Digitaire Filiforme

Digitaria ischaemum is very close to D. violascens, but has a slightly stouter habit with broader leaves, a few short, widely spreading racemes, and larger, plumper spikelets. It also has a more temperate distribution.

Digitaria ischaemum, D. fauriei, D. longiflora, and D. violascens belong to a group of Digitaria known as the Verrucipilae because of their warty spikelet hairs. A compound microscope is required to see this, but the hairs have a beadlike appearance under moderate magnification. These spikelet hairs also have curled tips in D. ischaemum (and sometimes in D. violascens), which led to the hairs being described as capitate or clavate in the past.

Digitaria ischaemum is much more closely related to Digitaria violascens than has hitherto been supposed. Henrard placed it in his section Clavipilae, along with Digitaria stricta, but close examination of the hairs has shown that they are not in fact clavate Although they appear, under moderate magnification, to have a clavate tip, this is not due to a swelling, but to a curious crozier-like curling of the tip of the hair itself. Furthermore, when viewed under higher magnification (preferably through a compound microscope), the hairs can be seen to be verrucose. Apart from geographical distribution, the main distinctions between Digitaria ischaemum and Digitaria violascens lie in the larger spikelets of Digitaria ischaemum and its longer, matted, pseudo-clavate hairs.

Annuals; culms tufted, erect or ascending, 30-60 cm high. Sheaths loose, keeled, usually shorter than internode; ligule membranaceous, ca. 2 mm long; blade 2-10 cm long, 2-5 mm wide, leaf-base rounded. Racemes 2-5, 1-20 cm long, digitately arranged; rachis 0.8-1.2 mm wide, indurate, margins scabrous, green; midrib white, narrow, each node with 2-3 spikelets. Spikelets elliptic, 1.5-2.3 mm long, greyish green or purplish; lower glume minute or absent, translucently membranaceous, veinless; upper glume equaling spikelet or slightly shorter, narrow, 3-veined, interveins and margins coverd with soft clavate hairs; lower lemma 5-veined, interveins and margins also clavate hairs; upper floret coriaceous, blackish brown when mature, equaling spikelet. Caryopsis ca. 1.2 mm long.

Annual, whole plant often purple-tinged. Culms loosely tufted, erect or ascending, 15–40 cm tall. Leaf sheaths loose, usually keeled, glabrous or pilose; leaf blades linear-lanceolate, 5–12 × 0.4–0.8 cm, ± pilose, base subrounded, apex acuminate; ligule ca. 0.6 mm. Inflorescence digitate or on a short axis; racemes 2–4, divaricate, 2–9 cm; spikelets ternate; rachis ribbonlike, winged, 0.8–1.1 mm broad, midrib white, rounded or triquetrous, narrower than the green or purple wings, margins serrulate; pedicels angular, scabrous, tips discoid. Spikelets elliptic, 2–2.2 mm, pilose with verrucose hairs, some with curled tips; lower glume absent or a tiny hyaline rim; upper glume as long as spikelet or slightly shorter, 3–5-veined, intervein spaces and margins appressed-pilose; lower lemma as long as spikelet, 5–7-veined, interveins and margins appressed-pilose; upper lemma purplish brown to blackish at maturity. Fl. and fr. Jun–Nov. 2n = 36.

Annual; culms (10-)1540 cm high, erect or geniculately ascending. Leaf-blades 2.5-11 cm long, 3.5-8 mm wide. Inflorescence composed of 2-4(-6) racemes; racemes 2.5-8(11) cm long, subdigitate or arranged along an axis 1.5-2(4) cm long, the spikelets ternate on a ribbon-like winged rhachis with rounded or triquetrous midrib; pedicels terete to flattened and winged, scabrid, with discoid or cupuliform tip. Spikelets elliptic or lanceolate, 1.9-2.4 mm long; lower glume an obscure hyaline rim; upper glume almost as long as the spikelet, 5-nerved, with matted verrucose hairs between the nerves; lower lemma as long as the spikelet, 7-nerved, pubescent with matted verrucose hairs; fruit ellipsoid, dark brown to almost black.

The temperate regions of the world. Taiwan, in open waste places of the northeastern part.

Distribution: Pakistan (N.W.F.P., Gilgit & Kashmir); North America; Europe extending eastwards into northern Asia.

Other, unlocalised, records are Kashmir, J.L. Stewart 850b(K) and Gilgit, R.R. Stewart 26652(K).

Fl. & Fr. Per.: July-August.

Open grassy places. Anhui, Fujian, Gansu, Hebei, Heilongjiang, Henan, Jiangsu, Jilin, Liaoning, Nei Mongol, Ningxia, Shaanxi, Shandong, Shanxi, Sichuan, Taiwan, Xinjiang, Xizang [Japan, Pakistan, Russia; Europe, North America].

Panicum ischaemum Schreb., Spec. Fl. Erlang. 16. 1804.

Panicum ischaemum Schreber in Schweigger, Spec. Fl. Erlang. 16. 1804; Digitaria asiatica (Ohwi) Tzvelev; D. humi-fusa Persoon; D. ischaemum subsp. asiatica (Ohwi) Tzvelev; D. ischaemum var. asiatica Ohwi; Panicum humifusum (Persoon) Kunth; Paspalum humifusum (Persoon) Poiret; Syntheris-ma humifusa (Persoon) Rydberg.

Syntherisma ischaemum (Schreb.) Nash
Panicum lineare Krock. Fl. Sil. 1 : 95. 1787.. Not P, lineare L. 1762. Panicum Ischaemum Schreb.; Schweigger, Spec, Fl. Brlaug. 16. 1804. Digttaria humifusa Pers. Syn. PI. 1 : 85. 1805. Paspalum amhigutim DC. Fl. Fr. 3 : 16. 1805.
Syntherisma glabrum Schrad. Fl. Germ. 163. 1806.
Panicum glabrum. Gaudin, Agrost. Helv. 1 : 22. 1811.
Panicwm glabrum m-tssissippiense Gatt. Tenn. Fl. 95. 1887.
Synlherisma lineare Nash, Bull. Torrey Club 22 : 420. 1895.
Panicum. lineare m.ississippiense Gatt.; Beal, Grasses N. Am. 2 : 111, 1896.
Syntherism.a lineare mississippiense Nash, Bull, Torrey Club 25: 300. 1898.
Synlherisma humifusum Rydb. Mem. N. Y. Bot. Gard. 1 : 469, 1900.
Stems 2-5 dm. tall, slender, at length branched at the base, finally prostrate and forming large mats, smooth and glabrous; leaf-sheaths flattened, smooth, glabrous; blades up to 1.5 dm. long, 2.5-6 mm. wide, flat, erect or nearly so; panicle finally long-exserted, the axis 1-3 cm. long; racemes 2-5, 2-8 cm. long, finally widely spreading; spikelets slightly exceeding 2 mm. long, elliptic, acutish, on 3-angled pedicels which are sparingly or not at all hispid at the apex, usually in pairs, the outer scales usually purplish or purple, the first scale wanting, or sometimes present as a scarious rudiment, the second and third scales about equal, pubescent, the second 3-nerved, the third 7-nerved, the fruiting scale deep chestnut-brown when mature, striate, acute.
Type locality: Krlangen, Germany.
Distribution : Nova Scotia to Ontario, South Dakota, and Colorado, and south to Florida and Texas. Introduced,

Annuals, Terrestrial, not aquatic, Stems trailing, spreading or prostrate, Stems nodes swollen or brittle, Stems geniculate, decumbent, or lax, sometimes rooting at nodes, Stems mat or turf forming, Stems caespitose, tufted, or clustered, Stems terete, round in cross section, or polygonal, 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 linear, Leaf blades 2-10 mm wide, Leaf blades mostly flat, Leaf blades mostly glabrous, Ligule pr esent, Ligule an unfringed eciliate membrane, Inflorescence terminal, Inflorescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Inflorescence a panicle with digitately arranged spicate branches, Inflorescence with 2-10 branches, Inflorescence branches 1-sided, Lower panicle branches whorled, Rachis winged, Rachis angular, Flowers bisexual, Spikelets pedicellate, 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 3 per node, Spikelets all alike and fertille, Spikelets bisexual, Spikelets disarticulating below the glumes, Spikelets secund, in rows on one side of rachis, Rachilla or pedicel glabrous, Glumes present, empty bracts, Glumes 1 clearly present, the other greatly reduced or absent, Glumes 2 clearly present, Glumes distinctly unequal, Glumes equal to or longer than adjacent lemma, Glume equa l to or longer than spikelet, Glume surface hairy, villous or pilose, Glumes 3 nerved, Lemmas thin, chartaceous, hyaline, cartilaginous, or membranous, Lemma similar in texture to glumes, Lemma 5-7 nerved, Lemma apex acute or acuminate, Lemma awnless, Lemma margins thin, lying flat, Lemma straight, Palea present, well developed, Palea membranous, hyaline, Palea about equal to lemma, Stamens 3, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis, Caryopsis ellipsoid, longitudinally grooved, hilum long-linear.

Digitaria ischaemum is a species of crabgrass known by the common names smooth crabgrass and small crabgrass. It is native to Europe and Asia, but it is known throughout much of the warm temperate world as an introduced species and often a common roadside and garden weed. It is an annual grass producing an inflorescence with two or more narrow branches lined with tiny spikelets.

It is easily confused with other members in the genus, particularly southern crabgrass in California which differs by having spikelets of nearly twice the length. It may also be confused with Bermuda Grass, but differs in being a much taller plant with a much longer inflorescence. The leaves on this grass often form above the base of the plant, and it is usually singular, rarely forming large clumps.