| # The grass genera of the world |

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

### Thysanolaena Nees

From the Greek thysanos (fringe) and chlaina (cloak), referring to a fringed upper lemma.

Including Myriachaeta Moritzi

Habit, vegetative morphology. Tufted perennial; reedlike. Culms 150–400 cm high; woody and persistent; branched above (shrubby). Culm internodes solid. Leaves not basally aggregated; auriculate, or non-auriculate. Leaf blades lanceolate (-acuminate); somewhat leathery; broad; (30–)40–70(–100) mm wide (up to 60 cm long); somewhat cordate (amplexicaul); flat; pseudopetiolate; cross veined; disarticulating from the sheaths; rolled in bud. Ligule an unfringed membrane, or a fringed membrane (minutely ciliolate); truncate (cartilaginous). Contra-ligule present.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence paniculate (large, with numerous tiny spikelets); open (contracted on the primary branches); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating (pedicels and ultimate branchlets disarticulating). Spikelets secund; pedicellate.

Female-fertile spikelets. Spikelets 1.2–1.8 mm long; compressed laterally (and somewhat asymmetric); disarticulating above the glumes and falling with the glumes (falling with the pedicels, but also disarticulating above the glumes); tardily disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret (ending in a flattened process 0.5 mm long, with a flattened tip). Hairy callus absent.

Glumes two; relatively large; very unequal to more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; not pointed (obtuse); awnless; non-carinate; similar (broadly oval, hyaline). Lower glume 0–1 nerved. Upper glume 0–1 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets, or both distal and proximal to the female-fertile florets (proximal incomplete floret always present, distal rudiment present or absent). The distal incomplete florets when present, merely underdeveloped. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas acuminate, glabrous; awnless (acuminate); 1–3 nerved; decidedly exceeding the female-fertile lemmas (equalling the spikelet); less firm than the female-fertile lemmas (membranous); not becoming indurated.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes; becoming indurated (firmer than the L1); entire; pointed; awnless, or mucronate; hairy; non-carinate; without a germination flap; 3 nerved. Palea present; conspicuous but relatively short; apically notched; awnless, without apical setae; not indurated (thin); 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 2–3. Anthers 0.8 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; ellipsoid, or subglobose; not noticeably compressed. Hilum short. Embryo large; not waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present (but very scarce in material seen: perhaps variable in frequency, cf. Phragmites?); panicoid-type. Stomata common. Subsidiaries low dome-shaped, or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies tall-and-narrow, or crescentic, or vertically elongated-nodular, or oryzoid-type. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, butterfly shaped, and dumb-bell shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade; with arm cells. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles. Bulliforms present in discrete, regular adaxial groups (between each bundle pair); consistently in simple fans (in the material seen, the fans large with a deeply penetrating median cell). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (most of the bundles with a smallish I or T). Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 11, or 12 (?).

Classification. Watson & Dallwitz (1994): Centothecoideae, Arundinoideae; Arundineae (?). Soreng et al. (2015): Panicoideae; Thysanolaeneae. 1 species (T. maxima, = T. latifolia).

Distribution, phytogeography, ecology. Tropical Asia.

Species of open habitats; glycophytic. On mountains.

Economic aspects. Important native pasture species: T. latifolia.

References, etc. Leaf anatomical: Metcalfe 1960, and studied by us.

Illustrations. • Thysanolaena maxima: Jacques-Félix, 1962. • Thysanolaena maxima, abaxial epidermis of leaf blade: this project. • Thysanolaena maxima, abaxial epidermis of leaf blade: this project. • Thysanolaena maxima, TS 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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