The grass genera of the world
Habit, vegetative morphology. Perennial. The flowering culms leafy. Culms woody and persistent (slender, arborescent or scrambling); scandent to not scandent; branched above. Buds from which the primary culm branches arise (where recorded) 1. Primary branches 11–20; nearly always around a triangular space (clumped ony in R. ampliflorum). The branching dendroid. Culm leaf sheaths present; where recorded, deciduous. Culm leaves with conspicuous blades. Culm leaf blades where recorded, linear, or lanceolate, or triangular. Culm internodes hollow. Unicaespitose. Rhizomes pachymorph. Plants unarmed. Leaves not basally aggregated; with auricular setae. Leaf blades broad; pseudopetiolate; cross veined, or without cross venation; where recorded, 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 with axes ending in spikelets. Inflorescence spatheate; a complex of partial inflorescences and intervening foliar organs. Spikelet-bearing axes lax, spikes, or racemes; persistent. Spikelets solitary (usually), or paired; secund (the racemes unilateral), or not secund (the racemes bilateral, zigzag); sessile, or subsessile; not imbricate.
Female-fertile spikelets. Spikelets 20–60 mm long; lanceolate, or linear, or oblanceolate (commonly); compressed laterally (?); disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret.
Glumes two, or several (?); very unequal; shorter than the adjacent lemmas; awnless. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets, or both distal and proximal to the female-fertile florets. The distal incomplete florets merely underdeveloped. The proximal incomplete florets 1. The proximal lemmas awnless; exceeded by the female-fertile lemmas; similar in texture to the female-fertile lemmas; not becoming indurated.
Female-fertile florets 2–8 (? few to several). Lemmas similar in texture to the glumes; not becoming indurated; entire; pointed, or blunt; awnless. Palea present; not convolute; entire; awnless, without apical setae; not indurated; 2-keeled (and sulcate). Lodicules present; 3 (rarely 0–2); free; membranous; ciliate. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous; with a conspicuous apical appendage (rarely), or without a conspicuous apical appendage. The appendage when present, broadly conical, fleshy. Styles basally fused. Stigmas 2.
Fruit, embryo and seedling. Fruit longitudinally grooved, or not grooved. Hilum long-linear. Embryo small. Endosperm containing compound starch grains.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal (conspicuous, especially around the stomata and around the costal short-cells). Intercostal papillae over-arching the stomata; several per cell (most cells with one or two rows of circular papillae). Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type; 39–51 microns long; 6–8.4 microns wide at the septum. Microhair total length/width at septum 5.9–6.3. Microhair apical cells 21–27 microns long. Microhair apical cell/total length ratio 0.47–0.54. Stomata common; 24–28.5 microns long. Subsidiaries perhaps papillate, or it being hard to distinguish whether they come from the adjoining cells. Guard-cells overlapped by the interstomatals (the stomata and subsidiaries sunken, obscured by papillae). Intercostal short-cells common; not paired (in R. racemiflorum, and seemingly solitary but obscured by special quartets and rosettes of papillae in R. pittieri). Costal short-cells neither distinctly grouped into long rows nor predominantly paired (mostly seemingly solitary, obscured in R. pittieri by special papillae). Costal silica bodies absent, or poorly developed (in the material of the two species seen); (or at least, the silica cells) tall-and-narrow.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; with adaxial palisade to without adaxial palisade; without arm cells; with fusoids (conspicuous in both R. pittieri and R. racemiflorum, though less so in the latter and more easily detected towards the edges of the lamina). The fusoids external to the PBS. Leaf blade adaxially flat (except for a single adaxial rib near one margin). Midrib conspicuous; with one bundle only. The lamina symmetrical on either side of the midrib (unless the marginal rib be interpreted as a highly asymmetric midrib). Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present. Sclerenchyma not all bundle-associated. The extra sclerenchyma in abaxial groups and in adaxial groups; abaxial-hypodermal, the groups isolated and adaxial-hypodermal, contiguous with the bulliforms (there being groups of abaxial hypodermal fibres opposite the bulliforms, and adaxial groups or isolated fibres lining or adjoining them).
Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Bambuseae. Soreng et al. (2015): Bambusoideae; Bambusodae; Bambuseae; Arthrostylidiinae. 11 species.
Distribution, phytogeography, ecology. Central & South America.
References, etc. Leaf anatomical: studied by us - R. pittieri (Hack.) McClure, R. racemiflorum (Steud.) McClure.
Illustrations. • R. harmonicum, with fruit of Actinocladum verticillatum: McClure, New World Bamboos (1973). • R. parviflorum & R. racemiflorum (as Arthrostylidium trinii and A. racemiflorum, with A. capillifolium = A. farctum: Camus 1913). • Abbreviations for Camus (1913) figures
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’.