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The grass genera of the world

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

Rehia Fijten

Including Bulbulus Swallen

Habit, vegetative morphology. Perennial; caespitose (the slender culms in small dense tufts). The flowering culms leafy. Culms 12–19 cm high; herbaceous; unbranched above; tuberous. Culm nodes hairy. Plants unarmed. Leaves not basally aggregated; without auricular setae. Leaf blades broad; 7–16 mm wide (and 2–4.5 cm long, acute); somewhat cordate, or not cordate, not sagittate (but rounded at the base); pseudopetiolate; cross veined.

Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only and male-only. The male and female-fertile spikelets mixed in the inflorescence. The spikelets overtly heteromorphic (the males smaller, glabrous).

Inflorescence. Inflorescence indeterminate (with synflorescences); few spikeleted, or many spikeleted; paniculate (panicles terminal, small, borne singly or several together, each of 2–5 spikelet pairs or triplets, scarcely exserted or partially enclosed in a sheath); spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes disarticulating. Spikelets in triplets (sometimes 1 female with 2 male), or paired; pedicellate; consistently in ‘long-and-short’ combinations; unequally pedicellate in each combination. The ‘shorter’ spikelets female-only. The ‘longer’ spikelets male-only.

Female-sterile spikelets. Male spikelets 5 mm long, the floret with 3 stamens. Rachilla of male spikelets terminated by a male floret. The male spikelets without glumes; without proximal incomplete florets; 1 floreted. Male florets 1; 3 staminate.

Female-fertile spikelets. Spikelets 7–8 mm long; lanceolate; with conventional internode spacings. Rachilla terminated by a female-fertile floret. Callus absent.

Glumes two; more or less equal; long relative to the adjacent lemmas; pointed (acute or acuminate, somewhat twisted); awnless; similar (papery). Lower glume 7 nerved. Upper glume 7 nerved. Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes (?); becoming indurated; entire; pointed; awnless, or mucronate (?); hairy (pilose); having the margins inrolled against the palea. Palea present. Stamens 0 (but sometimes with staminodes).

Fruit, embryo and seedling. Fruit medium sized (5.5 mm long). Endosperm containing compound starch grains.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (and the intercostal zones each with a median astomatal zone). Papillae present; intercostal. Intercostal papillae over-arching the stomata (from the adjoining long-cells and interstomatals); several per cell (two or three irregularly shaped papillae, of various sizes, per cell in the stomatal zone). Long-cells markedly different in shape costally and intercostally (the costals narrower); of similar wall thickness costally and intercostally (fairly thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (the sinuosity fairly coarse). Microhairs present; elongated; clearly two-celled; panicoid-type; 63–69 microns long; 5.4–6.9 microns wide at the septum. Microhair total length/width at septum 9.6–12.1. Microhair apical cells 28.5–33 microns long. Microhair apical cell/total length ratio 0.4–0.5. Stomata common (in broad intercostal bands adjacent to the costal zones); 19.5–21 microns long. Subsidiaries papillate (two on each, large and conspicuous); predominantly high dome-shaped, or triangular. Intercostal short-cells common (in the astomatal zones); in cork/silica-cell pairs; silicified. Intercostal silica bodies vertically elongated-nodular. Prickles and macrohairs absent in the material seen. Crown cells absent. Costal short-cells conspicuously in long rows. Costal silica bodies oryzoid (mainly), or ‘panicoid-type’ (a few); sometimes approaching Maltese cross shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without arm cells (? - seemingly, in the distorted material seen); with fusoids. The fusoids external to the PBS. Leaf blade adaxially flat. Midrib conspicuous (with a large, round-topped adaxial projection); having a conventional arc of bundles (3 or 5); with colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (a large, wide group in each intercostal zone); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (all the bundles with an I or an ‘anchor’). Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 10. 2n = 20 (‘Bulbulus nervatus’).

Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Olyreae. Soreng et al. (2015): Bambusoideae; Bambusodae; Olyreae; Olyrinae. 1 species (R. nervata).

Distribution, phytogeography, ecology. Brazil.

Mesophytic; shade species. In forest.

References, etc. Leaf anatomical: this project.

Special comments. Fruit data wanting. Illustrations. • R. nervata, 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: 13th November 2017. delta-intkey.com/grass’.

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