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The grass genera of the world

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

Chloris O. Swartz

From the Greek chloros (green), referring to the leaves; alternatively, named for Chloris (The Green One), mythological Greek goddess of flowers.

Windmill Grasses.

Type species: Type: C. cruciata (L.) Sw.

Including Actinochloris Steud., Agrostomia Cerv., Apogon Steud., Chloridopsis Hack., Chloropsis Kuntze, Chlorostis Raf., Geopogon Steud., Heterolepis Boiss., Leptochloris Kuntze, Phacellaria Steud.

Excluding Daknopholis (C. boivinii), Ochthochloa, Pterochloris, Stapfochloa (= C. lamproparia)

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 10–300 cm high; herbaceous; branched above, or unbranched above. Culm nodes glabrous. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate. Sheaths usually not compressed and keeled. Leaf blades linear; narrow; flat, or folded, or rolled; without abaxial multicellular glands; without cross venation; persistent; once-folded in bud. Ligule a fringed membrane to a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; outbreeding and inbreeding; exposed-cleistogamous, or chasmogamous; with hidden cleistogenes, or without hidden cleistogenes. The hidden cleistogenes when present, subterranean. Apomictic, or reproducing sexually.

Inflorescence. Inflorescence of spicate main branches (rarely a single raceme); deciduous in its entirety, or not deciduous; digitate, or subdigitate (except C. roxburghana). Primary inflorescence branches 2–30 (pectinate or the spikelets appressed). Rachides hollowed, or flattened. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes nearly always persistent. Spikelets solitary, or paired; secund (on the dorsiventral rachis); biseriate; subsessile, or pedicellate; not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets 1.8–5.5 mm long; adaxial; compressed laterally; nearly alwyays disarticulating above the glumes (the glumes usually persistent), or falling with the glumes (rarely); not disarticulating between the florets, or disarticulating between the florets; with conventional internode spacings (or at least, without the modified internode of Oxychloris). Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus present (usually minute). Callus short; blunt.

Glumes two; very unequal (divergent); (the longer) about equalling the spikelets; long relative to the adjacent lemmas; dorsiventral to the rachis to lateral to the rachis; pointed (acute or acuminate); awnless; similar to very dissimilar (narrow, membranous, or the lower sometimes subulate). Lower glume 1 nerved. Upper glume 1–4 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets (at least one of these conspicuous - the spikelet ‘with two florets’). The distal incomplete florets 2–5; merely underdeveloped. Spikelets without proximal incomplete florets.

Female-fertile florets 1 (rarely 2). Lemmas similar in texture to the glumes to decidedly firmer than the glumes (membranous or cartilaginous); not becoming indurated; entire (truncate), or incised; when incised 2 lobed; not deeply cleft; awned. Awns 1 (usually), or 3; median, or median and lateral (rarely?); the median similar in form to the laterals (if laterals present); from a sinus, or apical; non-geniculate; entered by one vein. Lemmas hairy (at the margins, often decoratively), or hairless; carinate; without a germination flap; 1–7 nerved. Palea present; relatively long; entire to apically notched; awnless, without apical setae; not indurated (hyaline or membranous); 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 0.2–1.3 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white, or red pigmented.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; ellipsoid (to lanceolate); shallowly longitudinally grooved, or not grooved; not noticeably compressed (subterete), or trigonous. Hilum short. Pericarp free to fused. Embryo large (1/2 to 2/3 the grain length). Endosperm hard; without lipid; containing only simple starch grains, or containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting, or overlapping.

Seedling with a long mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved; 6–12 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae not over-arching the stomata; several per cell (as small finger-like projections). Long-cells similar in shape costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; usually more or less spherical; ostensibly one-celled, or clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs with ‘partitioning membranes’ (in C. gayana, also in ×Cynochloris). The ‘partitioning membranes’ in the basal cell. Microhairs 5–21 microns long. Microhair basal cells 9 microns long. Microhair total length/width at septum about 1.5. Microhair apical cells 5–18 microns long. Microhair apical cell/total length ratio about 0.5. Stomata common; about 18 microns long. Subsidiaries non-papillate; triangular (mostly), or dome-shaped (low). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; in cork/silica-cell pairs, or not paired; silicified (usually). Intercostal silica bodies imperfectly developed; tall-and-narrow, or saddle shaped. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present in alternate cell files of the costal zones; saddle shaped, or tall-and-narrow to crescentic.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; biochemical type PCK (6 species); XyMS+. PCR sheath outlines uneven. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions usually absent, or present (in C. virgata). Maximum number of extension cells in C. virgata 2. PCR cells with a suberised lamella. PCR cell chloroplasts ovoid; with well developed grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (and the colourless tissue often extended adaxially across the lamina), or not traversed by colourless columns. Leaf blade ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially, or without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups (usually, but the groups sometimes restricted to midrib hinges); in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans (these groups sometimes continuous with traversing colourless columns). Many of the smallest vascular bundles unaccompanied by sclerenchyma, or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Phytochemistry. Tissues of the culm bases with abundant starch. Leaves containing flavonoid sulphates (1 species), or without flavonoid sulphates (3 species). Leaf blade chlorophyll a:b ratio 3.23–3.93.

Cytology. Chromosome base number, x = 10. 2n = 14, 20, 26, 30, 36, 40, 72, 80, and 100. 2, 3, 4, 5, 8, and 10 ploid. Chromosomes ‘small’. Haploid nuclear DNA content 0.35 pg (1 species). Mean diploid 2c DNA value 0.7 pg (1 species). Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Eleusininae. About 55 species.

Distribution, phytogeography, ecology. Tropical and warm temperate.

Commonly adventive. Mesophytic, or xerophytic; species of open habitats. Diverse habitats, mostly in short grassland on poor soil or disturbed ground.

Economic aspects. Significant weed species: C. barbata, C. gayana, C. halophila (in North America), C. pilosa, C. polydactyla, C. pycnothrix, C. virgata. Cultivated fodder: C. gayana (Rhodes). Important native pasture species: C. roxburghiana, C. virgata.

Hybrids. Intergeneric hybrids with Cynodon - ×Cynochloris Clifford & Everist: several species involved.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia cacabata and Puccinia chloridis. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium, Sphacelotheca, and Ustilago.

References, etc. Morphological/taxonomic: Anderson 1974; Jacobs and Highet 1988. Leaf anatomical: Metcalfe 1960; studied by us - C. gayana Kunth, C. truncata R. Br.

Illustrations. • C. pectinata, pumilio, truncata, virgata: Gardner, 1952. • C. gayana Fl. W. Trop. Afr. (1936). • C. pycnothrix: Gibbs Russell et al., 1990. • Inflorescences. • Florets. • Inflorescence detail (C. truncata). • Spikelet in situ (C. truncata). Chloris truncata, showing the proximal hermaphrodite floret (stamens and stigmas detectable through the translucent lemma), and the distal incomplete one. • Disarticulated spikelet (C. virgata). • Florets (C. virgata). • Germinating C. virgata. Chloris virgata. Radicle pushing seedling out of floret. • C. truncata, abaxial epidermis of leaf blade: this project. • C. gayana, T.S. leaf blade: this project. • Pollen antigens: Watson and Knox (1976). • Microhairs of Chloris gayana: longitudinal EM sections (Amarasinghe)

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.’.