The grass genera of the world

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L. Watson and M. J. Dallwitz

Axonopus P. Beauv.

From the Greek axon (axis) and pous (foot), alluding to rachides arising from a common point (digitate).

Including Anastrophus Schlecht., Cabrera Lag., Lappogopsis Steud.

Habit, vegetative morphology. Annual (rarely), or perennial; stoloniferous (sometimes mat-forming), or caespitose. Culms 15–100 cm high (or more?); herbaceous. Culm nodes hairy, or glabrous. Culm internodes solid, or hollow. Leaves mostly basal, or not basally aggregated; non-auriculate. Leaf blades linear-lanceolate to ovate-lanceolate; broad, or narrow; flat, or folded; not pseudopetiolate; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane.

Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence of spicate main branches; digitate (rarely), or non-digitate. Primary inflorescence branches inserted all around the main axis. Rachides hollowed. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund; biseriate. Pedicel apices discoid. Spikelets not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets 1.6–5.4 mm long; oblong, or elliptic, or lanceolate, or ovate, or obovate; adaxial; compressed dorsiventrally; biconvex; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes one per spikelet (membranous); long relative to the adjacent lemmas; dorsiventral to the rachis (the one glume (upper) outside); awnless. Upper glume 4–5 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 0 nerved, or 2 nerved, or 4 nerved (the median lacking); decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas (membranous); not becoming indurated.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes; smooth to striate; becoming indurated to not becoming indurated (papery to crustaceous); yellow in fruit, or brown in fruit; entire; blunt; awnless; hairless; non-carinate; having the margins inrolled against the palea; with a clear germination flap; 4 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; indurated, or not indurated. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary glabrous. Styles free to their bases; free. Stigmas 2; white (e.g. A. rupestris), or red pigmented (usually?).

Fruit, embryo and seedling. Fruit small; ellipsoid; compressed dorsiventrally. Hilum short. Embryo large; waisted; without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally, or markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular, or fusiform (slightly); having markedly sinuous walls. Microhairs present; panicoid-type; 39–45 microns long; 7.5–9 microns wide at the septum. Microhair total length/width at septum 4.3–5.2. Microhair apical cells 21–30 microns long. Microhair apical cell/total length ratio 0.54–0.67. Stomata common; 36–45 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; dumb-bell shaped, or butterfly shaped and dumb-bell shaped.

Transverse section of leaf blade, physiology. C4; biochemical type NADP–ME (1 species); XyMS–. PCR sheath outlines uneven. PCR sheath extensions present, or absent. Maximum number of extension cells 2. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with non-radiate chlorenchyma. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves without flavonoid sulphates (1 species).

Cytology. Chromosome base number, x = 10. 2n = 20, 40, 60, and 80. 2, 4, 6, and 8 ploid.

Taxonomy. Panicoideae; Panicodae; Paniceae. Carpet Grasses.

Distribution, ecology, phytogeography. 114 species; tropical South America. Commonly adventive. Helophytic to mesophytic; species of open habitats; glycophytic. Savanna, forest clearings, moist and weedy places.

Neotropical. Caribbean, Venezuela and Surinam, Amazon, Central Brazilian, Pampas, and Andean. Canadian-Appalachian, Southern Atlantic North American, and Central Grasslands. Sahelo-Sudanian, Somalo-Ethiopian, and South Tropical African.

Rusts and smuts. Rusts — Physopella and Puccinia. Taxonomically wide-ranging species: Puccinia levis. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium and Sphacelotheca.

Economic importance. Significant weed species: A. affinis, A. compressus. Cultivated fodder: A. affinis, A. compressus. Important native pasture species: A. affinis, A. flexuosus. Lawns and/or playing fields: A. compressus.

References, etc. Leaf anatomical: this project.

Illustrations. • A. compressus: Gardner, 1952. • A. affinis: Gibbs Russell et al., 1990. • Inflorescence detail (A. compressus). • Inflorescence detail (A. compressus). • Inflorescence detail (A. compressus). • Spikelet in situ (A. compressus). • Opened spikelet of A. compressus. • Female-fertile lemma of A. affinis. • Caryopsis detail, embryo (A. compressus). Axonopus compressus. ‘Waisted’ embryo. • Abaxial epidermis of leaf blade (A. affinis). • Abaxial epidermis of leaf blade (A. affinis)

The descriptions are offered for casual browsing only. We strongly advise against extracting comparative information from them. This is much more easily achieved using 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, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG).

Cite this publication as: ‘Watson, L., 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: 7th December 2015.’.