Grass Genera of the World

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; 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. • General aspect. • General aspect. • Inflorescence detail. • Inflorescence detail. • Inflorescence detail. • Spikelet in situ. • Opened spikelet. • Female-fertile lemma. Axonopus affinis. • Caryopsis. Axonopus compressus. ‘Waisted’ embryo. • Abaxial epidermis of leaf blade. Axonopus affinis. • Abaxial epidermis of leaf blade. Axonopus affinis.

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.’ 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).