| # The grass genera of the world |

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

### Mnesithea Kunth

Named after the Greek herbalist, Mnesitheus.

Including Dipterum Desv., Thyridostachyum Nees

Excluding Hackelochloa, Heteropholis, Coelorachis

Habit, vegetative morphology. Perennial; caespitose. Culms 50–170 cm high; herbaceous; sparsely to amply branched above. The branching simple. Culm internodes solid. Leaves non-auriculate. Leaf blades broad, or narrow; 5–25 mm wide; flat, or rolled (finally involute); not pseudopetiolate; without cross venation. Ligule present; an unfringed membrane; truncate; short.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and sterile; overtly heteromorphic (the pedicelled members reduced to the two glumes, or vestigial); all in heterogamous combinations.

Inflorescence. Inflorescence of subterete, spike-like ‘racemes’; non-digitate. Rachides hollowed. Inflorescence spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes spikelike; solitary; with substantial rachides; disarticulating; disarticulating at the joints. ‘Articles’ non-linear (shortly clavate, concave, with embedded sessile spikelets and cupuliform apices); with a basal callus-knob; not appendaged; disarticulating transversely (the cupuliform apex fitting the basal knob of the next higher joint); glabrous (sometimes striate). Spikelets in triplets (2 sessile, 1 pedicelled in the lower part of the spikelike ‘raceme’), or paired (towards the tips, or throughout depauperate racemes); secund (the sessile members in two alternating rows, on one side of the dorsiventral rachis); sessile and pedicellate (the pedicels slender). Pedicel apices cupuliform. Spikelets consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets discernible, but fused with the rachis (in association with spikelet pairs, towards the inflorescence tips), or free of the rachis (with the triplets). The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets sterile (reduced to two minute glumes, or rudimentary).

Female-sterile spikelets. The pedicelled spikelet very greatly reduced or vestigial.

Female-fertile spikelets. Spikelets 3.5–4.5 mm long; abaxial (the G2 embedded in rachis); compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes present; two; more or less equal; long relative to the adjacent lemmas; free; dorsiventral to the rachis; hairy (e.g., M. mollicoma, with tubercle-based short white hairs), or hairless; without conspicuous tufts or rows of hairs; awnless; non-carinate; very dissimilar (G1 obliquely ovate with narrowly incurved margins, indurated, the G2 convex and much thinner). Lower glume not two-keeled; convex on the back, or flattened on the back; not pitted; relatively smooth, or tuberculate. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 2 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas oblong; less firm than the glumes (hyaline); not becoming indurated; entire; pointed, or blunt; awnless; hairless; non-carinate; without a germination flap; 3 nerved. Palea present; awnless, without apical setae; not indurated (hyaline); 2-nerved, or nerveless; keel-less. Lodicules present; free; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit compressed dorsiventrally.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells of similar wall thickness costally and intercostally. Intercostal zones exhibiting many atypical long-cells (many very short ones). Mid-intercostal long-cells rectangular (in M. laevis, many long-cells are almost square); having markedly sinuous walls (exaggeratedly so in M. laevis). Microhairs present; panicoid-type (but relatively broad in laevis); 45–54 microns long (M. laevis), or 69–84 microns long (M. mollicoma); 8.4–11.4 microns wide at the septum (M. laevis), or 5.4–6.6 microns wide at the septum (M. mollicoma). Microhair total length/width at septum 4.2–5.4 (M. laevis), or 10.4–15.6 (M. mollicoma). Microhair apical cells 25.5–39 microns long (M. laevis), or 39–51 microns long (M. mollicoma). Microhair apical cell/total length ratio 0.57–0.62 (M. laevis), or 0.5–0.63 (M. mollicoma). Stomata common; 54–63 microns long (M. laevis), or 30–33 microns long (M. mollicoma). Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified (M. laevis), or not silicified. Intercostal silica bodies when present, oryzoid-type. Cushion-based macrohairs present in M. mollicoma. Costal short-cells predominantly paired. Costal silica bodies oryzoid (all, in M.laevis), or ‘panicoid-type’ (M. mollicoma); not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS– (but occasional cells in ms position in M. laevis). Leaf blade ‘nodular’ in section. Midrib conspicuous (a smaller primary bundle in M. laevis with the closely opposed hinge-cells forming a single bulliform group above it, conventional in M. mollicoma); having a conventional arc of bundles (a median keel bundle and several small laterals); with colourless mesophyll adaxially (over the midrib in M. mollicoma, over the primary bundles except the midrib in M. laevis). Bulliforms not present in discrete, regular adaxial groups (the epidermis of large cells); associating with colourless mesophyll cells to form arches over small vascular bundles. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries); nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 9. 2n = 18. 2 ploid.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. 5 species.

Distribution, phytogeography, ecology. India, Ceylon to Southeast Asia.

Mesophytic. Damp grassland.

Rusts and smuts. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium and Sphacelotheca.

References, etc. Leaf anatomical: studied by us - iM. laevis (Retz.) Kunth, M. mollicoma (Hance) A. Camus.

Special comments. Fruit data wanting.

Illustrations. • Mnethisea formosa: Gardner, 1952. • Inflorescence triplets in lateral view of inflorescence (M. mollicoma). • Inflorescence detailing spikelet triplets (Mnesithea mollicoma). Mnesithea mollicoma. Triplets of spikelets at each node: two sessile, hermaphrodite, abaxial (tuberculate G1 and flimsy G2), and one free-pedicellate (sterile, reduced). • Inflorescence detail showing reduced triplets (Mnesithea laevis). Mnesithea laevis. A triplet of spikelets at each node. Two sessile (hermaphrodite), abaxial, with smooth G1; and a pedicellate one, much reduced and scarcely reconisable as such, its pedicel fused with the rachis. • Mnesithea laevis, abaxial epidermis of leaf blade: 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: 15th June 2025. delta-intkey.com’.

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