| # The grass genera of the world |

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

### Atractantha McClure

Habit, vegetative morphology. Perennial. The flowering culms leafy. Culms woody and persistent; branched above. Buds from which the primary culm branches arise (where recorded) 1. Primary branches (1–)2–20; sometimes horizontally aligned. The branching dendroid. Culm nodes glabrous. Culm leaf sheaths present; deciduous; leaving a persisten girdle; conspicuously auriculate, or not conspicuously auriculate. Culm leaves with conspicuous blades. Culm leaf blades linear, or lanceolate, or triangular. Culm internodes solid, or hollow. Plants unarmed. Leaves not basally aggregated; auriculate (the auricles usually very weakly developed); with auricular setae. Leaf blades broad, or narrow; pseudopetiolate; without cross venation; disarticulating from the sheaths, or persistent (but demarcated); rolled in bud. Ligule an unfringed membrane; truncate; 1 mm long (or less). Contra-ligule present, or absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. Not viviparous.

Inflorescence. Inflorescence indeterminate; with pseudospikelets; either capitate or diffuse, the branching pattern either distichous or sympodial, each axis representing the bracteate or prophyllate rachis of a pseudospikelet, the terminal segment of each rachis serving as the pedicel of an abscissile pseudospikelet; spatheate (at least, ‘bracteate’ or prophyllate); not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes paniculate to capitate; persistent. ‘Articles’ glabrous. Spikelets solitary; not secund.

Female-fertile spikelets. Spikelets unconventional (fairly, though the palea and lemma are recognizable in the pseudospikelet); 15–17 mm long; lanceolate, or linear; not noticeably compressed; disarticulating above the glumes (immediately below the lemma). Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes absent (the spikelet subtended by a small prophyll, but no sterile bracts). Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.

Female-fertile florets 1. Lemmas attenuately acuminate; not becoming indurated; entire; pointed; hairless; non-carinate; without a germination flap. Palea present; relatively long; convolute around the flower; apically notched to deeply bifid; awnless, without apical setae; not indurated; 2-keeled (with a narrow sulcus, or tubular). Lodicules present; 3; free; fleshy; ciliate; not toothed; heavily vascularized. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically hairy (antrorsely hispidulous); without a conspicuous apical appendage. Styles fused. Stigmas 2(–3).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal. Intercostal papillae over-arching the stomata (and obscuring them); several per cell (mostly with a single, median row of large, circular or bifurcated papillae per long-cell). Long-cells similar in shape costally and intercostally to markedly different in shape costally and intercostally (the intercostals often shorter and wider); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type; 51–79.5 microns long; 9.6–10.5 microns wide at the septum. Microhair total length/width at septum 4.9–7.6. Microhair apical cells 21–42 microns long. Microhair apical cell/total length ratio 0.4–0.55. Stomata common; 30–33 microns long. Guard-cells overlapped by the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies saddle shaped to oryzoid-type (cf. the costals). Costal short-cells predominantly paired. Costal silica bodies saddle shaped (a tall, narrowish form of these predominating), or oryzoid (sometimes with some of the saddles approaching this form).

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 the ribs more or less constant in size (low and flat-topped, save for a tall, narrow rib near one leaf margin). Midrib not readily distinguishable; with one bundle only. The lamina distinctly asymmetrical on either side of the midrib, or symmetrical on either side of the midrib (depending on whether the submarginal rib represents a highly asymmetrically placed midrib). Bulliforms present in discrete, regular adaxial groups; in simple fans (the groups large). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (nearly all the bundles). Sclerenchyma not all bundle-associated (there being conspicuous abaxial groups opposite the bulliforms, and commonly small adaxial hypodermal arcs 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.

Special diagnostic feature. The inflorescences of very peculiar pseudospikelets, characterized by development of rachides with long terminal segments, each of which serves as the pedicel of an abscissile spikelet.

Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Bambuseae. Soreng et al. (2015): Bambusoideae; Bambusodae; Bambuseae; Arthrostylidiinae. 2 species.

Distribution, phytogeography, ecology. Brazil.

References, etc. Leaf anatomical: studied by us - A. falcata McClure.

Special comments. Fruit data wanting.

Illustrations. • Atractantha falcata: McClure (1973), Smiths. Contr. Bot. 9. • Atractantha falcata, abaxial epidermis of leaf blade with papillae in high level focus: this project. • A. falcata, abaxial epidermis of leaf blade: this project. • Atractantha falcata, TS of leaf blade: this project. • A. falcata, TS of leaf blade: this project. • A. radiata: MacClure (1973), Smiths. Contr. Bot. 9.

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