| # The grass genera of the world |

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

### Airopsis Desv.

Including Aeropsis Aschers. & Graebn., Sphaerella Bub.

Habit, vegetative morphology. Very slender annual. Culms 3–25 cm high; herbaceous. Leaves non-auriculate. The uppermost sheath somewhat inflated. Leaf blades linear; narrow; to 1.5 mm wide; setaceous; rolled (convolute); without cross venation. Ligule an unfringed membrane; not truncate; 1–2 mm long.

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

Inflorescence. Inflorescence paniculate; 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 (the pedicels clavate).

Female-fertile spikelets. Spikelets 1.2–1.5 mm long; subspherical; not noticeably compressed; disarticulating above the glumes; with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; relatively large; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas; conspicuously ventricose; hairless (smooth, shining); pointed; awnless; non-carinate; similar. Lower glume 3 nerved (the laterals faint). Upper glume 3 nerved (the laterals faint). Spikelets with female-fertile florets only.

Female-fertile florets 2. Lemmas 3-dentate; similar in texture to the glumes; not becoming indurated; incised; not deeply cleft; awnless; hairy (puberulent); non-carinate; without a germination flap; 3 nerved. Palea present; relatively long; tightly clasped by the lemma; entire to apically notched (truncate to slightly denticulate); awnless, without apical setae; not indurated; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; glabrous; not toothed; not or scarcely vascularized. Stamens 3. Anthers 0.3 mm long. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (0.5–0.6 mm long); subglobose (‘hemispherical’); compressed dorsiventrally. Hilum short (punctate). Embryo small. Endosperm liquid in the mature fruit.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells fusiform; having straight or only gently undulating walls. Microhairs absent. Stomata common. Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. Prickles common. Crown cells absent. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies absent to poorly developed; imperfectly horizontally-elongated crenate/sinuous.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes. Midrib not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (seemingly, in the poor material seen). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (all the main bundles with adaxial strands and abaxial girders).

Cytology. Chromosome base number, x = 4. 2n = 8. 2 ploid.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Brizinae. 1 species (A. tenella).

Distribution, phytogeography, ecology. Northwest Africa and southwest Europe to Sicily.

Mesophytic to xerophytic; species of open habitats. Sandy places.

References, etc. Leaf anatomical: studied by us.

Illustrations. • Airopsis tenella: Coste, Fl. de France (1906).

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: 15th June 2025. delta-intkey.com’.

Contents