Astrebla F. Muell.
From the Greek a (not) and streblos (twisted), in reference to the straight awns.
Habit, vegetative morphology. Perennial; caespitose. Culms 30–90(–120) cm high; herbaceous; branched above. Culm nodes glabrous. Culm internodes solid. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; (3–)4–6(–8) mm wide; without abaxial multicellular glands; without cross venation; persistent; rolled in bud; a fringe of hairs.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets; exposed-cleistogamous, or chasmogamous.
Inflorescence. Inflorescence a single spike, or of spicate main branches, or a single raceme (with short pedicels); digitate, or non-digitate (when the racemes solitary). Primary inflorescence branches 1, or 2. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund; biseriate; sessile to subsessile, or pedicellate (with short pedicels); imbricate (cuneate).
Female-fertile spikelets. Spikelets 7–18 mm long (including the lobes); compressed laterally; disarticulating above the glumes; not disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus absent.
Glumes two; very unequal to more or less equal; shorter than the spikelets, or about equalling the spikelets; shorter than the adjacent lemmas, or long relative to the adjacent lemmas; pointed (acute); awnless; carinate; similar (membranous to papery). Lower glume 1–9 nerved. Upper glume 7–16 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. Spikelets without proximal incomplete florets.
Female-fertile florets 1–4. Lemmas decidedly firmer than the glumes (leathery); not becoming indurated; incised; 3 lobed; deeply cleft; awned. Awns 1 (by terminal extension of the median lobe), or 3 (by extensions of all three lobes); median, or median and lateral; the median similar in form to the laterals (when laterals present); from a sinus, or apical; non-geniculate; often curved; hairless; much shorter than the body of the lemma to much longer than the body of the lemma. The lateral awns when present, shorter than the median to about equalling the median. Lemmas basally hairy; non-carinate (dorsally rounded); 3–11 nerved. Palea present; entire (acuminate); awnless, without apical setae; not indurated (firmly membranous to papery); 2-nerved; 2-keeled. Palea keels wingless (ciliate). Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small; ellipsoid; longitudinally grooved; compressed dorsiventrally, or not noticeably compressed. Hilum short. Pericarp free. Embryo large. Endosperm containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae not over-arching the stomata; consisting of one symmetrical projection per cell (at least in A. pectinata). Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (quite thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical, or elongated; chloridoid-type (basal cells short). Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 22–26 microns long. Microhair basal cells 12 microns long. Microhairs 12–13.5 microns wide at the septum. Microhair total length/width at septum 1.7–2. Microhair apical cells 9.6–15 microns long. Microhair apical cell/total length ratio 0.43–0.54. Stomata common; 21–24 microns long. Subsidiaries non-papillate; dome-shaped (mainly, in A. pectinata), or triangular, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired; silicified and not silicified. Intercostal silica bodies imperfectly developed; narrowly saddle shaped. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; large, saddle shaped.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; biochemical type NAD–ME (4 species); XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles complete to interrupted (only midrib); interrupted both abaxially and adaxially. PCR sheath extensions present, or absent. Maximum number of extension cells when present, 1–7. PCR cells without a suberised lamella. PCR cell chloroplasts elongated; with well developed grana; centripetal. Mesophyll with radiate chlorenchyma; not Isachne-type (but with very narrow-elongate PCA cells in A. pectinata); traversed by columns of colourless mesophyll cells. Leaf blade ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially, or without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups (the groups large); associated with colourless mesophyll cells to form deeply-penetrating fans (these linking with the colourless columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’, or nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Phytochemistry. Leaf blade chlorophyll a:b ratio 4.17–4.53.
Cytology. Chromosome base number, x = 10. 2n = 40.
Taxonomy. Chloridoideae; main chloridoid assemblage. Mitchell Grasses.
Distribution, ecology, phytogeography. 4 species; Australia. Xerophytic; species of open habitats. Dry clay grassland.
Australian. North and East Australian and Central Australian. Tropical North and East Australian.
Rusts and smuts. Rusts — Puccinia.
Economic importance. Cultivated fodder: A. lappacea. Important native pasture species: all species palatable and valuable.
References, etc. Leaf anatomical: Metcalfe 1960 and this project.
Illustrations. • General aspect. • Inflorescence. • Spikelets. • Spikelet. • Floret. • Floret. • Abaxial epidermis of leaf blade. • Transverse section of leaf blade. • Transverse section of leaf blade
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).
