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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Ischaemum L.

From the Greek ischaimon (a styptic), name originally given to Digitaria sanguinalis for supposed styptic qualities.

Including Argopogon Mimeur, Collardoa Cav., Ischaemopogon Griseb., Meoschium P. Beauv., Schoenanthus Adans.

Excluding Digastrium

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 10–350 cm high; herbaceous; sparsely to amply branched above, or unbranched above. The branching simple. Culm nodes hairy, or glabrous. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate, or auriculate (with sheath auricles). Leaf blades linear (usually), or linear-lanceolate to lanceolate; broad (rarely), or narrow; cordate to sagittate, or not cordate, not sagittate; flat; pseudopetiolate, or not pseudopetiolate; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and male-only (rarely), or hermaphrodite and sterile (rarely); overtly heteromorphic (the pedicelled spikelet sometimes much smaller, often asymmetric), or homomorphic.

Inflorescence. Inflorescence terminal or axillary, of spicate main branches; usually digitate. Primary inflorescence branches (1–)2(–14) (usually paired, one-sided and locked back to back to simulate a single spike). Inflorescence spatheate (the uppermost leaf reduced to a spatheate sheath), or espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’; paired, or clustered (rarely solitary); with substantial rachides (these stout, triangular); disarticulating; disarticulating at the joints. ‘Articles’ non-linear (clavate or inflated); glabrous, or more often hairy. Spikelets paired; secund (the raceme dorsiventral, its segments usually appearing U or V-shaped from the back owing to the thick internodes and pedicels); consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations, or unequally pedicellate in each combination. Pedicels of the ‘pedicellate’ spikelets free of the rachis (usually stoutly linear to obovoid, sometimes very short). The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets hermaphrodite, or male-only (rarely), or sterile (rarely).

Female-sterile spikelets. The pedicelled spikelet as large as the sessile or much reduced, variously compressed, often asymmetrical.

Female-fertile spikelets. Spikelets compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present, or absent.

Glumes two; more or less equal; long relative to the adjacent lemmas; awned (the upper, sometimes), or awnless; very dissimilar (the lower leathery and usually 2-keeled, the upper 1-keeled above and sometimes awned). Lower glume usually two-keeled (winged or not); convex on the back to concave on the back; not pitted; relatively smooth (rarely), or rugose (transversely), or tuberculate (on the margins); 7–11 nerved. Upper glume 5–11 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed. The proximal incomplete florets male. The proximal lemmas awnless; similar in texture to the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes (firmly membranous); not becoming indurated; incised; 2 lobed; awned (usually), or mucronate, or awnless (rarely). Awns when present, 1; or mucros from a sinus; geniculate; hairless (glabrous); much shorter than the body of the lemma to much longer than the body of the lemma. Lemmas hairless; non-carinate; without a germination flap; 1–5 nerved. Palea present; relatively long; apically notched; awnless, without apical setae; thinner than the lemma (hyaline); not indurated; nerveless. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit free from both lemma and palea; compressed dorsiventrally, or not noticeably compressed. Hilum short. Embryo large. Endosperm hard; without lipid; containing compound starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Seedling with a long mesocotyl.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal. Intercostal papillae over-arching the stomata (but only from the subsidiary cells); several per cell (costal and intercostal long-cells with 1–2 irregular rows of small, thick walled papillae, the subsidiaries each with a small papilla at each end). Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally (quite thin walled). Mid-intercostal long-cells rectangular and fusiform; having markedly sinuous walls. Microhairs present; more or less spherical, or elongated; ostensibly one-celled, or clearly two-celled; panicoid-type (some in I. commutatum being ‘balanoform’), or chloridoid-type; 18–48 microns long; 7.2–9.6 microns wide at the septum. Microhair total length/width at septum 1–4.4. Microhair apical cells 4–19.5 microns long. Microhair apical cell/total length ratio 0.29–0.61. Stomata common; 34.5–42 microns long. Subsidiaries papillate; predominantly triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare (ignoring the bulbous bases of short prickles). Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies ‘panicoid-type’; cross shaped, or butterfly shaped, or dumb-bell shaped, or nodular; sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines even. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms not present in discrete, regular adaxial groups (the epidermis extensively bulliform, the cells irregularly grouped). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Culm anatomy. Culm internode bundles in one or two rings.

Phytochemistry. Leaves without flavonoid sulphates (2 species).

Cytology. Chromosome base number, x = 9, or 10. 2n = 18, 20, 40, 54, 56, and 68. 2, 4, 6, and 8 ploid (?).

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Ischaeminae. 60 species.

Distribution, phytogeography, ecology. Tropical and subtropical.

Commonly adventive. Helophytic (mostly), or mesophytic, or xerophytic; shade species, or species of open habitats; halophytic, or glycophytic. Some in damp or shady places, some (e.g. I. muticum, I. triticeum) in coastal sand.

Economic aspects. Significant weed species: I. indicum, I. muticum, I. rugosum (in ricefields), I. timorense. Important native pasture species: I. muticum, I. rugosum.

Rusts and smuts. Rusts — Phakopsora and Puccinia. Taxonomically wide-ranging species: Phakopsora incompleta and Puccinia versicolor. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium, Sphacelotheca, and Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - I. fragile R. Br.

Illustrations. • I. australe: Gardner, 1952. • I. timorense: Kunth (1835). • I. latifolium: Kunth (1835). • General aspect (I. fasciculatum): Gibbs Russell et al., 1990. • I. polystachyum, as I. fasciculatum: Wood, Natal Plants 2 (1904). • I. fragile, abaxial epidermis of leaf blade: this project

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 11th December 2017.’.