Mesosetum Steud.
Including Bifaria (Hack.) Kuntze, Peniculus Swallen
Habit, vegetative morphology. Annual, or perennial; stoloniferous, or caespitose. Culms herbaceous. Culm nodes hairy. Culm internodes hollow. Leaves mostly basal, or not basally aggregated; non-auriculate. Leaf blades narrow; flat, or rolled (convolute); not pseudopetiolate; without cross venation; persistent; a fringed membrane, or a fringe of hairs.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence a single spike, or a single raceme (with subsessile spikelets). Rachides hollowed to flattened, or winged (membranously, in M. ansatum). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; not secund; biseriate; subsessile.
Female-fertile spikelets. Spikelets adaxial; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present, or absent.
Glumes two; very unequal; (the upper) long relative to the adjacent lemmas; dorsiventral to the rachis; hairy (the upper only, or both), or hairless; (the lower) awned (or mucronate, sometimes), or awnless; carinate (the upper strongly keeled, slightly winged). Lower glume 3 nerved. Upper glume (3–)5(–7) nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate, or epaleate. Palea of the proximal incomplete florets when present, reduced (hyaline). The proximal incomplete florets sterile. The proximal lemmas usually hyaline down the middle; awnless; 5 nerved; decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas; not becoming indurated.
Female-fertile florets 1. Lemmas similar in texture to the glumes to decidedly firmer than the glumes (leathery); smooth; not becoming indurated; entire; acute to mucronate; awnless; hairless; glabrous; non-carinate; having the margins lying flat on the palea; with a clear germination flap; 5 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma (apart from the hyaline margins); 2-nerved; keel-less. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers not penicillate. Ovary glabrous. Styles free to their bases. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small; longitudinally grooved; compressed laterally (slightly), or not noticeably compressed. Hilum long-linear (at least in M. pittieri). Embryo large to small; not waisted. Endosperm hard.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells having markedly sinuous walls. Microhairs present; ostensibly one-celled (the apical cells bulbous-based with pointed tips, seemingly lying horizontally over short, embedded basal cells); small, peculiar and hard to interpret in both species seen - cf. Coelachne, Coelachyrum?. Stomata common; 43.5–54 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Costal short-cells conspicuously in long rows (M. loliiforme), or neither distinctly grouped into long rows nor predominantly paired (M. pittieri). Costal silica bodies ‘panicoid-type’; mostly cross shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS– (but variable in bundles of M. loliiforme). Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size. Midrib not readily distinguishable (slightly larger); having a conventional arc of bundles (1 large, 2 small). Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (M. loliforme), or absent (M. pittieri); nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles (excluding the blade margins).
Cytology. 2n = 16.
Taxonomy. Panicoideae; Panicodae; Paniceae.
Distribution, ecology, phytogeography. 35 species; Central & tropical South America, West Indies. Species of open habitats. Savanna.
Neotropical. Caribbean, Venezuela and Surinam, Central Brazilian, and Andean.
Rusts and smuts. Smuts from Ustilaginaceae. Ustilaginaceae — Sphacelotheca.
References, etc. Leaf anatomical: this project.
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).