The grass genera of the world
Type species: Type: O. scariosa (F.Muell.) Lazarides.
Habit, vegetative morphology. Annual, or perennial (short-lived); caespitose. Culms 15–50 cm high; herbaceous; unbranched above (5–7 noded). Culm nodes glabrous. Culm internodes solid (spongy). Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades narrow (less than 3.5 mm wide); flat, or rolled; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane (short). Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches; digitate. Primary inflorescence branches 3–6. Rachides hollowed and flattened (triqetrous). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund (the rachis dorsiventral); biseriate; subsessile to pedicellate.
Female-fertile spikelets. Spikelets 1.8–4.5 mm long (-6); compressed laterally; disarticulating above the glumes (the glumes usually persistent); not disarticulating between the florets; with distinctly elongated rachilla internodes between the florets (the sterile florets in a terminal cluster, separated from the basal floret by a thickened, elongated internode). Rachilla prolonged beyond the uppermost female-fertile floret (and modified with spongy tissue to form a conspicuous thickened internode, separating the clustered sterile florets from the basal fertile one); glabrous apart fom a few basal hairs; the rachilla extension with incomplete florets. Hairy callus present (2.5–3mm long, being elongated and pungent). Callus long; pointed.
Glumes two; very unequal; shorter than the spikelets; long relative to the adjacent lemmas; lateral to the rachis; hairless; glabrous; not pointed (G1 entire, G2 2-lobed or truncate); awnless; carinate; similar (thinly membranous to hyaline, often purple-tinged). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets (without paleas). The distal incomplete florets 3–5; clearly specialised and modified in form (the clustered sterile lemmas large, winged and awned, the lower ones broad, flaring and 7 nerved). Spikelets without proximal incomplete florets.
Female-fertile florets 1 (basal). Lemmas decidedly firmer than the glumes (cartilaginous to indurated); not becoming indurated (but dark brown when mature); incised; 2 lobed; not deeply cleft (2-toothed); awned. Awns 1; median; dorsal; from near the top; non-geniculate; hairless; about as long as the body of the lemma to much longer than the body of the lemma; entered by one vein. Lemmas hairy. The hairs in tufts (from near the apices of the lateral nerves and lower on the mid-nerve). Lemmas carinate (the mid-nerve ribbed); without a germination flap; 3 nerved (the laterals submarginal); with the nerves confluent towards the tip. Palea present; relatively long; apically notched; awnless, without apical setae; not indurated (membranous); 2-nerved; 2-keeled. Palea keels winged (the wings ciliate). Lodicules absent. Stamens 3. Anthers very small; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (1.3–2 mm long); trigonous. Hilum short. Pericarp fused. Embryo large (almost as long as the fruit). Endosperm hard.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae over-arching the stomata; consisting of one symmetrical projection per cell (mostly). Long-cells markedly different in shape costally and intercostally (the non-papillate costals narrower and more regular). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 22.5–24–27 microns long. Microhair basal cells 12 microns long. Microhairs 9.6–12–15 microns wide at the septum. Microhair total length/width at septum 1.8–2.5. Microhair apical cells (9–)10.5–12(–13.5) microns long. Microhair apical cell/total length ratio 0.33–0.56. Stomata common; 16.5–19.5 microns long. Subsidiaries dome-shaped and triangular. Intercostal short-cells common; not paired (solitary); not silicified. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; exclusively saddle shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; biochemical type NADME (1 species); XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions present. Maximum number of extension cells 1. PCR cells without a suberised lamella. PCR cell chloroplasts elongated; with well developed grana; centripetal. Leaf blade nodular in section; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (seemingly, in the poor material seen). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Phytochemistry. Leaf blade chlorophyll a:b ratio 3.88–4.5.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Eleusininae. 1 species (O. scariosa).
Distribution, phytogeography, ecology. Australia.
Xerophytic; species of open habitats; halophytic to glycophytic. Dry savanna.
References, etc. Morphological/taxonomic: Lazarides 1985. Leaf anatomical: studied by us.
Illustrations. • Inflorescence, spikelet details (O. scariosa): E. Hickman, in Lazarides (1985). • Spikelet of O. scariosa. • O. scariosa, abaxial epidermis of leaf blade: this project
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. delta-intkey.com/grass’.