The grass genera of the world
Habit, vegetative morphology. Annual, or perennial; rooting at the nodes and then erect, rarely caespitose (H. longispicula). Culms 15–120 cm high; herbaceous; scandent, or not scandent; sparsely branched above, or unbranched above. The branching simple. Culm nodes glabrous. Culm internodes hollow. Plants unarmed. Leaves mostly basal (H. longispicula), or not basally aggregated; auriculate (the auricles small, on the sheath). The sheath margins with stiff hairs. Leaf blades linear (in H. longispicula), or linear-lanceolate to ovate-lanceolate (usually, and acuminate); broad (usually), or narrow (in H. longispicula); cordate (usually), or not cordate, not sagittate (H. longispicula); pseudopetiolate (usually), or not pseudopetiolate (H. longispicula); without cross venation; seemingly persistent. Ligule present; an unfringed membrane (H. glutinosa), or a fringed membrane (H. isocalycina), or a fringe of hairs (H. longispicula). Contra-ligule present (H. aturensis), or absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open; with capillary branchlets; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; not in distinct long-and-short combinations.
Female-fertile spikelets. Spikelets 2.7–11 mm long; lanceolate; compressed dorsiventrally; falling with the glumes; with conventional internode spacings to with a distinctly elongated rachilla internode between the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas; sparsely hairy, or hairless; pointed; awnless; non-carinate; similar. Lower glume 5–9 nerved. Upper glume 7–9 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 (membranous). The proximal incomplete florets male, or sterile. The proximal lemmas awnless; 5–7 nerved (with dense long stiff white hairs on the back, the folded margins enclosing the L2 in palea-like fashion); decidedly exceeding the female-fertile lemmas; ultimately less firm than the female-fertile lemmas; not becoming indurated.
Female-fertile florets 1. Lemmas decidedly firmer than the glumes (ultimately); smooth; becoming indurated (cartilaginous); awnless; hairless; non-carinate; having the margins lying flat on the palea; with a clear germination flap; 5 nerved. Palea present; relatively long; entire (pointed); awnless, without apical setae; thinly cartilaginous, with hyaline infolded margins above; 2-nerved; keel-less. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles basally fused, or free to their bases. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit small; compressed dorsiventrally. Hilum long-linear. Embryo large; without an epiblast; with a scutellar tail; with an elongated mesocotyl internode; with more than one scutellum bundle (3). Embryonic leaf margins overlapping.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type (but the distal cells large and fat); (52–)54–69(–70.5) microns long, or 36–42 microns long (in H. longispicula); (6.6–)7.5–12(–13.5) microns wide at the septum. Microhair total length/width at septum 5.5–9.3, or 3.1–3.6 (H. longispicula). Microhair apical cells (30–)33–39(–41) microns long, or 18–24 microns long (H. longispicula). Microhair apical cell/total length ratio 0.5–0.7. Stomata common; 27–43.5 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Costal short-cells conspicuously in long rows (e.g., H. aturensis), or predominantly paired (H. glutinosum, H. longispicula), or conspicuously in long rows and neither distinctly grouped into long rows nor predominantly paired (H. isocalycia). Costal silica bodies basically panicoid-type, or tall-and-narrow to crescentic (intergrading with narrow crosses); mainly cross shaped, dumb-bell shaped, and nodular.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade; with fusoids (these very large and regular in H. aturensis, H. isocalycia, H. glutinosum), or without fusoids (H. longispicula). The fusoids external to the PBS (contiguous with laterally extended PBS cells). Leaf blade nodular in section to adaxially flat; when present, with the ribs more or less constant in size (broad, low). Midrib conspicuous (by virtue of its large bundle, with heavier abaxial sclerenchyma); with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (the groups large). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming figures (in the primaries, but the sclerenchyma masses small except in H. longispicula). Sclerenchyma all associated with vascular bundles.
Cytology. 2n = 22, 24, and 40.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae; Arthropogoninae. 4 species.
Distribution, phytogeography, ecology. Tropical South America.
Helophytic to mesophytic; shade species and species of open habitats; glycophytic. In moist woods and wet places.
References, etc. Leaf anatomical: this project.
Illustrations. • H. aturensis, spikelets: Chase, Notes on Paniceae (1906)
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: 13th November 2017. delta-intkey.com/grass’.