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The grass genera of the world

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

Hackelochloa Kuntze

Named for agrostologist Eduard Hackel, plus Greek chloa (grass).

~ Mnesithea

Including Rytilix Rafin.

Habit, vegetative morphology. Annual; caespitose. Culms (5–)30–100 cm high; herbaceous; branched above. The branching simple, or fastigiate. Culm nodes hairy, or glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades linear-lanceolate; broad, or narrow; up to 10–15 mm wide; flat; without cross venation; persistent. Ligule a fringed 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 (the pairs sometimes homogamous); hermaphrodite, or hermaphrodite and male-only, or hermaphrodite, male-only, and sterile. The male and female-fertile spikelets mixed in the inflorescence. The spikelets overtly heteromorphic (the pedicellate spikelets narrowly ovate and winged, herbaceous); in both homogamous and heterogamous combinations, or all in heterogamous combinations.

Inflorescence. Inflorescence paniculate (the numerous ‘racemes’ solitary in their spathes, usually in fascicles). Rachides hollowed. Inflorescence spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes spikelike; solitary (in their spathes); with substantial rachides; disarticulating; disarticulating at the joints (the sessile spikelets falling with the joint and the pedicelled spikelet). ‘Articles’ non-linear (grooved, concave); with a basal callus-knob; disarticulating obliquely; glabrous. Spikelets paired; secund (the sessile members in two alternating rows, on one side of the rachis); consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets discernible, but fused with the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets hermaphrodite (the glumes herbaceous and similar, the lower lemma present or absent), or male-only, or sterile.

Female-sterile spikelets. The pedicellate spikelets sometimes male-only or sterile.

Female-fertile spikelets. Spikelets 1–3 mm long; abaxial; compressed dorsiventrally (to globose); falling with the glumes. Rachilla terminated by a female-fertile floret.

Glumes two; relatively large; not greatly different in length, but G2 hooded by G1; long relative to the adjacent lemmas; awnless; very dissimilar (the lower cartilaginous, globose, reticulate-pitted, the upper thinner and embedded in the axis). Lower glume not two-keeled; convex on the back; lacunose with deep depressions; 7–10 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; decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas ovate-obtuse; less firm than the glumes (hyaline, flimsy); not becoming indurated; entire; blunt; awnless; hairless; non-carinate; without a germination flap; 0 nerved. Palea present, or absent; when present, relatively long, or conspicuous but relatively short, or very reduced; entire; awnless, without apical setae; not indurated (hyaline); nerveless (hyaline, flimsy). Lodicules present; fleshy. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit compressed dorsiventrally. Hilum short. Embryo large; 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 absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (fairly thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 43.5–54 microns long; 4.5–7.5 microns wide at the septum. Microhair total length/width at septum 6.4–10.3. Microhair apical cells 21–34.5 microns long. Microhair apical cell/total length ratio 0.44–0.72. Stomata common; 24–39 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies cross-shaped. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’.

Transverse section of leaf blade, physiology. C4; XyMS–. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles (rarely). Bulliforms present in discrete, regular adaxial groups (and also in irregular groups); in simple fans (some of these of the large celled, Zea-type). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. Lower glume of female-fertile spikelet globose, pitted.

Cytology. Chromosome base number, x = 7 (?). 2n = 14 (?). 2 ploid.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. 2 species.

Distribution, phytogeography, ecology. Tropics, southern China and southern U.S.A.

Helophytic to mesophytic; species of open habitats; glycophytic. Grassland and disturbed ground.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia levis. Smuts from Ustilaginaceae. Ustilaginaceae — Sphacelotheca.

References, etc. Leaf anatomical: studied by us - H. granularis (L.) Kuntze.

Illustrations. • H. granularis: Gardner, 1952. • General aspect (H. granularis): Gibbs Russell et al., 1990. • Inflorescence detail (H. granularis). • Inflorescence detail (H. granularis). Hackelochloa granularis.

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.’.