The grass genera of the world
Including Houzeaubambus Mattei, Scirpobambus Kuntze
Habit, vegetative morphology. Arborescent shrubby perennial; caespitose. The flowering culms leafy (but the culm leaves deciduous). Culms 300–1300 cm high (somewhat crooked, bending over to the ground); woody and persistent (forming dense clumps); to 10 cm in diameter; cylindrical; branched above (at the nodal line). Primary branches 11–20; in an irregular line. The branching dendroid. Culm nodes glabrous. Culm leaf sheaths present; deciduous; not conspicuously auriculate. Culm leaves with conspicuous blades. Culm leaf blades linear. Culm internodes solid, or hollow. Pluricaespitose. Rhizomes pachymorph. Plants unarmed. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate; with auricular setae (these deciduous). Leaf blades linear-lanceolate to lanceolate; broad; 10–30 mm wide; flat; pseudopetiolate; without cross venation; disarticulating from the sheaths. Ligule an unfringed membrane; truncate; 0.3–0.5 mm long. Contra-ligule present, or absent (e.g., O. abyssinica).
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (there being numerous sterile spikelets); hermaphrodite and sterile.
Inflorescence. Inflorescence indeterminate; with pseudospikelets; a false spike, with spikelets on contracted axes (the clusters sometimes confluent or reduced to a single terminal cluster like that of female Spinifex); spatheate (each spikelet cluster subtended by a papery sheath, and individual spikelets by several short, papery bracts); not comprising partial inflorescences and foliar organs. Spikelet-bearing axes capitate. Spikelets associated with bractiform involucres.
Female-fertile spikelets. Spikelets unconventional; 15–45 mm long; lanceolate; compressed laterally to not noticeably compressed; falling with the glumes; not disarticulating between the florets. Rachilla terminated by a female-fertile floret; hairless. Hairy callus absent.
Glumes two (cross-veined); very unequal; shorter than the adjacent lemmas; hairy (shortly hispidulous); pointed, or not pointed (obtuse to acute); awnless; non-carinate; similar (papery to leathery). Lower glume much shorter than half length of lowest lemma; 17–30 nerved. Upper glume 17–30 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1–3; male, or sterile (the paleas when present two-keeled). The proximal lemmas awned, or awnless (then mucronate); 26–32 nerved; exceeded by the female-fertile lemmas; similar in texture to the female-fertile lemmas; not becoming indurated.
Female-fertile florets 1. Lemmas similar in texture to the glumes (papery to thinly leathery); not becoming indurated; entire; pointed; mucronate to awned. Awns 1; median; apical; non-geniculate; to 7 mm long. Lemmas hairy (hispid); non-carinate; without a germination flap; 11–23 nerved (with cross-nerves). Palea present; relatively long (may exceed the lemma); convolute around the flower; entire (pointed); awnless, without apical setae; not indurated; several nerved (16–19); keel-less (convolute). Lodicules absent. Stamens 6; monadelphous. Anthers not penicillate; with the connective apically prolonged. Ovary apically glabrous (but the style mostly shortly hairy); with a conspicuous apical appendage. The appendage long, stiff and tapering. Styles fused (the ovary attenuate into the single, hollow style). Stigmas 3.
Fruit, embryo and seedling. Fruit free from both lemma and palea; large; not noticeably compressed. Hilum long-linear. Embryo small. Endosperm containing compound starch grains.
Seedling with a short mesocotyl; with a loose coleoptile. First seedling leaf without a lamina.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae over-arching the stomata; several per cell. Long-cells markedly different in shape costally and intercostally; differing markedly in wall thickness costally and intercostally. Mid-intercostal long-cells having markedly sinuous walls. Microhairs present; panicoid-type; 42–46.5 microns long; 5.4–6 microns wide at the septum. Microhair total length/width at septum 7–8.8. Microhair apical cells 21–24 microns long. Microhair apical cell/total length ratio 0.45–0.52. Stomata common; 27–30 microns long. Subsidiaries low to high dome-shaped, or triangular. Intercostal short-cells absent or very rare. Costal short-cells predominantly paired. Costal silica bodies saddle shaped and oryzoid; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade; without arm cells; with fusoids. The fusoids external to the PBS. Leaf blade adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; having complex vascularization. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures. Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 12. 2n = 72. 6 ploid.
Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Bambuseae. Soreng et al. (2015): Bambusoideae; Bambusodae; Bambuseae; Bambusinae. 1 species (O. abyssinica).
Distribution, phytogeography, ecology. Africa.
Mesophytic; shade species; glycophytic. Growing in the protection of larger trees.
Economic aspects. O. abyssinica stems used for light construction and fencing.
Rusts and smuts. Rusts Dasturella. Taxonomically wide-ranging species: Dasturella divina.
References, etc. Leaf anatomical: Metcalfe 1960.
Illustrations. • O. abyssinica Fl. W. Trop. Afr. (1936). • General structure (O. abyssinica): Gibbs Russell et al., 1990
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: 11th December 2017. delta-intkey.com/grass’.