| # The grass genera of the world |

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

### Racemobambos Holttum

From the Latin racemus (branch or cluster) and Malay vernacular name bambu, referring to clustered spikelets.

Including Microcalamus Gamble, Neomicrocalamus Keng f.

Habit, vegetative morphology. Perennial. The flowering culms leafy. Culms woody and persistent; to 1 cm in diameter; scandent (or scrambling, slender); branched above. Primary branches 1 (rarely), or (3–)4–20. The branching dendroid. Culm leaf sheaths present; where recorded, deciduous; not leaving a persistent girdle; where recorded, not conspicuously auriculate. Culm leaves with conspicuous blades. Culm leaf blades linear (rarely), or lanceolate (commonly). Rhizomes pachymorph. Plants unarmed. Leaves not basally aggregated; auriculate (the auricles raised or not prominent); with auricular setae (these slender). Leaf blades narrow; 4–10 mm wide (‘to 1 cm’); pseudopetiolate; where recorded, disarticulating from the sheaths; rolled in bud. Contra-ligule consistently absent (including Neomicrocalamus).

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

Inflorescence. Inflorescence determinate; without pseudospikelets; a single raceme, or paniculate (of small terminal racemes or panicles, each spikelet subtended by a small bract); spatheate (not foliate, the bracts with or without a rudimentary blade); a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes ‘racemes’; solitary; persistent. Spikelets solitary; secund (‘all spikelets twisted to side of blade opposite subtending leaf’); more or less sessile; not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets 15–20 mm long; lanceolate (mostly), or elliptic, or linear (rarely); compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two, or several (2–3); very unequal (G1 shorter); shorter than the spikelets; shorter than the adjacent lemmas; free; pointed; awnless; non-carinate (G2 slightly keeled near tip); very dissimilar (G1 much narrower). Lower glume 1–3 nerved. Upper glume 9–11 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1; merely underdeveloped. Spikelets without proximal incomplete florets.

Female-fertile florets 2–6. Lemmas similar in texture to the glumes; entire; pointed; awnless, or mucronate, or awned (the apex setiform). Awns 1; median; apical; non-geniculate; much shorter than the body of the lemma (the setum about 3 mm long). Lemmas with fringed margins; non-carinate; 7–11 nerved (in material seen). Palea present; relatively long (but shorter than lemmas); not convolute; apically notched; several nerved (9 in material seen); 2-keeled. Palea keels scabrous, or hairy. Lodicules present; 3; free; membranous; ciliate, or glabrous. Stamens 6. Anthers 5 mm long; not penicillate; without an apically prolonged connective. Ovary apically hairy; with a conspicuous apical appendage (usually), or without a conspicuous apical appendage (very rarely). The appendage broadly conical, fleshy. Styles fused. Stigmas 3 (the ovary apex swollen, no hollow style).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present (costally and around the stomata only). Intercostal papillae over-arching the stomata; several per cell (often quite thick-walled, rather irregular). Long-cells of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (30–)39–45(–47) microns long; (6–)6.6–8.4(–9) microns wide at the septum. Microhair total length/width at septum 3.6–7.8. Microhair apical cells (18–)21–25.5(–28.5) microns long. Microhair apical cell/total length ratio 0.5–0.63. Stomata common (bordering the veins only, completely covered by papillae); 27–30–33 microns long. Intercostal short-cells common; in cork/silica-cell pairs (and solitary); silicified. Intercostal silica bodies crescentic and saddle shaped. Bulbous prickles with tiny points common. Crown cells absent. Costal short-cells conspicuously in long rows. Costal silica bodies saddle shaped (predominating), or oryzoid (quite common); not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade; with arm cells; with fusoids. The fusoids external to the PBS. Leaf blade the lamina flat to low-ribbed. Midrib conspicuous (via the large bundle and the prominent adaxial rib); with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming ‘figures’ (all bundles). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Bambuseae. Soreng et al. (2015): Bambusoideae; Bambusodae; Bambuseae; Racemobambosinae. About 16 species.

Distribution, phytogeography, ecology. Confined to Malesia, including Bismarck Archipelago and Solomon Islands.

References, etc. Morphological/taxonomic: Chao and Renvoise, 1989; Dransfield (1992: excludes taxa with pseudospikelets). Leaf anatomical: studied by us - R. gibbsiae (Stapf) Holttum.

Special comments. The status of the poorly known R. prainii (Gamble) Keng (= Arundinaria prainii, Microcalamus prainii, Neomicrocalamus Keng f.) is uncertain: see Dransfield (1992). Fruit data wanting.

Illustrations. • Racemobambos prainii (cf. Neomicrocalamus) and Pseudostachyum polymorphum: Yun nan zhi wuxhi(2003).

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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