| # The grass genera of the world |

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

### Actinocladum McClure ex Soderstrom

Name alluding to the manner of branching.

Habit, vegetative morphology. Perennial; caespitose. The flowering culms leafy. Culms 300–460 cm high; woody and persistent; to about 0.5–1.4 cm in diameter; branched above (and with rather different branches basally). Primary branches 10–20; around a triangular space. The branching dendroid. Culm leaf sheaths present; deciduous; leaving a persisten girdle; conspicuously auriculate. Culm leaves with conspicuous blades. Culm leaf blades lanceolate, or ovate. Culm internodes solid. Rhizomes pachymorph. Plants unarmed. Leaves not basally aggregated. Leaf blades broad; 10–40 mm wide; pseudopetiolate; disarticulating from the sheaths; rolled in bud. Ligule present; a minute ciliolate rim. Contra-ligule present.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality.

Inflorescence. Inflorescence determinate; consisting of verticils of racemose or paniculate, few-flowered ‘inflorescences’; spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs (with a spatheole at the first node of each ultimate inflorescence unit). Spikelet-bearing axes ‘racemes’, or paniculate; clustered; persistent. Spikelets not secund; long pedicellate.

Female-fertile spikelets. Spikelets 60–75 mm long; slightly compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairy (short-pilose); the rachilla extension with incomplete florets. Hairy callus present (of short hairs).

Glumes two; very unequal; shorter than the adjacent lemmas; free; hairless; glabrous; pointed; awnless (apiculate); non-carinate (rounded on the back); similar (leathery, triangular). Lower glume relatively smooth; 5 nerved. Upper glume 11 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.

Female-fertile florets 7–10. Lemmas ovate lanceolate; less firm than the glumes; not becoming indurated; entire; pointed; awnless; hairless; glabrous; non-carinate (rounded on the back); 13 nerved. Palea present; relatively long; minutely apically notched; awnless, without apical setae; not indurated; several nerved (6 between the keels, 5 on each wing); 2-keeled. Lodicules present; 3; free; membranous; ciliate, or glabrous; toothed; heavily vascularized. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically hairy; with a conspicuous apical appendage. The appendage broadly conical, fleshy. Styles fused (the top of the ovary being attenuate into a single style). Stigmas 2.

Fruit, embryo and seedling. Fruit large; not grooved (but the seed within it slightly grooved); slightly curved, compressed dorsiventrally; with hairs confined to a terminal tuft. Hilum long-linear. Pericarp dry, thick and hard; free. Embryo small.

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 (basically one median row per long-cell, large, thick walled, irregular, warty and sometimes bifurcated or branching). Intercostal zones probably with typical long-cells (but their shapes largely obscured but papillae, and hard to determine). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; mostly clearly two-celled (but occasionally with an extra, short basal cell); panicoid-type; 40–48 microns long; 5.4–6 microns wide at the septum. Microhair total length/width at septum 7.5–8. Microhair apical cells 18–25.3 microns long. Microhair apical cell/total length ratio 0.44–0.53. Stomata common; 22.5–27 microns long. Guard-cells sunken. Intercostal short-cells absent or very rare. Numerous large costal prickles present, with abundant tiny pits and conspicuous basal rosettes. Crown cells absent. Costal short-cells predominantly paired. Costal silica bodies absent (in the material seen).

Transverse section of leaf blade, physiology. C3. Mesophyll with adaxial palisade; with arm cells; with fusoids. The fusoids external to the PBS. Leaf blade with distinct, prominent adaxial ribs (with one large rib and a short series of smaller ones, near one margin), or adaxially flat (elsewhere). Midrib not readily distinguishable (unless the submarginal rib represents a highly asymmetrical midrib); with one bundle only. The lamina symmetrical on either side of the midrib (unless the large submarginal rib is interpreted as a highly asymmetrically placed midrib). Bulliforms present in discrete, regular adaxial groups (between all the adjoining veins); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (all the bundles with narrow I’s or ‘anchors’). Sclerenchyma not all bundle-associated. The ‘extra’ sclerenchyma in abaxial groups and in adaxial groups; abaxial-hypodermal, the groups isolated and adaxial-hypodermal, contiguous with the bulliforms (there being small abaxial groups opposite the bulliforms, and adaxial hypodermal fibres adjoining and lateral to them).

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

Distribution, phytogeography, ecology. Central Brazil.

References, etc. Morphological/taxonomic: Soderstrom 1981d. Leaf anatomical: studied by us.

Illustrations. • Actinocladum verticillatum, as Arundinaria: Kunth (1835). • A. verticillatum (as Arundinaria: Camus, 1913).. • Abbreviations for Camus (1913) figures. • Actinocladum verticillatum, abaxial epidermis of leaf blade: this project. R.S.B.S. Taxonomy Laboratory (Canberra) slide. Slides and full details now housed at the Western Australian Herbarium. • A. verticillatum, abaxial epidermis of leaf blade (papillae and prickles): this project. R.S.B.S. Taxonomy Laboratory (Canberra) slide. Slides and full details now housed at the Western Australian Herbarium.

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’.

Contents