The grass genera of the world
Habit, vegetative morphology. Robust annual. Culms (20–)40–110 cm high; herbaceous; to to 0.3 cm in diameter; unbranched above. Culm nodes glabrous. Culm internodes solid. Plants unarmed. Young shoots intravaginal. Leaves mostly basal; non-auriculate. Sheath margins free. Leaf blades linear-lanceolate; narrow; 2–10 mm wide (to about 30 cm long); flat, or rolled; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringe of hairs; about 1 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence a false spike, with spikelets on contracted axes, or a single spike, or a single raceme (the spikelets solitary or in clusters or short secondary spikes, on the rachis of a simple or compound spike); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets secund.
Female-fertile spikelets. Spikelets 9–20 mm long; compressed laterally (becoming twisted when mature); falling with the glumes; not disarticulating between the florets (falling whole); with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Callus absent.
Glumes two; very unequal to more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; hairy (at the margins), or hairless; pointed (acute); awnless; carinate (the keel scabrid); similar (thin, membranous, ovate). Lower glume 3 nerved. Upper glume 5 nerved. Spikelets with incomplete florets. The incomplete florets both distal and proximal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets with proximal incomplete florets. The proximal incomplete florets 2; epaleate; sterile. The proximal lemmas mucronate to awned, or awnless; 6–8 nerved; less firm than the female-fertile lemmas to similar in texture to the female-fertile lemmas (intermediate in texture between glumes and fertile lemmas).
Female-fertile florets 4–20. Lemmas decidedly firmer than the glumes (cartilaginous at the base, chartaceous above, hyaline at the margins); entire; pointed; mucronate to awned (via the excurrent mid-nerve). Awns 1; median; stout, apical; hairless; much shorter than the body of the lemma. Lemmas hairy (villous along the lower margins); carinate; without a germination flap; 9–11 nerved; with the nerves non-confluent. Palea present; relatively long; apically notched; thinner than the lemma; not indurated; 2-nerved; 2-keeled. Palea keels winged (the margins and wings villous). Lodicules absent. Stamens 3. Anthers 4–5 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles fused. Stigmas 2; white.
Fruit, embryo and seedling. Fruit free from both lemma and palea (loosely enclosed); small (2 mm long); ellipsoid; compressed laterally. Hilum short. Pericarp free. Embryo large; with 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 markedly different in shape costally and intercostally (intercostals much broader); of similar wall thickness costally and intercostally (fairly thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (and pitted). Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall thinner than that of the basal cell and often collapsed to thinner than that of the basal cell but not tending to collapse. Microhairs (34.5–)36–39 microns long. Microhair basal cells 18–21 microns long. Microhairs 9.6–12 microns wide at the septum. Microhair total length/width at septum 3–4.1. Microhair apical cells 16.5–21 microns long. Microhair apical cell/total length ratio 0.42–0.56. Stomata common; 22.5–27 microns long. Subsidiaries dome-shaped to triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies present and perfectly developed; tall-and-narrow, or saddle shaped. Costal short-cells conspicuously in long rows, or predominantly paired. Costal silica bodies present in alternate cell files of the costal zones; predominantly large, broad saddle shaped.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only to interrupted both abaxially and adaxially. PCR sheath extensions absent. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (in places). Leaf blade adaxially flat (with no more than slight abaxial ribs over primary bundles). Midrib rather conspicuous (with a slight, rounded, abaxial keel); having a conventional arc of bundles (the median with a smaller lateral on either side); with colourless mesophyll adaxially, or without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these sometimes linked with traversing colourless columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries only); forming figures (in the large bundles). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Cytology. Chromosome base number, x = 10.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Eragrostideae; Unioliinae. 1 species.
Distribution, phytogeography, ecology. Angola, southwest and southern Africa.
Xerophytic (but often grows in depressions where moisture collects); species of open habitats; halophytic (sometimes), or glycophytic (usually).
References, etc. Leaf anatomical: this project; photos of E. africana provided by R.P. Ellis.
Illustrations. • E. aristulata: Gibbs Russell et al., 1990
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’.