Grass Genera of the World

L. Watson and M. J. Dallwitz


Hymenachne P. Beauv.

From the Greek hymen (a membrane) and achne (chaff), alluding to membranous glumes, lemmas and paleas.

Habit, vegetative morphology. Perennial; decumbent aquatics. Culms 50–200 cm high; herbaceous. Culm nodes glabrous. Culm internodes solid (but aerenchymatous). Leaves not basally aggregated; non-auriculate. Leaf blades linear to lanceolate; broad, or narrow; cordate, or not cordate, not sagittate; not pseudopetiolate; cross veined, or without cross venation; persistent; ligule present; an unfringed membrane.

Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality.

Inflorescence. Inflorescence of spicate main branches, or paniculate (spiciform or contracted, often with appressed branches). Primary inflorescence branches inserted all around the main axis. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund. Pedicel apices truncate, or discoid.

Female-fertile spikelets. Spikelets narrowly lanceolate; abaxial; not noticeably compressed to compressed dorsiventrally; falling with the glumes; with a distinctly elongated rachilla internode between the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes present; two; very unequal; (the upper) shorter than the spikelets to about equalling the spikelets (G1 about half as long); shorter than the adjacent lemmas to long relative to the adjacent lemmas; free (widely separated); awnless; similar (hyaline, not gibbous). Lower glume about 0.5 times the length of the upper glume; 1–3 nerved. Upper glume 3–7 nerved (usually acuminate). 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 acute, acuminate or awnlike; more or less awned, or awnless; 3–5 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas to similar in texture to the female-fertile lemmas (hyaline, lanceolate, acuminate); not becoming indurated.

Female-fertile florets 1. Lemmas similar in texture to the glumes to decidedly firmer than the glumes (membranous to leathery); smooth; not becoming indurated; white in fruit; entire; pointed; awnless; hairless; non-carinate; having the margins lying flat on the palea (except at the base); without a germination flap; 2 nerved, or 3 nerved. Palea present; relatively long; gaping; entire; awnless, without apical setae; textured like the lemma; not indurated. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary glabrous; without a conspicuous apical appendage. Styles fused. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed dorsiventrally. Hilum short. Embryo large; waisted.

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. Mid-intercostal long-cells rectangular to fusiform; having markedly sinuous walls. Microhairs present; more or less chloridoid-type (though the apical cells fairly thin walled); 27–36 microns long; 7.5–9 microns wide at the septum. Microhair total length/width at septum 2–4.3. Microhair apical cells (12–)13.5–15(–18) microns long. Microhair apical cell/total length ratio 0.44–0.54. Stomata common; 30–34.5 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs, or not paired (solitary); silicified (when paired), or not silicified. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles (a small lateral on each side). Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. 2n = 24.

Taxonomy. Panicoideae; Panicodae; Paniceae.

Distribution, ecology, phytogeography. 5 species; tropical. Hydrophytic to helophytic (in swamps); glycophytic.

Paleotropical, Neotropical, and Australian. Indomalesian. Indian, Indo-Chinese, Malesian, and Papuan. Caribbean, Venezuela and Surinam, Amazon, Central Brazilian, Pampas, and Andean. North and East Australian. Tropical North and East Australian.

Economic importance. Important native pasture species: H. acutigluma, in swamps.

References, etc. Leaf anatomical: this project.

Illustrations. • Abaxial epidermis of leaf blade. • Abaxial epidermis of leaf blade


Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).

Index