The grass genera of the world
Habit, vegetative morphology. Robust perennial; rhizomatous. Culms 60–350 cm high; herbaceous. Culm internodes solid. Leaves non-auriculate. Leaf blades harsh; narrow; flat, or rolled; not pseudopetiolate; without cross venation. Ligule a fringed membrane; not truncate; 6–12 mm long.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 10–15 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairy (villous). Hairy callus present.
Glumes two; more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; pointed (acuminate); awnless; carinate; similar (firmly membranous). Lower glume 3–5 nerved. Upper glume 3–5 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 2–6 (?). Lemmas decidedly firmer than the glumes (leathery); not becoming indurated; incised; 2 lobed; not deeply cleft (shortly bidentate); mucronate, or awned. Awns when present, 1; from a sinus, or apical; non-geniculate; much shorter than the body of the lemma. Lemmas hairy (on the lower half); carinate to non-carinate; 5–7 nerved. Palea present; relatively long; apically notched (bidentate); awnless, without apical setae; 2-nerved; 2-keeled. Lodicules present; 3; free; membranous; ciliate (on the margins); not toothed; not or scarcely vascularized. Stamens 3. Anthers not penicillate. Ovary hairy. Styles free to their bases. Stigmas 2; white.
Fruit, embryo and seedling. Fruit medium sized (about 7 mm long); with hairs confined to a terminal tuft. Hilum long-linear. Embryo small. Endosperm hard. 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 (l/b ratio 70); curved; 7 veined.
Abaxial leaf blade epidermis. Costal/intercostal zonation lacking. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs absent. Stomata absent or very rare; 28.5–30 microns long. Intercostal short-cells common; in cork/silica-cell pairs. Intercostal silica bodies elliptic. Costal short-cells predominantly paired. Costal silica bodies rounded (mostly, elliptical), or tall-and-narrow.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs (flat-topped ribs); with the ribs very irregular in sizes. Midrib not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups; in the furrows, in ill-defined groups of irregularly sized cells cf. Ammophila. All the vascular bundles accompanied by sclerenchyma. Sclerenchyma not all bundle-associated. The extra sclerenchyma in a continuous abaxial layer.
Cytology. Chromosome base number, x = 12 (chromosomes small). 2n = 48 and 96. 4 and 8 ploid.
Taxonomy. Stipoideae; Ampelodesmeae.
Distribution, ecology, phytogeography. 1 species; Mediterranean. Xerophytic (mainly coastal).
Holarctic. Boreal and Tethyan. Euro-Siberian. Mediterranean. European.
Economic importance. A component of Esparto grass, used for papermaking.
References, etc. Morphological/taxonomic: Decker 1964b; Macfarlane and Watson 1980. Leaf anatomical: Metcalfe 1960; this project.
Special comments. An isolated monotypic genus, of uncertain taxonomic affinities in spite of the good descriptive data. A prime candidate for comparative DNA studies.
Illustrations. • Abaxial epidermis of leaf blade (A. mauritanicus). • Transverse section of leaf blade (A. mauritanicus)
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: 2nd April 2015. delta-intkey.com’.