The grass genera of the world
Habit, vegetative morphology. Perennial; densely caespitose. Culms 30–90 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes solid. Plants unarmed. Young shoots intravaginal. Leaves mostly basal; non-auriculate (but with auricular hairs). The basal sheaths persistent, keeled. Leaf blades stiffly linear; narrow; 1–4 mm wide (by 7–25 cm long); flat, or rolled; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane; truncate; 0.2–0.3 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence a single spike (very rarely two); usually non-digitate. Inflorescence axes not ending in spikelets (conspicuously bare-tipped). Rachides hollowed and flattened (crescentic in section, the edges ciliate). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund; alternately biseriate (along the midrib of the rachis); very densely imbricate.
Female-fertile spikelets. Spikelets 6–7 mm long (darkly pigmented); adaxial; compressed laterally; disarticulating above the glumes; not disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus absent. Callus absent.
Glumes two (dark grey-green); very unequal (G2 much larger); about equalling the spikelets (i.e. the upper glumes); (the upper) long relative to the adjacent lemmas; lateral to the rachis; hairless (G2 keels scabrid); glabrous; without conspicuous tufts or rows of hairs; pointed; awnless; carinate (G1), or non-carinate (the G2 being 2-keeled); very dissimilar (the G1 smaller, 1-keeled, thinner, the G2 2-keeled, firm). Lower glume 1 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets (the second and third male, the fourth if present sterile, these all enclosed in the lemma of the lower male floret and not exceeding the L1). The distal incomplete florets 2–3; merely underdeveloped; awnless. Spikelets without proximal incomplete florets.
Female-fertile florets 1. Lemmas similar in texture to the glumes (firmly membranous); not becoming indurated (membranous to papery, grey); entire; blunt; awnless; hairy (the L1 being long-ciliate on its keel and margins); carinate (folded); without a germination flap; 3 nerved; with the nerves non-confluent. Palea present (hairy near its tip); relatively long; slightly apically notched; awnless, without apical setae; textured like the lemma; not indurated (membranous); 2-nerved; 2-keeled. Palea keels slightly winged; glabrous. Lodicules present; free; fleshy (winged); glabrous; not or scarcely vascularized. Stamens 3 (in hermaphrodite and male florets). Anthers to 2.5 mm long (larger than in the male florets); not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; brown.
Fruit, embryo and seedling. Fruit free from both lemma and palea (but embraced); small (3 mm long); ellipsoid; obtusely triquetrous. Hilum short. Pericarp fused. Embryo large.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal. Intercostal papillae over-arching the stomata; consisting of one symmetrical projection per cell (long-cells and interstomatals mostly each with one large, tall, thick-walled cylindrical papilla). Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (walls thick, pitted). Intercostal zones with typical long-cells (though these rather short). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical; ostensibly one-celled; chloridoid-type. Stomata common. Subsidiaries triangular (detectable despite the papillae). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (solitary). Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies confined to the central file(s) of the costal zones; saddle shaped.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4. The anatomical organization somewhat unconventional. Organization of PCR tissue almost Triodia type (though no linking across adjacent PCR sheaths seen). XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions absent. PCR cell chloroplasts centripetal. Mesophyll perhaps with arm cells (?). Leaf blade adaxially flat (except over the midrib, but with deep abaxial clefts between the bundles). Midrib conspicuous (by its position, and its small adaxial ribs); having a conventional arc of bundles; with colourless mesophyll adaxially (the entire adaxial two-thirds of the blade comprising colourless tissue of large (apparently lignified) cells, which broadly truncates the PCR sheaths). Bulliforms not present in discrete, regular adaxial groups (no bulliforms seen). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (all bundles with abaxial girders only). Sclerenchyma not all bundle-associated. The extra sclerenchyma in adaxial groups (there being an irregularly discontinuous adaxial hypodermis of thick-walled fibres).
Cytology. Chromosome base number, x = 10. 2n = 40.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae. 1 species.
Distribution, phytogeography, ecology. Southern Africa.
Mesophytic; species of open habitats; glycophytic. Grassland.
References, etc. Leaf anatomical: this project; photos provided by R.P. Ellis.
Illustrations. • General aspect (H. fallax): Gibbs Russell et al., 1990. • Abaxial epidermis of leaf blade (H. fallax)
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’.