The grass genera of the world
Type species: Type: A. avenaceus R. Br.
Habit, vegetative morphology. Oat-like perennial; caespitose. Culms 60–110 cm high; herbaceous. Culm nodes glabrous. Culm internodes hollow. Leaves mostly basal; non-auriculate. Leaf blades linear-lanceolate; narrow; 2–3 mm wide; flat to rolled; not pseudopetiolate; without cross venation; persistent. Ligule a fringed membrane (the membrane short to relatively long, hairy on the back). Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence few spikeleted (the spikelets large); paniculate; open; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 40–60 mm long; compressed laterally; disarticulating above the glumes. Rachilla usually prolonged beyond the uppermost female-fertile floret (the slender prolongation 6–8 mm long, in the palea groove), or terminated by a female-fertile floret; the rachilla extension (when present) with incomplete florets. Hairy callus present. The callus hairs white (dense). Callus long (about 6 mm long); pointed.
Glumes two; relatively large; more or less equal (the upper slightly longer); exceeding the spikelets; long relative to the adjacent lemmas; pointed (lanceolate, attenuate); awnless; non-carinate; similar (3–5 cm long, rather flat and leafy). Lower glume 7–9 nerved. Upper glume 7–9 nerved. Spikelets with female-fertile florets only, or with incomplete florets (usually with a single, abortive floret). The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped (minute).
Female-fertile florets 1. Lemmas decidedly firmer than the glumes; not becoming indurated (but very firmly leathery); incised; 3 lobed; awned. Awns 3; median and lateral; the median different in form from the laterals; from a sinus; geniculate; hairless to hairy; much longer than the body of the lemma (up to 8 cm long); entered by several veins (5); persistent. The lateral awns shorter than the median (15–25 mm long, straight to twisted but non-geniculate, relatively slender). Lemmas hairy (with dense, white hairs); non-carinate (rounded on the back); without a germination flap; 3 nerved. Palea present; relatively long; not prow-tipped; apically notched; awnless, without apical setae; textured like the lemma; firm, except for the membranous, bifid tip; 2-nerved; 2-keeled (the keels closely apposed below, diverging towards the tip). Palea keels wingless. Lodicules present; 3; free; membranous (two stipoid and larger, the third smaller and flimsier); glabrous; not toothed; not or scarcely vascularized. Stamens 3. Anthers 10–14 mm long; not penicillate; without an apically prolonged connective. Ovary apically hairy (sparingly so, towards the apex). Styles free to their bases. Stigmas 2, or 3; white.
Fruit, embryo and seedling. Fruit medium sized; not noticeably compressed. Hilum long-linear. Pericarp free, or loosely adherent. Embryo small; waisted. Endosperm containing compound starch grains.
Ovule, embryology. Micropyle oblique. Outer integument covering no more than the chalazal half of the ovule; more than two cells thick at the micropylar margin. Inner integument continuous, the micropyle constricted; thickened around the micropyle. Synergids not haustorial; without large, globular starch grains.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (or the costals narrower); of similar wall thickness costally and intercostally (or the costals somewhat thicker-walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls and having straight or only gently undulating walls (conspicuously pitted). Microhairs absent. Stomata absent or very rare; 18–27 microns long. Guard-cells overlapping to flush with the interstomatals (i.e., in the few seen). Intercostal short-cells common; in cork/silica-cell pairs. Heavily pitted prickle bases abundant. Crown cells absent. Costal short-cells varying in arrangement from file to file, conspicuously in long rows, or predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies panicoid-type (mostly), or tall-and-narrow (a few); predominantly short dumb-bell shaped.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes (small, round-topped ribs alternating with large, flat-topped ones). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (one group in each furrow); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (most bundles with a conspicuous I). Sclerenchyma not all bundle-associated. The extra sclerenchyma in abaxial groups, or in a continuous abaxial layer.
Classification. Watson & Dallwitz (1994): Stipoideae; Anisopogoneae. Soreng et al. (2015): Pooideae; Phaenospermateae. 1 species (A. avenaceus).
Distribution, phytogeography, ecology. Australia.
Xerophytic; species of open habitats; glycophytic. Light Eucalyptus forest and heathland.
References, etc. Leaf anatomical: this project.
Special comments. An isolated monotypic, seeming nearest to Stipeae; but the taxonomic relationships of Anisopogon have yet to be convincingly determined, despite the broad scope and good quality of the available descriptive data. A prime candidate for comparative DNA studies. Illustrations. • A. avenaceus: Kunth (1835), Dist. méthodique de la famille Graminées. • Ligule of A. avenaceus. • Flower with lodicules (A. avenaceus). • Spikelet with rachilla prolongation (A. avenaceus)
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’.