| # The grass genera of the world |

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

### Thyrsostachys Gamble

From the Greek thyrsos (a Bacchic wand), probably via the derived botanical term thyrse, and stachyus (relating to inflorescence), alluding to inflorescence form.

Habit, vegetative morphology. Arborescent perennial; caespitose. The flowering culms leafy. Culms 800–1000 cm high; woody and persistent; to 3–6 cm in diameter; branched above. Primary branches 11–20; horizontally aligned. The branching dendroid. Culm leaf sheaths present; persistent; not conspicuously auriculate. Culm leaves with conspicuous blades. Culm leaf blades linear, or triangular. Rhizomes pachymorph. Plants unarmed. Leaves not basally aggregated; auricles very small; with auricular setae (these small), or without auricular setae. Leaf blades broad; about 10–15 mm wide (by 7–18 cm long); pseudopetiolate; disarticulating from the sheaths; rolled in bud. Ligule an unfringed membrane. Contra-ligule absent.

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

Inflorescence. Inflorescence indeterminate; with pseudospikelets; paniculate (large, compound, thyrsoid, the branch nodes bearing sessile, spatheate clusters each of few pseudospikelets); spatheate (the spikelet groups in the axils of short sheaths); a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes paniculate; persistent. Spikelets not secund.

Female-fertile spikelets. Spikelets unconventional; 10–25 mm long; lanceolate, or ovate; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets.

Glumes one per spikelet, or two; very unequal; shorter than the spikelets; shorter than the adjacent lemmas; hairy; pointed; awnless; similar. Upper glume about 9 nerved (‘about 4 on either side’). Spikelets with incomplete florets. The incomplete florets both distal and proximal to the female-fertile florets. The distal incomplete florets merely underdeveloped (differing from Bambusa in the more reduced terminal floret). Spikelets with proximal incomplete florets. The proximal incomplete florets 1, or 2; paleate (the palea of the lowest floret deeply bifid). Palea of the proximal incomplete florets fully developed. The proximal incomplete florets male. The proximal lemmas awnless; exceeded by the female-fertile lemmas; similar in texture to the female-fertile lemmas.

Female-fertile florets 1. Lemmas papery; not becoming indurated; entire; pointed; awnless, or mucronate (?); hairy; many nerved. Palea present; relatively long; not convolute; apically notched (less cleft thn in the proximal floret); several nerved; 2-keeled (less clearly so than in the proximal florets). Lodicules present, or absent; when present, 1–3; free; membranous (narrow); ciliate; not toothed. Stamens 6. Anthers not penicillate; shortly with the connective apically prolonged. Ovary apically glabrous; with a conspicuous apical appendage. The appendage broadly conical, fleshy. Styles fused (into one, the base not hollow - thick, forming beak in fruit). Stigmas 3.

Fruit, embryo and seedling. Fruit medium sized (5 to 10 mm long); not noticeably compressed (cylindrical); smooth (glabrous). Hilum long-linear. Pericarp thick and hard (or at least, crustaceous); free, or fused (?). Embryo small (prominent). Endosperm containing compound starch grains.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present (papillae small, variously shaped). Intercostal papillae over-arching the stomata. Mid-intercostal long-cells having markedly sinuous walls (thin). Microhairs present; panicoid-type. Stomata common (obscured by papillae). Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies saddle shaped. Costal short-cells conspicuously in long rows. Costal silica bodies saddle shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with arm cells; with fusoids. Leaf blade ‘nodular’ in section. Midrib conspicuous; having complex vascularization. Bulliforms present in discrete, regular adaxial groups; in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (in the large bundles).

Cytology. Chromosome base number, x = 12. 2n = 72. 6 ploid.

Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Bambuseae. Soreng et al. (2015): Bambusoideae; Bambusodae; Bambuseae; Bambusinae. 2 species.

Distribution, phytogeography, ecology. Burma, Siam.

Rain forest.

References, etc. Leaf anatomical: Metcalfe 1960.

Illustrations. • Thyrsostachys oliverae: Gamble, Bambuseae of Br. India (1896). • T. siamensis: Gamble, Bambuseae of Br. India (1896). • T. siamensis, with Guaduella spp.: Camus, 1913. • Abbreviations for Camus (1913) figures.

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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