| # The grass genera of the world |

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

### Thyrsia Stapf

~ Phacelurus

Habit, vegetative morphology. Stout, reed-like, tall annual. Culms herbaceous. Leaf blades narrow; not setaceous; flat (long, hard); without cross venation. Ligule an unfringed membrane.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (heterogamous); hermaphrodite and male-only, or hermaphrodite and sterile (or the pedicellate spikelet rarely hermaphrodite); overtly heteromorphic, or homomorphic; in both homogamous and heterogamous combinations.

Inflorescence. Inflorescence of spicate main branches (with ‘racemes’ borne in terminal racemes or panicles); non-digitate. Rachides hollowed. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes spikelike (rather thick, cylindrical); with substantial rachides; disarticulating; disarticulating at the joints. ‘Articles’ non-linear (constricted and dilated); not appendaged; disarticulating transversely; glabrous. Spikelets paired; secund (the ‘racemes’ more or less dorsiventral); sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis (but contiguous). The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets usually male-only, or sterile (rarely hermaphrodite).

Female-sterile spikelets. The pedicellate spikelets usually sterile or male-only, sometimes reduced to their pedicels.

Female-fertile spikelets. Spikelets abaxial; compressed dorsiventrally; falling with the glumes (and the joint). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; more or less equal; long relative to the adjacent lemmas; dorsiventral to the rachis; hairless (glabrous, smooth); pointed; awnless; carinate (G2), or non-carinate (G1); very dissimilar (leathery or papery, the upper naviculate). Lower glume two-keeled; flattened on the back; not pitted; relatively smooth (shining). 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; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

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

Fruit, embryo and seedling. Fruit compressed dorsiventrally.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower and more regularly rectangular, the intercostals unusually large); of similar wall thickness costally and intercostally (of medium thickness). Mid-intercostal long-cells rectangular to fusiform; having markedly sinuous walls (the sinuosity quite fine, conspicuously pitted). Microhairs present; elongated; clearly two-celled; panicoid-type (rather large). Stomata common. Subsidiaries non-papillate; conspicuously triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies crescentic to tall-and-narrow. Bulbous prickles with tiny points common over the main veins. Costal short-cells predominantly paired. Costal silica bodies present and well developed to poorly developed; tall-and-narrow.

Transverse section of leaf blade, physiology. C4. The anatomical organization conventional. XyMS–. PCR sheath extensions absent. Mesophyll with radiate chlorenchyma. Leaf blade more or less adaxially flat (with very slight ribs over the primary bundles). Midrib conspicuous; having a conventional arc of bundles (a large, median primary with several smaller bundles on either side); with colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. Bulliforms not present in discrete, regular adaxial groups (the epidermis consisting of rather regular, large cells). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries only); forming ‘figures’ (slight I’s, in places, but the sclerenchyma scanty everywhere except in the large abaxial keel of the midrib). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae. 3–4 species.

Distribution, phytogeography, ecology. Tropical Africa, Asia.

References, etc. Morphological/taxonomic: Stapf 1922. Leaf anatomical: studied by us - T. inflata Stapf, T. undulatifolia (Chiov.) Robyns.

Illustrations. • Thyrsia undulatifolia: Jacques-Félix, 1962. • Thyrsia huillensis, as T. inflata: Hook. Ic. Pl. 31 (1922). • Thyrsia. undulatifolia, abaxial epidermis of leaf blade: this project. • Thyrsia undulatifolia, 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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