The grass genera of the world
~ Trisetum, Trisetaria
Type species: Type: A. michelii (Savi) Parl.
Habit, vegetative morphology. Annual; caespitose. Culms 2–30 cm high; herbaceous. Culm nodes glabrous. Culm internodes hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear; apically cucullate; narrow; flat, or rolled (involute); without cross venation; persistent. Ligule an unfringed membrane to a fringed membrane (short, often hairy outside); truncate; 0.4–1 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open, or contracted; when contracted spicate, or more or less irregular. Primary inflorescence branches borne distichously. Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 3–5 mm long; compressed laterally; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret; hairy.
Glumes two; very unequal; (the longer) long relative to the adjacent lemmas; pointed; awnless; carinate; similar. 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.
Female-fertile florets 2–4. Lemmas often apically split; similar in texture to the glumes; not becoming indurated; entire (but often splitting); not deeply cleft; awned. Awns 1; median; dorsal; from near the top (though often described as from the sinus); non-geniculate; much shorter than the body of the lemma; entered by one vein. Lemmas hairless; non-carinate; 3 nerved. Palea present; conspicuous but relatively short; deeply bifid; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; glabrous; not toothed. Stamens 3. Anthers 0.5 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small. Hilum short. Embryo small. Endosperm liquid in the mature fruit; with lipid.
Abaxial leaf blade epidermis. Papillae absent. Mid-intercostal long-cells 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. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous to horizontally-elongated smooth, or saddle shaped, or panicoid-type (sometimes); sometimes indisputably nodular.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms inconspicuous in the poor material seen. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 7. 2n = 12.
Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Aveninae. 2 species.
Distribution, phytogeography, ecology. Mediterranean.
Not commonly adventive. Mesophytic, or xerophytic.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia hordei. Smuts from Tilletiaceae. Tilletiaceae Tilletia.
References, etc. Leaf anatomical: this project.
Illustrations. • A. michelii: Gardner, 1952. • A. michelii, abaxial epidermis of leaf blade: this project
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: 13th November 2017. delta-intkey.com/grass’.