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The grass genera of the world

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

Poidium Nees

~ Poa, Chascolytrum

Habit, vegetative morphology. Perennial; caespitose. Culms 50–150 cm high (?); herbaceous; unbranched above. Young shoots intravaginal. Leaves non-auriculate. The fibrous remains of the sheaths persisting. Leaf blades narrow; flat, or folded; without cross venation; persistent. Ligule an unfringed membrane.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; exposed-cleistogamous, or chasmogamous.

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

Female-fertile spikelets. Spikelets compressed laterally; disarticulating above the glumes; disarticulating between the florets; with a distinctly elongated rachilla internode above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two; more or less equal; about equalling the spikelets; long relative to the adjacent lemmas; hairless; glabrous; awnless; carinate; similar (linear lanceolate or narrowly lanceolate). Lower glume 1 nerved, or 3 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1; merely underdeveloped (rudimentary).

Female-fertile florets 2–4. Lemmas lanceolate; not becoming indurated; entire; awnless; hairless; scabrous; carinate; without a germination flap; 5 nerved. Palea present; relatively long (narrow); awnless, without apical setae; not indurated; 2-nerved; 2-keeled (sulcate between the keels). Lodicules present; 2; free; membranous; glabrous; not toothed (acute). Stamens 1. Ovary apically glabrous. Stigmas 2.

Fruit, embryo and seedling. Fruit longitudinally grooved (ventrally sulcate); not noticeably compressed to trigonous (subtrigonous); hairy on the body. Hilum short.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls (these conspicuously pitted). Microhairs absent. Stomata absent or very rare (in places), or common (in places, but then confined to single files adjacent to the costae). Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals (but only very slightly so). Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies crescentic. Large, round prickle bases fairly common. Crown cells absent. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (mostly in pairs and short rows). Costal silica bodies horizontally-elongated crenate/sinuous (short versions of the crenate type predominating), or ‘panicoid-type’ (if a few deeply crenate forms are so interpreted); if classifiable as panicoid type, nodular; not sharp-pointed.

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 more or less constant in size (flat- to round-topped). Midrib not readily distinguishable; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (in all the furrows); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (most bundles with a large T - the adaxial girders generally being the more massive). Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. Lemmas not as in Briza (q.v.). Female-fertile lemma not as in Lombardochloa (q.v.).

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Poeae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Calothecinae. 2 species.

Distribution, phytogeography, ecology. Tropical Brazil.

References, etc. Morphological/taxonomic: Nicora and Rúgolo de Agrasar 1981. Leaf anatomical: this project.


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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’.

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