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The grass genera of the world

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

Piresiella Judziewicz, Zuloaga & Morone

Name a diminutive from Piresia (a related genus, q.v.).

Habit, vegetative morphology. Delicate perennial (with dimorphic culms); stoloniferous and caespitose. The flowering culms leafless (with 1–2 bladeless sheaths). Culms 3–20 cm high (the flowering culms shorter than the vegetative culms); herbaceous; unbranched above; tuberous; 3–9 noded (the leaves concentrated towards the tips of the vegetative culms). Culm nodes exposed; hairy (retrorsely slightly bearded). Rhizomes pachymorph. Plants unarmed. Leaves not basally aggregated; non-auriculate; without auricular setae. Sheaths glabrous except on one margin, ciliate at the summit. Leaf blades ovate (strongly asymmetrical at the base); broad to narrow; 6–10 mm wide (14–20 mm long); not cordate, not sagittate (the base truncate); flat; shortly pseudopetiolate; persistent; rolled in bud. Ligule an unfringed membrane (ciliolate); truncate; about 0.1 mm long.

Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only and male-only. The male and female-fertile spikelets on different branches of the same inflorescence. The spikelets overtly heteromorphic.

Inflorescence. Inflorescence determinate; of spicate main branches (terminal, exserted, each consisting of two conjugate, ascending, appressed, subequal, unisexual racemes each with 6–9 spikelets, the male raceme somewhat shorter); digitate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’; paired; with very slender rachides. Spikelets solitary; secund (the spikelets on one side of the slender raceme); shortly pedicellate, the male pedicels 0.3–1.5 mm long, the females 0.2–0.6 mm.

Female-sterile spikelets. The male spikelets on slightly shorter racemes, 1.3–1.8 mm long, ellipsoid, glabrous, persistent. Rachilla of male spikelets terminated by a male floret. The male spikelets without glumes; without proximal incomplete florets; 1 floreted. The lemmas awnless. Male florets 1; 2 staminate.

Female-fertile spikelets. Spikelets 4–4.8 mm long; ovoid; compressed dorsiventrally; falling with the glumes (‘or the glumes tardily deciduous’); with a distinctly elongated rachilla internode above the glumes (this 0.3–0.5 mm long, elaiosome-like). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas; hairless; glabrous; pointed (acute to acuminate); awnless; non-carinate; similar (narrowly ovate, chartaceous, sulcate, greenish or whitish, sometimes purple-tipped). Lower glume 3(–5) nerved (with a few cross-veins). Upper glume 3(–5) nerved (with a few cross-veins). Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas similar in texture to the glumes, or decidedly firmer than the glumes (?); becoming indurated, or not becoming indurated (?); more or less mucronate (cucullate or apiculate); hairy (covered with delicate, appressed, white silky hairs); non-carinate; seemingly having the margins inrolled against the palea; ‘not evidently nerved’. Palea present; relatively long (about equalling the lemma); tightly clasped by the lemma; entire; awnless, without apical setae; 2-nerved; 2-keeled. Palea keels wingless. Lodicules present; 3; free. Stamens 0 (no staminodes mentioned). Ovary apically glabrous. Styles free to their bases. Stigmas and styles 3.

Fruit, embryo and seedling. Disseminule a free caryopsis. Fruit free from both lemma and palea; small (2 mm long); ellipsoid; longitudinally grooved; compressed dorsiventrally. Hilum long-linear (as long as the caryopsis). Embryo small (0.2–0.3 mm long).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal (small, circular, confined to the ends of the interstomatals and the stomatal sides of the long-cells adjoining the subsidiaries, and arranged so as to form a beautiful ring around each stomatal apparatus). Intercostal papillae not over-arching the stomata. Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type; (49–)57–69(–75) microns long; 6.3–7.5 microns wide at the septum. Microhair total length/width at septum 9–10.2. Microhair apical cells 24–28.5 microns long. Microhair apical cell/total length ratio 0.4–0.45. Stomata common; (19–)24–27 microns long. Subsidiaries non-papillate; parallel-sided. Guard-cells overlapped by the interstomatals (slightly). Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies oryzoid-type. Macrohairs present near the blade margins. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; ‘panicoid-type’; predominantly short dumb-bell shaped.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with adaxial palisade (one layer); with arm cells (but very obscure in the poor material seen); with fusoids. The fusoids external to the PBS. Leaf blade adaxially flat. Midrib conspicuous (by virtue of its large bundle and relatively massive ‘anchor’ of sclerenchyma); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms in simple fans (between all the bundles). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (most bundles with an ‘anchor’). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Olyreae. Soreng et al. (2015): Bambusoideae; Bambusodae; Olyreae; Olyrinae. 1 species (P. strephioides).

Distribution, phytogeography, ecology. Cuba.

Mesophytic; shade species; glycophytic. Lowland ravines, palm savannas and streambanks.

References, etc. Morphological/taxonomic: Zuloaga et al. (1993). Leaf anatomical: Zuloaga et al. (1993); this project.

Special comments. Segregated from Mniochloa (M. strephioides).


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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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