The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose (in dense clumps). The flowering culms leafless (the culms dimorphic. Vegetative, with internodes not elongated, erect, with bladeless sheaths at the base, the uppermost of these to 20 cm long and clasping the solitary, terminal blade-bearing leaf. Reproductive culms with the internodes short below and much elongated above, all with bladeless sheaths). Culms 50–350 cm high; herbaceous; unbranched above. Culm internodes of the fertile culms hollow. Plants unarmed. Leaves not clearly differentiated into sheath and blade (in that the single developed leaf has no ligule, and the long, terete petiolar region gradually opens into the flattened laminar part); non-auriculate. Sheath margins joined, or free (depending on interpretation of the highly peculiar sheath of the solitary leaf, which is solid, cylindrical and stemlike, with two concentric rings of vascular bundles and numerous lacunae). Leaf blades linear; narrow; 2.8–6.5 mm wide; flattened, with plano-convex laminae flanking a narrow midrib, the distal 1–2 cm of the blades fused into a blunt, navicular tip; pseudopetiolate (or petiolate!); without cross venation; persistent. Ligule absent (i.e., the single complete leaf eligulate).
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite, female-only, and male-only (male or bisexual at the base of the inflorescence, bisexual in the middle, female towards the tip). The male and female-fertile spikelets segregated, in different parts of the same inflorescence branch. The spikelets overtly heteromorphic (see below).
Inflorescence. Inflorescence a single raceme (7–50 cm long, exserted-pedunculate, spicate, the spikelets densely arranged in irregular whorls, irregularly spiralled near the base); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes solitary; persistent. Spikelets not secund; shortly pedicellate; imbricate.
Female-sterile spikelets. Basal male spikelets dorsally compressed to terete, 4.5–7.7 mm long, with 2 or 3 florets, 2 functionally male, the uppermost rudimentary. Rachilla of male spikelets prolonged beyond the uppermost male floret. The male spikelets without proximal incomplete florets; 2–3 floreted. Male florets 2.
Female-fertile spikelets. Spikelets 4.5–7.5 mm long (bisexual spikelets), or 9–17 mm long (female spikelets); not noticeably compressed to compressed dorsiventrally; falling with the glumes. Rachilla prolonged beyond the uppermost female-fertile floret. Hairy callus absent.
Glumes two; more or less equal; shorter than the adjacent lemmas; hairless; not pointed (obtuse or truncate); awnless; non-carinate; very dissimilar (G1 2-keeled, hardened and thickened, G2 rounded on the back or slightly flattened). Lower glume two-keeled; 3–7 nerved. Upper glume 3–6 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets, or both distal and proximal to the female-fertile florets (always with a distal rudimentary floret, the lower floret usually male in bisexual spikelets, sterile in female spikelets). The distal incomplete florets merely underdeveloped. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; male (in bisexual spikelets), or sterile (sterile in female spikelets). The proximal lemmas awnless; 3–7 nerved (in bisexual spikelets), or 5–9 nerved (in female spikelets); similar in texture to the female-fertile lemmas (herbaceous); not becoming indurated.
Female-fertile florets 1 (or occasionally L1 and L2 both bisexual in the bisexual spikelets). Lemmas not becoming indurated; entire; pointed (broadly acute in bisexual spikelets), or blunt (in female spikelets); awnless; hairless; non-carinate; 3–7 nerved (in bisexual spikelets), or 5–11 nerved (in female spikelets). Palea present; relatively long (about equalling the lemma in bisexual spikelets. In female spikelets much exceeding it, curved, somewhat twisted and convolute, the apex forming a distinct oriface for the stigmas); convolute around the flower; awnless, without apical setae; membranous in bisexual spikelets, conspicuously spongy-thickened except for the herbaceous tip and membranous apex in female spikelets; 2-nerved (or more, in bisexual spikelets), or several nerved (5–11 in female spikelets); 2-keeled, or keel-less. Palea keels wingless. Lodicules absent. Stamens 2 (and posterior, in bisexual florets), or 0 (female florets with two posterior staminodes); with free filaments to monadelphous (the filaments free or fused along their length). Anthers 2.2–3.8 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles fused (the ovary attenuate into a short joint style in bisexual florets, into a long one in female florets). Stigmas 2.
Fruit, embryo and seedling. Fruit medium sized (about 5 mm long); fusiform; not noticeably compressed. Hilum long-linear. Embryo small (about 1/5 as long as the grain).
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls (the anticlinal walls thick and pitted). Microhairs absent. Stomata common. Subsidiaries dome-shaped. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies irregularly rounded. Costal short-cells predominantly paired. Costal silica bodies poorly developed; crescentic and oryzoid (but unclearly defined); not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade; without arm cells; without fusoids (but interrupted by a series of large, symmetrically-disposed lacunae, which separate the two rows of vascular bundles into vertically aligned pairs of bundles). Leaf blade adaxially flat. Midrib conspicuous (comprising a narrow median zone, separated from the thickened laminar flanges by large bulliform hinges); with one bundle only. Bulliforms absent, except for the midrib hinges. All the vascular bundles accompanied by sclerenchyma.
Special diagnostic feature. Culms dimorphic, the fertile culms leafless, the vegetative culms each with a single developed leaf, this being eligulate and with a terete, culm-like sheath.
Classification. Watson & Dallwitz (1994): Arundinoideae (or Bambusoideae?); Steyermarkochloeae. Soreng et al. (2015): Panicoideae; Steyermarkochloeae. 1–2 species (synonyms of S. angustifolia).
Distribution, phytogeography, ecology. Venezuela and Colombia.
Helophytic. Stream margins in savanna.
References, etc. Morphological/taxonomic: Davidse and Ellis 1984. Leaf anatomical: this project.
Illustrations. • S. unifolia (= angustifolia): Davidse & Ellis (1984). • S. unifolia (= angustifolia), TS leaf blade: Davidse & Ellis (1984). • S. unifolia (= angustifolia), epidermis of leaf blade and sheath: Davidse & Ellis (1984)
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’.