| # The grass genera of the world |

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

### Swallenochloa McClure

Named for J.R. Swallen, agrostologist.

~ Chusquea

Habit, vegetative morphology. Perennial. The flowering culms leafy. Culms woody and persistent; scandent; branched above. Culm internodes hollow (‘or pith breaking down’). Unicaespitose. Rhizomes pachymorph. Plants unarmed. Young shoots intravaginal. Leaves not basally aggregated; auriculate (the auricles small), or non-auriculate; without auricular setae. Leaf blades broad; pseudopetiolate; cross veined; disarticulating from the sheaths; rolled in bud. Contra-ligule present, or absent.

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

Inflorescence. Inflorescence determinate; paniculate (terminating the culm in addition to leafy or leafless lateral shoots); contracted; spicate (the lateral branches appressed); spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes paniculate; persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 5–9 mm long; compressed laterally (?); disarticulating above the glumes; disarticulating between the florets (beneath the fertile lemma). Rachilla terminated by a female-fertile floret.

Glumes two; minute, or relatively large; very unequal; shorter than the adjacent lemmas; not pointed (blunt); awnless; non-carinate; similar. Lower glume much shorter than half length of lowest lemma. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 2; sterile. The proximal lemmas awnless (with a very short subule); exceeded by the female-fertile lemmas, or exceeded by the female-fertile lemmas to more or less equalling the female-fertile lemmas; similar in texture to the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas not becoming indurated; entire; pointed; mucronate. Palea present; relatively long; apically notched; awnless, without apical setae, or with apical setae; not indurated; several nerved; 2-keeled to keel-less (being keeled only near tip). Lodicules present; 3; free; membranous; ciliate; not toothed; heavily vascularized. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles fused (the ovary attenuate). Stigmas 2.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (and the intercostal zones with a median astomatal zone). Papillae present; costal and intercostal (but conspicuously absent from the median, astomatal intercostal regions). Intercostal papillae over-arching the stomata; several per cell (12–20 small, thick walled, lobed or branching papillae per long-cell, in two or three iregular rows). Long-cells similar in shape costally and intercostally to markedly different in shape costally and intercostally (those the costal zones much smaller); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type; 39–45 microns long; 6.6–10.5 microns wide at the septum. Microhair total length/width at septum 3.7–6.8. Microhair apical cells 18–24 microns long. Microhair apical cell/total length ratio 0.45–0.55. Stomata common; 27–30 microns long. Subsidiaries papillate (often with two on each). Intercostal short-cells common (in the astomatal regions); in cork/silica-cell pairs; silicified. Intercostal silica bodies crescentic. Macrohairs and prickles lacking in the material seen. Crown cells absent. Costal short-cells conspicuously in long rows. Costal silica bodies predominantly saddle shaped and oryzoid; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. 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 (broad, flat topped). Midrib conspicuous; having complex vascularization. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (a conspicuous group in each furrow); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (the minor bundles with slender I’s, the primary bundles with ‘anchors’). Sclerenchyma all associated with vascular bundles.

Cytology. 2n = 40.

Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Bambuseae. Soreng et al. (2015): Bambusoideae (as a synonym); Bambusodae; Bambuseae; Chusqueinae. 5 species.

Distribution, phytogeography, ecology. Bolivia and Brazil to Costa Rica.

References, etc. Morphological/taxonomic: Soderstrom 1978; Soderstrom and Calderón 1978b. Leaf anatomical: studied by us - S. longiligulata Soderstrom & Calderon.

Special comments. Fruit data wanting.

Illustrations. • Swallenochloa tessellata: McClure, New World Bamboos (1973). • Swallenochloa longiligulata, abaxial epidermis of leaf blade: 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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