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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. • A. longiflorum, A. cubense, A. pubescens: Camus (1913). • Abbreviations for Camus (1913) figures. • A. multispicatum: Hitchcock (1936)


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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: 25th November 2016. delta-intkey.com’.

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