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The grass genera of the world

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

Leersia Soland.

Named for J.D.Leers, eighteenth century German physician and botanist.

Type species: Type: not designated; lecto: L. oryzoides (L.) Sw. (typ. cons.).

Including Aplexia Faf., Asprella Schreb., Blepharochloa Endl., Ehrhartia Weber, Endodia Raf., Homalocenchrus Mieg, Laertia Gromov, Pseudoryza Griff., Turraya Wall.

Habit, vegetative morphology. Annual (rarely), or perennial; rhizomatous, or stoloniferous, or caespitose. Culms 30–150 cm high; herbaceous; sparsely branched above, or unbranched above. The branching simple. Culm nodes hairy, or glabrous. Culm internodes solid, or hollow. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate; without auricular setae. Leaf blades linear; narrow; flat, or folded, or rolled; not pseudopetiolate; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane; truncate. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality. Plants exposed-cleistogamous, or chasmogamous; with hidden cleistogenes, or without hidden cleistogenes. The hidden cleistogenes when present, in the leaf sheaths.

Inflorescence. Inflorescence paniculate, or of spicate main branches (the primary branches sometimes simple); open; with capillary branchlets, or without capillary branchlets; non-digitate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund, or not secund; pedicellate.

Female-fertile spikelets. Spikelets unconventional (the dilated pedicel apices may or may not represent ‘glumes’, the palea may ‘really’ be a lemma, etc. - c.f. Oryza); 3–6 mm long; suborbicular, or oblong, or elliptic, or ovate; strongly compressed laterally; disarticulating above the glumes (or at least, above the rim assumed to represent them); with no more than a short stipe beneath the floret, by contrast with Chikusichloa. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes absent (apparently represented by a narrow rim at the tip of the pedicel). Spikelets with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1. Lemmas not becoming indurated (membranous to papyraceous); awnless to awned (often caudate). Awns when present, 1; median; apical; non-geniculate; much shorter than the body of the lemma to much longer than the body of the lemma. Lemmas usually hairy (hispid on the nerves); carinate; without a germination flap; 3–5 nerved. Palea present; relatively long (but much narrower than the lemma); entire; awnless, without apical setae; tough; several nerved (3); one-keeled. Lodicules present; 2; free; fleshy, or membranous; glabrous; not toothed; heavily vascularized. Stamens 1–3, or 6. Anthers 0.5–2.4 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed laterally. Hilum long-linear. Embryo small; not waisted. Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins overlapping.

Seedling with a short mesocotyl, or with a long mesocotyl. First seedling leaf without a lamina.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal. Intercostal papillae over-arching the stomata; several per cell. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 22–30 microns long (L. hexandra), or 32–42 microns long (L. oryzoides); (3.9–)4.2–5.7 microns wide at the septum. Microhair total length/width at septum 4.7–7.1. Microhair apical cells 10–16 microns long (L. hexandra), or 16–24 microns long (L. oryzoides). Microhair apical cell/total length ratio 0.52–0.54. Stomata common; in L. hexandra, 22–30 microns long. Subsidiaries papillate; triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; silicified, or not silicified. Intercostal silica bodies where present, crescentic, or tall-and-narrow, or oryzoid-type, or cross-shaped, or oryzoid-type. Costal short-cells conspicuously in long rows. Costal silica bodies oryzoid; sharp-pointed (with ‘corners’), or not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; traversed by columns of colourless mesophyll cells, or not traversed by colourless columns; with arm cells, or without arm cells; without fusoids. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib conspicuous, or not readily distinguishable; with one bundle only, or having complex vascularization (rarely); with colourless mesophyll adaxially (rarely), or without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups (in the furrows); in simple fans (L. hexandra), or associated with colourless mesophyll cells to form deeply-penetrating fans (L. oryzoides). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Culm anatomy. Culm internode bundles in one or two rings.

Phytochemistry. Leaves without flavonoid sulphates (1 species).

Cytology. Chromosome base number, x = 12. 2n = 24, 48, and 60. 2, 4, and 5 ploid. Chromosomes ‘small’.

Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Oryzeae. Soreng et al. (2015): Oryzoideae; Oryzeae; Oryzinae. 18 species.

Distribution, phytogeography, ecology. Tropical and warm temperate.

Commonly adventive. Helophytic; shade species and species of open habitats.

Economic aspects. Significant weed species: L. hexandra (in rice), L. oryzoides. Important native pasture species: L. hexandra.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis, Puccinia striiformis, and Puccinia recondita. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Tilletia. Ustilaginaceae — Sorosporium, Tolyposporium, and Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; this project.

Illustrations. • L. oryzoides, general aspect: Eng. Bot. (1872). • General aspect (L. hexandra): Gibbs Russell et al., 1990. • Inflorescence detail (L. hexandra). • L. hexandra, abaxial epidermis of leaf blade: this project. • L. hexandra, abaxial epidermis of leaf blade: this project. • L. hexandra, abaxial epidermis of leaf blade, detailing silica bodies: this project


We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.


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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