The grass genera of the world

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L. Watson and M. J. Dallwitz

Apera Adans.

Perhaps from the Greek a (not) and peros (maimed), contrasting the well developed lemma awn with that of Calamagrostis calamagrostis, from which Adanson was distinguishing this genus.

Including Anemagrostis Trin.

Habit, vegetative morphology. Annual; caespitose. Culms 10–120 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes hollow. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; 1–10 mm wide; flat, or rolled (convolute); without cross venation; persistent. Ligule an unfringed membrane; not truncate; 2–10 mm long.

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

Inflorescence. Inflorescence paniculate; open; with capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 2–3.6 mm long; compressed laterally; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret, or terminated by a female-fertile floret; hairless; the rachilla extension when present, with incomplete florets. Hairy callus absent. Callus blunt.

Glumes two; very unequal (usually), or more or less equal (rarely); (the upper) long relative to the adjacent lemmas; pointed; awnless; non-carinate; similar (membranous). Lower glume 1 nerved. Upper glume 3 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets. Spikelets without proximal incomplete florets.

Female-fertile florets 1 (usually), or 2–3. Lemmas bidentate; decidedly firmer than the glumes (firmly membranous); not becoming indurated (‘subindurate when mature’); incised; awned. Awns 1; median; dorsal; from near the top; non-geniculate, or geniculate (rarely); much longer than the body of the lemma; entered by one vein. Lemmas hairless; non-carinate; 5 nerved. Palea present; relatively long; apically notched; awnless, without apical setae; not indurated (hyaline); 2-nerved; 2-keeled, or keel-less. Lodicules present; 2; free; membranous; glabrous; toothed. Stamens 3. Anthers 0.3–2 mm long; not penicillate. Ovary glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; longitudinally grooved; compressed dorsiventrally. Hilum short. Embryo small; not waisted. Endosperm liquid in the mature fruit, or hard; with lipid. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

Seedling with a tight coleoptile. First seedling leaf with a well-developed lamina. The lamina narrow; erect; 3 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (the costals narrower); of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells fusiform; having markedly sinuous walls. Microhairs absent. Stomata common. Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare (very rare); in cork/silica-cell pairs (also solitaries); silicified. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (mainly solitary). Costal silica bodies horizontally-elongated crenate/sinuous, or horizontally-elongated smooth.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size. 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.

Cytology. Chromosome base number, x = 7. 2n = 14. 2 ploid. Chromosomes ‘large’.

Taxonomy. Pooideae; Poodae; Aveneae.

Distribution, ecology, phytogeography. 3–4 species; Europe, western Asia. Commonly adventive. Mesophytic; species of open habitats. Dry sandy soils and arable land.

Holarctic and Antarctic. Boreal and Tethyan. Euro-Siberian. Mediterranean and Irano-Turanian. Patagonian. European and Siberian.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis and Puccinia coronata. Smuts from Tilletiaceae. Tilletiaceae — Tilletia and Urocystis.

Economic importance. Significant weed species: A. interrupta, A. spica-venti.

References, etc. Leaf anatomical: this project.

Illustrations. • A. intermedia: Fl. Iraq, 1968. • A. interrupta (as Agrostis), general aspect: Eng. Bot. (1872). • A. spica-ventae (as Agrostis), general aspect: Eng. Bot. (1872). • Abaxial epidermis of leaf blade (A. spica-ventae)

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.’.