The grass genera of the world
Habit, vegetative morphology. Annual, or perennial; caespitose. Culms 10–150 cm high; herbaceous (soft, geniculate or erect); branched above, or unbranched above. Culm internodes hollow. Plants unarmed. Leaves non-auriculate. Leaf blades linear to linear-lanceolate; narrow; sometimes tapered to a setaceous point; flat; without abaxial multicellular glands; without cross venation. Ligule an unfringed membrane.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; exposed-cleistogamous, or chasmogamous (?).
Inflorescence. Inflorescence paniculate; open, or contracted; usually rigid, much longer than broad, contracted and dense or much branched; with conspicuously divaricate branchlets (when much-branched), or without conspicuously divaricate branchlets; non-digitate (the branches in pseudo-whorls on a central axis); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; not secund; pedicellate.
Female-fertile spikelets. Spikelets 1–3.5 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairless (glabrous or scabrid). Hairy callus absent. Callus short; blunt.
Glumes two; very unequal to more or less equal; shorter than the spikelets; shorter than the adjacent lemmas to long relative to the adjacent lemmas; pointed (acute), or not pointed (apically rounded); awnless; carinate; similar (membranous or sub-hyaline, ovate to lanceolate, often green). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets when present, distal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets without proximal incomplete florets.
Female-fertile florets 2–14. Lemmas acute to obtuse; similar in texture to the glumes to decidedly firmer than the glumes (translucent or thinly leathery); not becoming indurated; entire, or incised; pointed, or blunt; not deeply cleft (sometimes emarginate or somewhat erose); awnless; hairless (the nerves sometimes scabrid); often with raised nerves; 3 nerved. Palea present; relatively long; entire (apically rounded or truncate), or apically notched (3-lobed); awnless, without apical setae; thinner than the lemma to textured like the lemma; not indurated (membranous); 2-nerved; 2-keeled. Palea keels glabrous, or scabrous. Lodicules present; 2; free; fleshy; glabrous. Stamens 2. Anthers 0.2–1 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea. Hilum short. Pericarp fused. Embryo large. Endosperm containing only simple starch grains.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the intercostals much broader); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type, or panicoid-type to chloridoid-type (i.e. paicoid type, or intermediate). Microhair apical cell wall of similar thickness/rigidity to that of the basal cell to thinner than that of the basal cell and often collapsed. Microhairs in D. confertiflora, 37.5–45 microns long. Microhair basal cells 24–27 microns long. Microhairs 8.4–9 microns wide at the septum. Microhair total length/width at septum 4.2–5. Microhair apical cells 36–37.5 microns long. Microhair apical cell/total length ratio 0.45–0.52. Stomata common; 21–24 microns long. Subsidiaries dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (solitary); not silicified. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; horizontally-elongated smooth to rounded, or saddle shaped (a few), or panicoid-type.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheath outlines uneven to even. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade nodular in section to adaxially flat. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (each group with a large, deep-penetrating median cell). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries); forming figures (in the primaries). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Cytology. Chromosome base number, x = 10. Chromosomes small.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Eragrostideae; Eragrostidinae. 7 species.
Distribution, phytogeography, ecology. Americas, Australia, Asia, Africa.
Helophytic; shade species, or species of open habitats; glycophytic.
References, etc. Morphological/taxonomic: de Winter 1960; Koch (1978) argues for reduction to sectional level, on the grounds that only one character (the membranous, unfringed ligule) distinguishes Diandrochloa absolutely from Eragrostis. Leaf anatomical: studied by us - D. confertiflora (J.M. Black) de Winter.
Illustrations. • General aspect
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’.