Perotis Aiton
From the Greek petros (deficient), ous, otis (ear), referring to the minute palea.
Including Xystidium Trin.
Habit, vegetative morphology. Annual, or perennial (rarely); caespitose. Culms 12–100 cm high; herbaceous. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades narrow (but relatively broad at the base); cordate, or not cordate, not sagittate; flat or folded; without abaxial multicellular glands; without cross venation; persistent; an unfringed membrane to a fringed membrane.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence a single spike, or a single raceme (a narrow ‘bottlebrush’, bearded by the long glume awns); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary (often reflexing when mature); not secund; subsessile to pedicellate.
Female-fertile spikelets. Spikelets 1.2–5.5 mm long; compressed laterally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present, or absent.
Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas (considerably exceeding them); hairy (often), or hairless; awned; carinate; similar (narrow, membranous to cartilaginous, tipped by long capillary awns). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas lanceolate; less firm than the glumes (hyaline); not becoming indurated; entire; pointed, or blunt; awnless; hairless; glabrous; carinate; 1 nerved. Palea present; conspicuous but relatively short (but almost equalling the lemma); not indurated (hyaline); nerveless. Lodicules present; 2; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary glabrous. Styles fused. Stigmas 2.
Fruit, embryo and seedling. Fruit small to medium sized (almost as long as the glumes); longitudinally grooved; compressed dorsiventrally, or not noticeably compressed. Hilum short. Pericarp fused. Embryo large. Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 10–18 microns long. Microhair basal cells 7–8 microns long. Microhairs (5.4–)6–8.5(–9) microns wide at the septum. Microhair total length/width at septum 2–3.3. Microhair apical cells 4–9 microns long. Microhair apical cell/total length ratio 0.38–0.6. Stomata common; 21–27 microns long. Subsidiaries low to high dome-shaped and triangular. Intercostal short-cells absent or very rare. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; cross shaped, or dumb-bell shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells. Leaf blade adaxially flat. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans (often linked with traversing colourless girders). Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Culm anatomy. Culm internode bundles in one or two rings, or in three or more rings.
Cytology. Chromosome base number, x = 10. 2n = 36, or 40.
Taxonomy. Chloridoideae; main chloridoid assemblage.
Distribution, ecology, phytogeography. 10 species; Africa, India, Ceylon, eastern Asia, Australia. Mesophytic, or xerophytic; species of open habitats; glycophytic. Savanna and grassland, often ruderal.
Paleotropical and Australian. African, Madagascan, and Indomalesian. Saharo-Sindian, Sudano-Angolan, West African Rainforest, and Namib-Karoo. Indian, Indo-Chinese, Malesian, and Papuan. North and East Australian. Sahelo-Sudanian, Somalo-Ethiopian, South Tropical African, and Kalaharian. Tropical North and East Australian.
Rusts and smuts. Rusts — Puccinia. Smuts from Tilletiaceae. Tilletiaceae — Tilletia.
References, etc. Leaf anatomical: Metcalfe 1960; this project.
Illustrations. • General aspect, spikelets. • General aspect. • Abaxial epidermis of leaf blade. • Transverse section 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).
