The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose. Culms 10–60 cm high; herbaceous; tuberous, or not tuberous. Culm nodes glabrous. Culm internodes hollow. Leaves mostly basal; non-auriculate. Leaf blades narrow; flat, or rolled; not pseudopetiolate; without cross venation; persistent; rolled in bud, or once-folded in bud. Ligule a fringe of hairs. Contra-ligule present (of hairs).
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; inbreeding; exposed-cleistogamous, or chasmogamous; with hidden cleistogenes, or without hidden cleistogenes. The hidden cleistogenes (when present) in the leaf sheaths (sometimes basal and very modified).
Inflorescence. Inflorescence few spikeleted; a single raceme, or paniculate; open, or contracted; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets secund, or not secund; pedicellate.
Female-fertile spikelets. Spikelets 6–12(–14) mm long; compressed laterally; disarticulating above the glumes; 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 present.
Glumes two; more or less equal; about equalling the spikelets; long relative to the adjacent lemmas; pointed, or not pointed; awnless; similar (rounded below, keeled above, lanceolate to ovate). Lower glume 3–5 nerved. Upper glume 3–5 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets.
Female-fertile florets 4–6. Lemmas similar in texture to the glumes to decidedly firmer than the glumes; not becoming indurated; incised; not deeply cleft; mucronate (via the central tooth); hairy (short-haired on the lower margins), or hairless. The hairs not in tufts; not in transverse rows. Lemmas non-carinate; 7–9 nerved. Palea present; relatively long; entire; awnless, without apical setae; 2-nerved; 2-keeled. Palea keels wingless (but each enlarging and progressively thickening towards the base - by contrast with Danthonia sensu stricto?). Lodicules present; fleshy; glabrous. Stamens 3. Anthers 0.2–0.4 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small; longitudinally grooved. Hilum long-linear. Embryo large (compared with Danthonia sensu stricto); waisted. Endosperm hard; without lipid. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
Seedling with a long mesocotyl; with a loose coleoptile. First seedling leaf with a well-developed lamina. The lamina narrow; 5 veined.
Ovule, embryology. Outer integument covering no more than the chalazal half of the ovule. Inner integument discontinuous distally. Synergids haustorial.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower); of similar wall thickness costally and intercostally (rather thick walled, and heavily pitted anticlinally and on the surface). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type (large); (78–)81–99(–102) microns long; (12–)12.6–15(–18) microns wide at the septum. Microhair total length/width at septum 4.3–7.9. Microhair apical cells (36–)40.5–46.5(–52.5) microns long. Microhair apical cell/total length ratio 0.44–0.52. Stomata absent or very rare (scarce in material seen), or common (see Metcalfe); 31–34 microns long. Subsidiaries dome-shaped and triangular (of the truncated type, in the material seen). Guard-cells overlapped by the interstomatals (very slightly), or overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (and solitary); silicified. Intercostal silica bodies mostly tall-and-narrow, or crescentic (a few cubical or saddle-shaped). Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; short dumb-bell shaped, or cross shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade; without circular cells (but often with a region of translucent, spongy tissue in the mid-interveinal regions of the mesophyll). Leaf blade with distinct, prominent adaxial ribs to adaxially flat (the adaxial ribs very slight); with the ribs more or less constant in size. Midrib conspicuous (by virtue of the large associated hinge groups); with one bundle only. Bulliforms present in discrete, regular adaxial groups (these conspicuous, in all the slight furrows); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (the midrib with an anchor, the rest of the bundles with Is). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 6, or 9 (?). 2n = 24, 36, and 124. 3, 4, and 14 ploid. Chromosomes fairly small.
Classification. Watson & Dallwitz (1994): Arundinoideae; Danthonieae. Soreng et al. (2015): Danthonioideae; Danthonieae. 1 species.
Distribution, phytogeography, ecology. Madeira, Algeria, Europe, Asia Minor.
Hybrids. Intergeneric hybrids with Danthonia (×Danthosieglingia Domin).
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia brachypodii.
References, etc. Leaf anatomical: Metcalfe 1960; this project.
Illustrations. • S. decumbens (as Triodia), general aspect: Eng. Bot. (1872). • General aspect (S. decumbens): John Curtis, 1824. • S. decumbens, 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: 13th November 2017. delta-intkey.com/grass’.