Aristida L.
From the Latin arista or the Greek aristos (bristle, or awn from an ‘ear’ of corn).
Including Aristopsis Catasus, Arthratherum P. Beauv., Chaetaria P. Beauv., Curtopogon P. Beauv., Kielboul Adans., Moulinsia Raf., Streptachne R. Br., Trixostis Raf.
Habit, vegetative morphology. Annual, or perennial; caespitose. Culms 10–100(–180) cm high; herbaceous; branched above, or unbranched above. Culm nodes glabrous. Culm internodes solid, or hollow. Leaves mostly basal, or not basally aggregated (in annual species); non-auriculate. Leaf blades linear, or linear-lanceolate; narrow; flat, or rolled; not pseudopetiolate; without cross venation; persistent; rolled in bud, or once-folded in bud; ligule present; a fringed membrane to a fringe of hairs. Contra-ligule present (of hairs), or absent.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality. Plants exposed-cleistogamous, or chasmogamous; with hidden cleistogenes, or without hidden cleistogenes. The hidden cleistogenes in the leaf sheaths (when present).
Inflorescence. Inflorescence few spikeleted, or many spikeleted; paniculate; deciduous in its entirety, or not deciduous; open, or contracted. Rachides hollowed, or flattened, or winged, or neither flattened nor hollowed, not winged. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 4–30 mm long; compressed laterally to not noticeably compressed; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus long; pointed.
Glumes two; relatively large; very unequal to more or less equal; (at least the G2) about equalling the spikelets, or exceeding the spikelets; usually pointed; awned, or awnless; carinate; very dissimilar, or similar (membranous to papery). Lower glume 1 nerved. Upper glume 1 nerved (usually), or 3 nerved (rarely). Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas narrow, cylindrical; convolute, or not convolute; decidedly firmer than the glumes; becoming indurated to not becoming indurated (leathery to indurated); entire; awned. Awns triple or trifid, commonly with a basal column (usually), or not of the triple/trifid, basal column type (the column sometimes absent, the lateral branches sometimes reduced or absent); 1, or 3; apical; non-geniculate (at least, not geniculate in the normal sense); hairless (usually glabrous); much shorter than the body of the lemma to much longer than the body of the lemma; entered by several veins (usually with three veins in the column); deciduous, or persistent. Lemmas hairy (rarely), or hairless; glabrous, or scabrous; non-carinate; with a clear germination flap; 1–3 nerved. Palea present; conspicuous but relatively short, or very reduced (enclosed by the lemma); entire; awnless, without apical setae; thinner than the lemma (hyaline); not indurated; 1-nerved, or 2-nerved, or nerveless. Lodicules present, or absent; when present, 2; free; membranous; ciliate (rarely), or glabrous; not toothed; rather heavily vascularized. Stamens 1–3. Anthers 0.7–2 mm long; not penicillate. Ovary glabrous. Styles free to their bases. Stigmas 2; red pigmented, or brown.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small to large (3–11 mm long); fusiform; compressed dorsiventrally, or not noticeably compressed. Hilum short, or long-linear. Embryo large; waisted, or not waisted. Endosperm hard; without lipid; containing compound starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode; with one scutellum bundle. Embryonic leaf margins meeting.
Seedling with a short mesocotyl. First seedling leaf with a well-developed lamina. The lamina narrow; curved; 3–5 veined.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (or somewhat obscure in some species). Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (usually fairly thick walled). Mid-intercostal long-cells rectangular (and narrow); having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type; 48–81(–87) microns long; 5–9.6 microns wide at the septum. Microhair total length/width at septum 8.4–12. Microhair apical cells 24–44 microns long. Microhair apical cell/total length ratio 0.4–0.6. Stomata common; 22.5–36 microns long. Subsidiaries dome-shaped, or triangular, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; in cork/silica-cell pairs (and solitaries); silicified (when paired), or not silicified (when solitary). Intercostal silica bodies variable in shape. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous, or horizontally-elongated smooth, or rounded, or saddle shaped, or tall-and-narrow, or crescentic, or oryzoid, or ‘panicoid-type’; when panicoid type, variously cross shaped to dumb-bell shaped, or nodular (often exhibiting elongated dumb-bells with enlarged, bulbous ends, and/or very large, nodular forms).
Transverse section of leaf blade, physiology. C4. The anatomical organization unconventional. Organization of PCR tissue Aristida type. Biochemical type NADP–ME (3 species); XyMS– (with double PCR sheaths). PCR cells without a suberised lamella. PCR cell chloroplasts ovoid; with well developed grana (in the outer sheath), or with reduced grana (in the inner sheath); centrifugal/peripheral (in the inner sheath), or centripetal (in the outer sheath). Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (usually), or not traversed by colourless columns (e.g. in A. caput-medusae). Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes. Midrib conspicuous, or not readily distinguishable; with one bundle only. Bulliforms associated with colourless mesophyll cells to form deeply-penetrating fans (these often linked with colourless girders, the latter fully traversing or not). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles, or not all bundle-associated. The ‘extra’ sclerenchyma when present, in abaxial groups; abaxial-hypodermal, the groups continuous with colourless columns.
Culm anatomy. Culm internode bundles in three or more rings, or scattered.
Phytochemistry. Leaves without flavonoid sulphates (6 species). Leaf blade chlorophyll a:b ratio 4.46–4.65.
Cytology. Chromosome base number, x = 11 and 12. 2n = 22, 24, 36, 44, 48, and 66. 2, 4, and 6 ploid. Chromosomes ‘small’. Nucleoli persistent.
Taxonomy. Arundinoideae; Aristideae. Threeawn grasses, Kerosene grasses.
Distribution, ecology, phytogeography. 290 species; temperate and subtropical. Xerophytic.
Holarctic, Paleotropical, Neotropical, Cape, Australian, and Antarctic. Boreal, Tethyan, and Madrean. African, Madagascan, Indomalesian, Polynesian, and Neocaledonian. Euro-Siberian, Atlantic North American, and Rocky Mountains. Macaronesian, Mediterranean, and Irano-Turanian. Saharo-Sindian, Sudano-Angolan, West African Rainforest, Namib-Karoo, and Ascension and St. Helena. Indian, Indo-Chinese, Malesian, and Papuan. Fijian. Caribbean, Venezuela and Surinam, Amazon, Central Brazilian, Pampas, and Andean. North and East Australian and Central Australian. Patagonian. European and Siberian. Canadian-Appalachian, Southern Atlantic North American, and Central Grasslands. Sahelo-Sudanian, Somalo-Ethiopian, South Tropical African, and Kalaharian. Tropical North and East Australian and Temperate and South-Eastern Australian.
Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis and Puccinia aristidae. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Tilletia. Ustilaginaceae — Sorosporium, Sphacelotheca, Tolyposporium, and Ustilago.
Economic importance. Significant weed species: (e.g.) A. adscensionis, A. dichotoma, A. longiseta, A. oligantha - the awns of many species can injure livestock. Important native pasture species: none - generally poor value, but various species of minor grazing value in dry regions.
References, etc. Morphological/taxonomic: de Winter 1965; Lazarides 1980. Leaf anatomical: mainly from Metcalfe 1960 and this project.
Illustrations. • General aspect. • General aspect. • Inflorescence. • Spikelet. Aristida ramosa. • Spikelets. • Spikelets. • Lemmas. • Abaxial epidermis of leaf blade. Aristida ramosa. • Abaxial epidermis of leaf blade. • Transverse section of leaf blade. Aristida biglandulosa. • Transverse section of leaf blade. Aristida biglandulosa. Fluorescence image. • Transverse section of leaf blade. Aristida biglandulosa. Autofluorescence image. • Transverse section of leaf blade. Aristida behriana. Autofluorescence image. • Transverse section of leaf blade. • Germination. Aristida ramosa. Radicle emerging between raised flap and callus, shoot emerging between the overlapping lemma margins (lower left). • Germination. Aristida ramosa. Radicle emerging between raised germination flap and callus, shoot (upper left) from between the rolled lemma margins.
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
