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The grass genera of the world

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

Hyparrhenia Anderss.

From the Greek hypo (under) and arrhen (male), alluding to male-only spikelets at raceme bases.

Excluding Dybowskia, Hyperthelia

Habit, vegetative morphology. Annual (rarely), or perennial (usually large); caespitose. Culms 30–300(–400) cm high; herbaceous. Culm nodes glabrous. Culm internodes solid. The shoots not aromatic. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; setaceous, or not setaceous; usually flat, or folded (sometimes); 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 (the lower spikelet pairs homogamous, the upper pairs heterogamous); hermaphrodite and male-only, or hermaphrodite and sterile; overtly heteromorphic (imperfect spikelets sometimes with awned glumes, the L2 awnless); in both homogamous and heterogamous combinations (the proximal 1–2 pairs homogamous, male or neuter). Plants inbreeding. Apomictic, or reproducing sexually.

Inflorescence. Inflorescence falsely paniculate (leafy, often with coloured spatheoles); with capillary branchlets (i.e., the articles of the racemes, and the peduncles slender); spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes ‘racemes’; paired (the racemes with a common peduncle, often deflexed, their bases terete or flattened, that of the upper usually much shorter than 9 mm by contrast with Exotheca); with very slender rachides; disarticulating; disarticulating at the joints. ‘Articles’ linear; appendaged, or not appendaged; disarticulating obliquely; densely long-hairy, or somewhat hairy, or glabrous. Spikelets paired (with terminal triplets); somewhat secund, or not secund; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite (in the upper pairs only). The ‘longer’ spikelets male-only, or sterile.

Female-sterile spikelets. The pedicelled spikelets male or sterile, without a callus, usually longer than the sessile, G1 often mucronate or aristate. L2 awnless, sometimes suppressed. The male spikelets with glumes; 1 floreted, or 2 floreted. The lemmas awnless.

Female-fertile spikelets. Spikelets 3.5–10 mm long; not noticeably compressed to compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus pointed to blunt.

Glumes two; more or less equal; long relative to the adjacent lemmas; free; not pointed (truncate); awnless; very dissimilar (the lower dorsally rounded or flattened, the upper narrower, shallowly naviculate). Lower glume not two-keeled (striate or grooved); convex on the back (rarely slightly concave or with two or more shallow depressions); not pitted; relatively smooth; 7–9 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 0 nerved, or 2 nerved; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas hyaline below, stipitate to the awn; less firm than the glumes (hyaline, but hardening into the awn); not becoming indurated; incised; 2 lobed (usually minutely bidentate); not deeply cleft; awned. Awns 1; median; from a sinus (flanked by tiny teeth); geniculate; hairy, or long-plumose; much longer than the body of the lemma. Lemmas hairy, or hairless; non-carinate; without a germination flap; 1 nerved. Palea present, or absent; when present, relatively long, or conspicuous but relatively short, or very reduced; not indurated; 2-nerved, or nerveless. Lodicules present; 2; free; fleshy, or membranous; 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 containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae over-arching the stomata; consisting of one oblique swelling per cell. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (46.5–)52–66(–72) microns long; 6–7 microns wide at the septum. Microhair total length/width at septum 6–8.5. Microhair apical cells 15–30 microns long. Microhair apical cell/total length ratio 0.33–0.55. Stomata common; 21–25.5 microns long. Subsidiaries triangular, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (a few), or not paired (mainly solitary); silicified (when paired), or not silicified. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, or butterfly shaped, or dumb-bell shaped, or nodular.

Transverse section of leaf blade, physiology. C4; biochemical type NADP–ME (H. hirta); XyMS–. PCR cells with a suberised lamella. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans (the groups of large cells (cf. Zea) or of small cells, sometimes the bulliforms irregularly grouped). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves without flavonoid sulphates (2 species).

Cytology. Chromosome base number, x = 10 and 15. 2n = 20, 30, 40, 44, 45, and 60. 2, 4, and 6 ploid. Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. About 55 species.

Distribution, phytogeography, ecology. Mediterranean, Africa, Arabia, America.

Commonly adventive. Mesophytic, or xerophytic; species of open habitats; glycophytic. Savanna.

Economic aspects. Significant weed species: H. hirta, H. rufa. Cultivated fodder: H. rufa. Important native pasture species: most more or less unpalatable, but sometimes useful, especially when young: H. anamesa, H. cymbaria, H. dregeana, H. filipendula, H. poecilotricha, etc.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia levis, Puccinia versicolor, and ‘Uromycesclignyi. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Tilletia. Ustilaginaceae — Sorosporium, Sphacelotheca, and Ustilago.

References, etc. Morphological/taxonomic: Clayton 1969. Leaf anatomical: Metcalfe 1960; studied by us - H. filipendula (Hochst.) Stapf.

Illustrations. • H. cymbaria, as Andropogon: Wood, Natal Plants 2 (1904). • H. filipendula, as Andropogon: Wood, Natal Plants 2 (1904). • H. rufa: Fl. W. Trop. Afr. (1936). • General aspect (H. hirta): Gibbs Russell et al., 1990. • Triplet of spikelets (H. hirta). • Female-fertile lemma (H. hirta). Hyparrhenia hirta. Hefty awn from the sinus of the delicate, bilobed lemma tip. • H. hirta, abaxial epidermis of leaf blade: this project. • H. hirta, abaxial epidermis of leaf blade: this project. • H. filipendula, abaxial epidermis of leaf blade: this project. • H. filipendula, abaxial epidermis of leaf blade: this project. • H. filipendula, abaxial epidermis of leaf blade: this project. • H. hirta, TS of leaf blade mid-rib: 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.’.