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The grass genera of the world

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

Dissanthelium Trin.

From the Greek dissos (double) and anthelion (a small flower), alluding to two florets.

~ Poa

Including Graminiastrum Krause, Phalaridium Nees & Meyen, Stenochloa Nutt

Habit, vegetative morphology. Annual, or perennial (mostly dwarf); rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms herbaceous. Leaves non-auriculate. Leaf blades narrow (with 2 adaxial grooves, cf. Poa); setaceous, or not setaceous; without cross venation. Ligule present; an unfringed membrane; not truncate; 2–6 mm long.

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

Inflorescence. Inflorescence paniculate; open, or contracted; often spicate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 2.5–5 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension naked. Hairy callus absent.

Glumes two; more or less equal; about equalling the spikelets; long relative to the adjacent lemmas (often exceeding all the florets); pointed (acute); awnless; carinate; similar (firm, membranous to herbaceous). Lower glume 1–3 nerved. Upper glume 3 nerved. Spikelets with female-fertile florets only.

Female-fertile florets 2(–3). Lemmas not saccate; less firm than the glumes (membranous); not becoming indurated; entire, or incised; when entire pointed, or blunt; awnless; hairy, or hairless; carinate; without a germination flap; 3–5 nerved. Palea present; conspicuous but relatively short; tightly clasped by the lemma; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; glabrous; toothed; not or scarcely vascularized. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (1.3 mm long); compressed dorsiventrally. Hilum short. Embryo small. Endosperm hard; with lipid; containing compound starch grains. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs absent. Stomata common. Subsidiaries parallel-sided, dome-shaped, and triangular (low to high); including both triangular and parallel-sided forms on the same leaf (and high and low domes). Guard-cells overlapped by the interstomatals (slightly). Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies mostly crescentic, or tall-and-narrow. Costal short-cells predominantly paired. Costal silica bodies rounded, or crescentic (crescents predominating).

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade adaxially flat. Midrib conspicuous (by its ‘hinges’, abaxial keel, and the large vascular bundle possessing only an abaxial strand); with one bundle only. The lamina symmetrical on either side of the midrib (save for the conspicuous ‘midrib hinges’). Bulliforms not present in discrete, regular adaxial groups. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (with the largest bundles, except that of the midrib). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Poeae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Poinae. 17 species.

Distribution, phytogeography, ecology. Mostly Andean, also California Islands, Mexico, Argentina.

Species of open habitats. Mostly in High Andean puna.

References, etc. Leaf anatomical: studied by us - D. minimum Pilger.

Illustrations. • D. californicum: Hook. Ic. Pl. 14 (1880–82). • D. californicum: Hitchcock and Chase (1950)

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: 11th December 2017.’.