Grass Genera of the World

L. Watson 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/mid-culm node 3–20 (?-‘many’). Culm sheaths deciduous in their entirety. 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; disarticulating from the sheaths; rolled in bud.

Reproductive organization. Plants bisexual, 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; 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); 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 hairy; with a conspicuous apical appendage. 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.

Taxonomy. Bambusoideae; Bambusodae; Bambuseae.

Distribution, ecology, phytogeography. About 16 species; confined to Malesia, including Bismarck Archipelago and Solomon Islands.

Paleotropical. Indomalesian. Malesian and Papuan.

References, etc. Morphological/taxonomic: Chao and Renvoise, 1989; Dransfield (1992: excludes taxa with pseudospikelets). Leaf anatomical: this project.

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.


Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).

Index