Piresia Swallen
Named for J.M. Pires, Brazilian botanist.
Habit, vegetative morphology. Perennial. The flowering culms mostly leafless (and decumbent in the leaf litter, but erect foliage culms also sometimes having a terminal inflorescence). Culms 8–40 cm high; herbaceous; unbranched above. Plants unarmed. Leaves not basally aggregated; without auricular setae. Leaf blades pseudopetiolate; cross veined. Contra-ligule absent.
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 mixed in the inflorescence (one or two males beneath each female). The spikelets overtly heteromorphic.
Inflorescence. Inflorescence paniculate (depauperate, racemelike); spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs (with spatheoles?). Spikelet-bearing axes ‘racemes’, or paniculate; persistent. Spikelets in triplets, or paired; not secund; not in distinct ‘long-and-short’ combinations.
Female-sterile spikelets. Male spikelets usually lacking glumes, with 3 free, non-penicillate stamens. Rachilla of male spikelets terminated by a male floret. The male spikelets usually without glumes; without proximal incomplete florets. Male florets 1; 3 staminate. The staminal filaments free.
Female-fertile spikelets. Spikelets 5–7 mm long; narrowly elliptic; with conventional internode spacings. Rachilla terminated by a female-fertile floret.
Glumes two; more or less equal; long relative to the adjacent lemmas; pointed; awnless (apiculate); non-carinate; similar (herbaceous). Lower glume 3 nerved, or 5 nerved. Upper glume 3 nerved, or 5 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas decidedly firmer than the glumes (leathery); becoming indurated; awnless; hairy (appressed pilose); non-carinate; having the margins inrolled against the palea. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; indurated; 2-nerved. Stamens 0 (staminodes 0 or three). Styles fused. Stigmas 2.
Fruit, embryo and seedling. Fruit compressed dorsiventrally. Hilum long-linear. Embryo small.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present (and very abundant); costal and intercostal (but far more conspicuous intercostally). Intercostal papillae over-arching the stomata; several per cell (one or two irregular rows of irregularly shaped, rather angular papillae per long-cell). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type; 24–39 microns long; 3.6–4.5 microns wide at the septum. Microhair total length/width at septum 7.7–10.8. Microhair apical cells 15–17.5 microns long. Microhair apical cell/total length ratio 0.4–0.45. Stomata common; 18–21 microns long. Subsidiaries papillate (commonly two on each); high dome-shaped (mostly), or triangular. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies vertically elongated-nodular. Large, cushion-based macrohairs common. Crown cells absent. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; mostly Maltese- cross shaped (sometimes almost ‘oryziod’), or butterfly shaped to dumb-bell shaped (a few, short); not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with adaxial palisade; with arm cells (the cells adjoining the fusoids with a few large and conspicuous ingrowths); with fusoids. The fusoids external to the PBS. Leaf blade adaxially flat. Midrib conspicuous (by virtue of its large bundle and adaxially prominent rib); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; in simple fans (the groups large and wide, one in each intercostal zone). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (all the bundles with a small ‘anchor’, except the midrib with strands only). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 11. 2n = 22. 2 ploid.
Taxonomy. Bambusoideae; Oryzodae; Olyreae.
Distribution, ecology, phytogeography. 4 species; tropical America. Mesophytic; shade species.
Neotropical. Caribbean, Venezuela and Surinam, Amazon, and Central Brazilian.
References, etc. Morphological/taxonomic: Swallen 1964; Soderstrom 1982b. Leaf anatomical: this project.
Illustrations. • Abaxial epidermis of leaf blade. • Abaxial epidermis of leaf blade
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
