about the main branches, sometimes narrow and dense. Spikelets pallid, green or purple; glumes unequal, linear-lanceolate to lanceolate, scaberulous on the keel, emarginate and mucronate or acute but never awned, the upper 5-10 mm long, the lower 1-3 mm shorter; lemma 5-13(17) mm long, sometimes no longer than the glumes but usually exceeding the upper by 1-2 mm or more, laterally compressed, convolute, scabrid on the keel or sometimes generally scaberulous on the upper part, passing into the awn without constriction or articulation; callus narrowly oblong, 0.5 mm long, obtuse; central branch of the awn 7-25 mm long, the laterals subequal or occasionally conspicuously shorter.

Widely distributed in Old & New Worlds.

Distribution: Pakistan (Sind, Baluchistan, Punjab, N.W.F.P., Gilgit & Kashmir); throughout the tropics.

Gansu, Hebei, Nei Mongol, Qinghai, Shaanxi, Shandong, Shanxi, Sichuan, Xinjiang, Yunnan [tropical and warm-temperate regions of the world].

2000 m

Fl. & Fr. Per.: March-December.

Dry mountain slopes, rocky fissures, and along river banks; 200–1800 m.

Aristida adscensionis var. vulpioides (Hance) Hackel ex Henrard; A. heymannii Regel; A. vulgaris Trinius & Ruprecht; A. vulpioides Hance; Chaetaria adscensionis (Linnaeus) P. Beauvois.

Annuals, Terrestrial, not aquatic, Rhizomes present, Rhizome short and compact, stems close, Stems nodes swollen or brittle, Stems erect or ascending, Stems caespitose, tufted, or clustered, Stems terete, round in cross section, or polygonal, Stems branching above base or distally at nodes, Stem internodes solid or spongy, 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 and blade differentiated, Leaf blades linear, Leaf blades very narrow or filiform, less than 2 mm wide, Leaf blades 2-10 mm wide, Leaf blades mostly flat, Leaf blade margins folded, involute, or conduplicate, Leaf blades mostly glabrous, Leaf blades more or less hairy, Ligul e present, Ligule a fringe of hairs, Inflorescence terminal, Inflorescence an open panicle, openly paniculate, branches spreading, Inflorescence a contracted panicle, narrowly paniculate, branches appressed or ascending, Inflorescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Inflorescence with 2-10 branches, Flowers bisexual, Spikelets pedicellate, Spikelets laterally compressed, Spikelet less than 3 mm wide, Spikelets with 1 fertile floret, Spikelets solitary at rachis nodes, Spikelets all alike and fertille, Spikelets bisexual, Spikelets disarticulating above the glumes, glumes persistent, Spikelets disarticulating beneath or between the florets, Rachilla or pedicel glabrous, Glumes present, empty bracts, Glumes 2 clearly present, Glumes distinctly unequal, Glumes shorter than adjacent lemma, Glumes equal to or longer than adjacent lemma, Glumes 1 nerved, Lemma coriaceous, firmer or thicker in texture than the glumes, Lemma 3 nerved, Lemma glabrous, Lemma apex acute or acuminate, Lemma distinctly awned, more than 2-3 mm, Lemma with 3 awns, Lemma awns about equal in length, Lemma awn 1-2 cm long, Lemma awn 2-4 cm long or longer, Lemma awned from tip, Lemma awns straight or curved to base, Lemma awn once geniculate, bent once, Lemma margins inrolled, tightly covering palea and caryopsis, Lemma straight, Callus or base of lemma evidently hairy, Callus hairs shorter than lemma, Palea present, well developed, Palea membranous, hyaline, Palea shorter than lemma, Palea 2 nerved or 2 keeled, Stamens 3, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis, Caryopsis ellipsoid, longitudinally grooved, hilum long-linear.

Aristida adscensionis is a species of grass known by the common name sixweeks threeawn. It is native to the Americas but it is distributed nearly worldwide. It grows easily in disturbed and waste areas and has potential to become a weed.