| # The grass genera of the world |

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

### Athroostachys Bentham

Habit, vegetative morphology. Perennial; rhizomatous. The flowering culms leafy. Culms woody and persistent; scandent; branched above. Primary branches 3; horizontally aligned. The branching dendroid. Culm leaf sheaths present. Culm internodes hollow. Unicaespitose. Rhizomes pachymorph. Plants unarmed. Leaves not basally aggregated; with auricular setae. Leaf blades lanceolate; broad; pseudopetiolate; without cross venation; disarticulating from the sheaths. Contra-ligule absent.

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

Inflorescence. Inflorescence determinate; paniculate; contracted; capitate; spatheate (bracteate, the lower bracts liguliform caudate and foliar up to 3 cm long, the upper being short awned scales 0.5 mm long); not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets readily interpreted, provided the subtending bracts are not regarded as glumes; 10–15 mm long; lanceolate; compressed laterally; disarticulating above the glumes; not disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two; very unequal; shorter than the adjacent lemmas; pointed; awned; similar. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets without proximal incomplete florets.

Female-fertile florets 1. Lemmas entire; pointed; awnless to awned (?- subulate-acuminate); hairy (above). Palea present; relatively long; not convolute; awnless, without apical setae; 2-nerved; 2-keeled. Lodicules present (their tips subulate-acuminate); 3; free; ciliate (towards their tips); not toothed; heavily vascularized. Stamens 3. Anthers not penicillate; with the connective apically prolonged (the thecae apiculate). Ovary apically glabrous; without a conspicuous apical appendage. Styles fused. Stigmas 2.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal. Intercostal papillae over-arching the stomata (and almost completely covering them); several per cell (most long-cells with a median row of conspicuous, quite large, mainly bifurcated papillae). 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; elongated; clearly two-celled; panicoid-type; 60–69 microns long; 8.4–10.5 microns wide at the septum. Microhair total length/width at septum 5.9–7.7. Microhair apical cells 27–33 microns long. Microhair apical cell/total length ratio 0.4–0.48. Stomata common; 24–28.5 microns long. Guard-cells sunken. Intercostal short-cells fairly common (in 291–295,2 places), or absent or very rare (elsewhere); not paired (solitary); not silicified (in the material seen). Large costal prickles present, mostly without basal rosettes. Crown cells absent. Costal short-cells predominantly paired (superposed, often ostensibly solitary). Costal silica bodies poorly developed (and few).

Transverse section of leaf blade, physiology. C3. Mesophyll without adaxial palisade; with arm cells; with fusoids. The fusoids external to the PBS. Leaf blade with distinct, prominent adaxial ribs, or adaxially flat (the ribs very low, wide and flat-topped to scarcely manifest). Midrib not readily distinguishable; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (between each bundle pair); in simple fans (the groups very large, with deeply penetrating median cells). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming ‘figures’ (some forming slender I’s or ‘anchors’). Sclerenchyma not all bundle-associated (there being small abaxial groups opposite the bulliforms, and adaxial hypodermal fibres lining their sides). The ‘extra’ sclerenchyma in abaxial groups and in adaxial groups; abaxial-hypodermal, the groups isolated and adaxial-hypodermal, contiguous with the bulliforms.

Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Bambuseae. Soreng et al. (2015): Bambusoideae; Bambusodae; Bambuseae. 1 species (A. capitata).

Distribution, phytogeography, ecology. Brazil.

References, etc. Leaf anatomical: studied by us - A. capitata (Hook.) Benth.

Special comments. Fruit data wanting.

Illustrations. • A. capitata: McClure, New World Bamboos (1973). • A. capitata, as Merostachys (with Merostachys spp.: Camus, 1913).. • abbreviations for Camus (1913) figures. • Athroostachys capitata, abaxial epidermis of leaf blade: this project. • A. capitata, abaxial epidermis of leaf blade: this project. • Athroostachys capitata, TS of leaf blade: this project. • A. capitata, TS of leaf blade, detail: 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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