The grass genera of the world
Including Achnatherum P. Beauv. p.p., Anatherostipa p.p., Aristella Bertol., Austrostipa S.W.L. Jacobs and J. Everett, Celtica, Hesperostipa (Elias) Barkworth, Jarava Ruiz & Pavon, Lasiagrostis, Macrochloa Kunth, OrthoraphiumNees, Patis Ohwi, Pappostipa, Piptatheropsis p.p., Ptilagrostis Griseb., Sparteum P. Beauv, Stipellula, Timouria Roshev., Trichosantha Steud.
Excluding Anemanthele, Lorenzochloa, Nassella, Orthachne, Trikeraia
Habit, vegetative morphology. Perennial (very rarely annual, e.g. S. capensis); caespitose. Culms 10–250 cm high; woody and persistent (rarely, with persistent canes), or herbaceous; branched above (rarely, but amply so in S. breviglumis, S. elegantissima), or unbranched above (nearly always). The branching simple (nearly always), or suffrutescent, or fastigiate (more or less suffrutescent to fastigiate in S. muelleri). Culm nodes hairy, or glabrous. Culm internodes solid (rarely), or hollow. Young shoots extravaginal (rarely), or intravaginal (nearly always). Leaves mostly basal, or not basally aggregated; auriculate, or non-auriculate. Leaf blades greatly reduced (occasionally), or not all greatly reduced (usually); linear; nearly always narrow; 0.3–5 mm wide; setaceous, or not setaceous; flat (e.g. S. dregeana, S. sibirica), or folded, or rolled, or acicular; without cross venation; persistent; rolled in bud (e.g., Achnatherum), or once-folded in bud. Ligule an unfringed membrane, or a fringed membrane. Contra-ligule present, or absent.
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 to many spikeleted; paniculate; not deciduous; open, or contracted; with capillary branchlets, or without capillary branchlets; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 3–70(–90) mm long (those of sect Stipa especially large); compressed laterally to not noticeably compressed, or not noticeably compressed (more or less terete), or compressed dorsiventrally (sometimes, slightly); disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present (long and sharp-pointed, except in Achnatherum and Ptilagrostis). The callus hairs white, or brown (or orange), or purple. Callus short (Achnatherum, Ptilagrostis), or long; pointed, or blunt (Achnatherum, Ptilagrostis).
Glumes two; very unequal to more or less equal; about equalling the spikelets to exceeding the spikelets; nearly always long relative to the adjacent lemmas; pointed (acute or acuminate); awnless, or awned (sometimes aristate); similar (membranous or papery, acute to acuminate). Lower glume (0–)1–4 nerved (nerveless in Ptilagrostis). Upper glume (0–)3–6 nerved (nerveless or one-nerved in Ptilagrostis). Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas convolute (nearly always, sometimes only basally but often more or less hiding the palea), or not convolute (e.g. Hesperostipa, 2 Austrostipa species); saccate (very rarely - S. gibbosa), or not saccate (nearly always); with an apical crown, or without a crown; decidedly firmer than the glumes (narrow, often hiding the palea); with the abaxial-epidermal silica bodies round to oval (Achnatherum, Austrostipa, Ptilogrostis), square or rectangular (Stipa sensu stricto), or absent (Hesperostipa); becoming indurated (usually, horny), or not becoming indurated (in Achnatherum, Ptilagrostis); entire, or incised (shortly or conspicuously 2-toothed in Achnatherum and Ptilagrostis); when cleft, 2 lobed; when incised, usually not deeply cleft (but deeply cleft in S. gigantea); awned. Awns 1 (mostly), or 3 (sometimes, via aristate lobes, in Achnatherum); median (mostly), or median and lateral; the median different in form from the laterals (when laterals present); from a sinus (Achnatherum, Ptilagrostis), or apical; geniculate (or sometimes bi-geniculate, subulate and non-geniculate in S. saltensis); hairless, or hairy, or long-plumose; much shorter than the body of the lemma to much longer than the body of the lemma (sometimes very long, up to 50 cm in S. pulcherrima); entered by several veins (3); deciduous (infrequently), or persistent (usually, though often with a basal articulation). Lemmas hairy, or hairless (rarely); non-carinate (terete); having the margins inrolled against the palea (when involute - e.g. Hesperostipa, two Austrostipa spp.,), or having the margins lying flat on the palea (mostly, but convolute); without a germination flap; 3–7 nerved. Palea usually present (at least partially enclosed by the lemma); relatively long (usually), or conspicuous but relatively short to very reduced (rarely); convolute around the flower; tightly clasped by the lemma; prow-tipped (Hesperostipa), or not prow-tipped; awnless, without apical setae; thinner than the lemma (usually, translucent), or textured like the lemma (e.g. in Achnatherum, Hesperostipa); indurated (often, more or less, at least the exposed part), or not indurated; seemingly always 2-nerved (numerous former Stipas with nerveless paleas having been transferred to Nassella - Barkworth 1990); keel-less, or 2-keeled. Palea back glabrous, or scabrous, or hairy. Palea keels wingless. Lodicules present; 2 (rarely), or 3 (the posterior commonly smaller). Third lodicule present, or no third lodicule (rarely). Lodicules free; membranous (stipoid); glabrous; not toothed. Stamens 3. Anthers 1.2–9 mm long; penicillate, or not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2, or 3, or 4 (3–4 in Section Barbata); white.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small, or medium sized, or large; fusiform; compressed laterally, or not noticeably compressed. Hilum long-linear. Embryo small; not waisted. Endosperm hard; without lipid; containing only simple starch grains, or containing compound starch grains. Embryo with an epiblast; without a scutellar tail (with a 95–130 degree angle between coleoptile and coleorhiza); with a negligible mesocotyl internode. Embryonic leaf margins meeting.
Seedling with a short mesocotyl, or with a long mesocotyl. First seedling leaf with a well-developed lamina. The lamina narrow; erect; 3–5 veined.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous, or lacking. Papillae present (seemingly rarely), or absent (seen only in some species of Austrostipa); when present, intercostal. Intercostal papillae not over-arching the stomata; several per cell (in a median single or partially double row, circular or branched, at least sometimes of the coronate-pit type, cf. Poa helmsii). Intercostal zones with typical long-cells (nearly always), or with typical long-cells and exhibiting many atypical long-cells (e.g. Austrostipa densiflora). Mid-intercostal long-cells rectangular, or rectangular and fusiform (occasionally with a some distinctly fusiform); having markedly sinuous walls. Microhairs present (probably, sometimes - found to date only adaxially), or absent; elongated; ostensibly one-celled; hard to find and study, seemingly peculiar - thin-walled, perhaps one-celled: see photos in Johnston and Watson 1976. Stomata absent or very rare, or common; (22–)24–45(–48) microns long. Subsidiaries non-papillate; low to high dome-shaped, or triangular. Guard-cells overlapped by the interstomatals, or overlapping to flush with the interstomatals (rarely). Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies tall-and-narrow, or crescentic, or rounded (to elliptical). Costal short-cells conspicuously in long rows, or predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present throughout the costal zones, or confined to the outer files of the costal zones, or present in alternate cell files of the costal zones; horizontally-elongated crenate/sinuous (sometimes, but usually short with only one or two crenations), or horizontally-elongated smooth, or rounded, or saddle shaped, or tall-and-narrow (or cuboid), or crescentic, or panicoid-type (i.e., exhibiting most of the silica body forms, in various combinations from species to species - and often exhibiting many ambiguous, intermediate forms); often cross shaped, or dumb-bell shaped, or nodular; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs, or nodular in section; with the ribs more or less constant in size, or with the ribs very irregular in sizes. Midrib conspicuous, or not readily distinguishable; with one bundle only, or having a conventional arc of bundles (e.g. sometimes in Achnatherum). Bulliforms present in discrete, regular adaxial groups (at the bases of the furrows), or not present in discrete, regular adaxial groups (the bulliform cells small and/or inconspicuous, cf. Ammophila, in many species, but commonly quite large and the groups conspicuous in Austrostipa); when noticeable, in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present, or absent; forming figures, or nowhere forming figures. Sclerenchyma all associated with vascular bundles, or not all bundle-associated. The extra sclerenchyma when present, in abaxial groups, or in a continuous abaxial layer (notably in Stipa sensu stricto, but also in (e.g.) Austrostipa teretifolia).
Phytochemistry. Tissues of the culm bases with abundant starch. Leaves without flavonoid sulphates (3 species).
Cytology. Chromosome base number, x = 9, 10, 11, 12, and 22. 2n = 22, 28, 40, 44, 48, 68, and 96. 2, 4, and 8 ploid (and aneuploids). Nucleoli disappearing before metaphase.
Classification. Watson & Dallwitz (1994): Stipoideae; Stipeae. Soreng et al. (2015): Pooideae; Stipeae. About 300 species.
Distribution, phytogeography, ecology. Tropical and temperate.
Commonly adventive. Mesophytic to xerophytic.
Economic aspects. Significant weed species: the pointed callus of many species (e.g. S. comata, S. spartea) sometimes injuring livestock. Important native pasture species: many important in dry climates, e.g. S. barbata, S. capensis, S. lessingiana. S. tenacissima (Halfa, Esparto grass) used for papermaking mats and cordage.
Hybrids. With Nassella - ×Achnella Barkworth.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia graminella, Puccinia striiformis, and Puccinia monoica. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae Tilletia and Urocystis. Ustilaginaceae Sorosporium, Sphacelotheca, Tolyposporium, and Ustilago.
References, etc. Morphological/taxonomic: de Winter 1965; Barkworth 1983, 1993; Freitag 1985; Vickery Jacobs and Everett 1986; Barkworth and Everett 1987. Leaf anatomical: Metcalfe 1960; studied by us - S. aristiglumis F. Muell. (Austrostipa), S. bigeniculata Hughes (Austrostipa), S. blackii Hubbard (Austrostipa), S. columbiana Maccun (Achnatherum), S. comata Trin. & Rupr. (Hesperostipa), S. densiflora Hughes (Austrostipa), S. elegantissima Labill. (Austrostipa), S. falcata Hughes (Austrostipa), S. falcata scabra (Austrostipa), S. filiculmis Delile (Nassella), S. filifolia Nees (Achnatherum), S. gigantea Link (Achnatherum?), S. ichu Kunth (Jarava), S. leucotricha Trin. & Rupr. (Nassella), S. neomexicana (Thurb.) Scribn. (Ptilagrostis), S. nervosa Vickery (Austrostipa), S. pubescens R. Br. (Austrostipa), S. ramosissima (Trin.) Trin. (Austrostipa), S. teretifolia Steudel. (= stipoides, Austrostipa), S. verticillata Nees & Sprengel (Austrostipa).
Special comments. This sensu lato description is retained, pending preparation of adequately detailed, comparative descriptions for the segregate genera Achnatherum, Austrostipa, Hesperostipa Ptilagrostis and Stipa sensu stricto (see Barkworth and Everett 1987, Barkworth 1993, Jacobs and Everett 1996) and worldwide assignments of species to them. Freitags (1985) preference for sensu lato treatment pending a much needed worldwide monograph has much merit. Illustrations. • S. elegantissima: Gardner, 1952. • S. juncifolia, S. aff. nitida: Gardner, 1952. • S. hemipogon: Gardner, 1952. • S. barbata: P. Beauv. (1812). • Austrostipa mollis, as Stipa: Hutchinson, you hua zhi wu ke zhi shuang zi ye zhi wu (1955). • Austrostipa setacea: Hooker, Fl. Tasmaniae (1860). • Austrostipa stipoides (as Dichelachne): Hooker, Fl. Novae-Zelandiae (1853). • cf. Stipa arundinacea (as Apera): Hooker, Fl. Novae-Zelandiae (1853). • General aspect (S. dregeana): Gibbs Russell et al., 1990. • Ligule of S. (Austrostipa) neesiana. • Leaf-blade auricular hairs in S. (Austrostipa) falcata. Stipa (Austrostipa) falcata. Hairs at the auricular position. • Disarticulated spikelet of S. (Austrostipa) bigeniculata. • Spikelet detail, with base of awn and penicillate stamens. • Spikelet detail. • T.S. of awn showing vascularization in S. spartea: this project. Stipa (Hesperostipa) spartea. Three vascular bundles. • Germination details in S. (Austrostipa) falcata: this project. Stipa (Austrostipa) falcata. Emerging radicle (lower left) and shoot (upper right). Stipa (Austrostipa) falcata. Lemma splitting over the embryo. • Austrostipa bigeniculata, abaxial epidermis of leaf blade: this project. • Austrostipa bigeniculata, abaxial epidermis of leaf blade: this project. • Austrostipa bigeniculata, abaxial epidermis of leaf blade: this project. • Sustrostipa bigeniculata, TS leaf blade: this project. • Austrostipa elegantissima, abaxial epidermis of leaf blade: this project. • Austrostipa densiflora, abaxial epidermis of leaf blade: this project. • TS leaf blade of Austrostipa densiflora: this project. • Austrostipa teretifolia, abaxial epidermis of leaf blade: this project. • Austrostipa blackii, abaxial epidermis of leaf blade: this project. • Austrostipa falcata, abaxial epidermis of leaf blade: this project. • Austrostipa falcata, TS leaf blade: this project. • Austrostipa pubescens, abaxial epidermis of leaf blade: this project. • TS leaf blade of Austrostipa pubescens: this project. • TS leaf blade of Austrostipa pubescens: this project. • Pollen antigens: Watson and Knox (1976)
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’.