| # The grass genera of the world |

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

### Arthrostylidium Rupr.

Habit, vegetative morphology. Perennial; caespitose. The flowering culms leafy. Culms woody and persistent (the first culm internode often disproportionately elongated); scandent, or not scandent; branched above. Buds from which the primary culm branches arise 1. Primary branches (1–)2–20; clumped. The branching simple (rarely), or dendroid, or fastigiate (commonly). Culm leaf sheaths present (usually), or absent; deciduous (sometimes tardily so), or persistent; when present, commonly not conspicuously auriculate. Culm leaves with conspicuous blades. Culm leaf blades linear, or lanceolate, or ovate, or triangular. Unicaespitose. Rhizomes pachymorph. Plants unarmed. Leaves not basally aggregated; with auricular setae. Leaf blades pseudopetiolate; cross veined, or without cross venation; disarticulating from the sheaths, or persistent. Contra-ligule present, or absent (mostly).

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

Inflorescence. Inflorescence of spicate main branches (of spicate racemes); digitate, or subdigitate, or non-digitate (?); espatheate (with neither bracts nor prophylls); not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary.

Female-fertile spikelets. Spikelets lanceolate, or linear; compressed laterally; disarticulating above the glumes. 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; carinate (apparently); similar. Spikelets with incomplete florets. The incomplete florets both distal and proximal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets with proximal incomplete florets. The proximal incomplete florets 1. The proximal lemmas exceeded by the female-fertile lemmas.

Female-fertile florets 2–7 (‘few to several’). Lemmas entire; pointed; awnless, or mucronate, or awned. Awns when present, 1; non-geniculate; much shorter than the body of the lemma. Lemmas carinate. Palea present; not convolute; 2-nerved; 2-keeled (broadly sulcate). Lodicules nearly always present; 3; free; ciliate; not toothed; heavily vascularized. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous; with a conspicuous apical appendage. The appendage broadly conical, fleshy. Styles fused. Stigmas 2.

Fruit, embryo and seedling. Fruit longitudinally grooved; compressed dorsiventrally to not noticeably compressed. Hilum long-linear. Embryo small.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present, or absent. Long-cells of similar wall thickness costally and intercostally, or differing markedly in wall thickness costally and intercostally. Mid-intercostal long-cells having markedly sinuous walls. Microhairs present; panicoid-type. Stomata common. Subsidiaries low dome-shaped. Intercostal short-cells common (abundant); in cork/silica-cell pairs. Costal short-cells predominantly paired (and some short rows). Costal silica bodies saddle shaped.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with arm cells (these relatively inconspicuous); with fusoids (but these scarce). The fusoids external to the PBS. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section; with the ribs more or less constant in size, or with the ribs very irregular in sizes. Midrib conspicuous; having complex vascularization. Bulliforms present in discrete, regular adaxial groups; in simple fans (mostly), or associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (nearly all the bundles); forming ‘figures’.

Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Bambuseae. Soreng et al. (2015): Bambusoideae; Bambusodae; Bambuseae; Arthrostylidiinae. 20 species.

Distribution, phytogeography, ecology. New World.

References, etc. Leaf anatomical: Metcalfe 1960.

Illustrations. • Arthrostylidium cubense and A. multispicatum: McClure, New World Bamboos (1973). • A. longiflorum, A. cubense, A. pubescens: Camus (1913). • Abbreviations for Camus (1913) figures. • A. multispicatum: Hitchcock (1936).

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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