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The grass genera of the world

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

Sporobolus R.Br.

From the Greek spora (seed) and ballein (to throw), alluding to the free seed and (presumably) the sometimes forcible manner of its release.

Type species: Type: S. indicus (L.) R.Br.

Including Agrosticula Raddi, Bauchea Fourn., Cryptostachys Steud., Diachyrium Griseb., Spermachiton Llanos, Triachyrum A. Br.

Excluding Calamovilfa, Crypsis, Spartina(!), Thellungia

Habit, vegetative morphology. Annual (rarely), or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 5–160(–300) cm high; herbaceous; sparsely branched above, or unbranched above (usually). Culm nodes glabrous. Culm internodes solid (usually), or hollow (rarely). Plants with multicellular glands (rarely, e.g. on the pedicels in S. heterolepis), or without multicellular glands. Leaves non-auriculate. Sheath margins free. Leaf blades linear; narrow; setaceous, or not setaceous; flat, or folded, or rolled, or acicular (rarely solid-cylindrical); without abaxial multicellular glands; not pseudopetiolate; without cross venation; persistent; rolled in bud. Ligule a fringed membrane (narrow), or a fringe of hairs. Contra-ligule present (of hairs), or absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; inbreeding; exposed-cleistogamous, or chasmogamous.

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (rarely), or a single raceme (rarely), or paniculate; open to contracted (rarely with the lowest branches sterile - S. panicoides); spicate, or more or less irregular; with capillary branchlets, or without capillary branchlets. Inflorescence with axes ending in spikelets. Rachides hollowed, or flattened, or winged, or neither flattened nor hollowed, not winged. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets secund, or not secund; subsessile, or pedicellate.

Female-fertile spikelets. Spikelets 0.8–3.5(–6) mm long (i.e. usually small, but rarely to 6 mm); often fusiform; compressed laterally to not noticeably compressed; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret (rarely, Section Chaetorachis), or terminated by a female-fertile floret; the rachilla extension when present, with incomplete florets, or naked. Hairy callus absent. Callus absent, or short; (when present) blunt.

Glumes two; very unequal (G1 often very short), or more or less equal; shorter than the adjacent lemmas, or long relative to the adjacent lemmas; hairless; glabrous; awnless (occasionally mucronate); carinate (slightly), or non-carinate (convex); very dissimilar to similar (persistent or subpersistent, thinly membranous or hyaline, the upper usually resembling the lemma). Lower glume 0–2 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets (rarely). The incomplete florets when present, distal to the female-fertile florets. Spikelets without proximal incomplete florets.

Female-fertile florets 1 (species with two or more florets being rather arbitrarily excluded - cf. Eragrostis, Thellungia). Lemmas usually similar to G2; usually thinly membranous, rarely papery; not becoming indurated; entire; pointed, or blunt; awnless (S. molleri subulate-tipped); hairless; glabrous (usually shiny, often olive or grey); carinate to non-carinate; 1(–3) nerved. Palea present; relatively long; entire (seemingly in all species, when young), or apically notched to deeply bifid (often splitting as the grain develops); textured like the lemma (delicate); not indurated; 2-nerved; 2-keeled (but the back often induplicate, bringing them into contiguity). Lodicules present, or absent; when present, 2; free; fleshy; glabrous. Stamens (1–)2–3. Anthers 0.2–2.5 mm long; not penicillate. Ovary apically glabrous; without a conspicuous apical appendage. Styles free to their bases. Stigmas 2; white, or brown.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (0.3–2 mm long); compressed laterally, or compressed dorsiventrally, or not noticeably compressed (variously globular or compressed). Hilum short. Pericarp free (commonly swelling and mucilaginous when wet, forcibly ejecting the seed). Embryo large; not waisted. Endosperm hard; without lipid; containing only simple starch grains (e.g. S. cryptandrus), or containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Seedling with a long mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad (rarely), or narrow; erect; 3–5 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. 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; usually more or less spherical; ostensibly one-celled (usually), or clearly two-celled (e.g. S. wrightii); chloridoid-type. Microhair apical cell wall thinner than that of the basal cell but not tending to collapse. Microhairs with ‘partitioning membranes’. The ‘partitioning membranes’ in the basal cell. Microhairs 9–20 microns long, or 30–37 microns long (S. wrightii). Microhair basal cells 24 microns long. Microhair total length/width at septum 2. Microhair apical cell/total length ratio 0.4–0.5. Stomata common; 24–30 microns long. Subsidiaries low dome-shaped, or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired; silicified (when paired), or not silicified. Intercostal silica bodies present and perfectly developed; crescentic, or rounded, or saddle shaped, or tall-and-narrow. Costal short-cells conspicuously in long rows, or predominantly paired. Costal silica bodies present in alternate cell files of the costal zones; rounded, or saddle shaped, or tall-and-narrow, or crescentic; not sharp-pointed.

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

C4; biochemical type PCK (6 species), or NAD–ME (4 species); XyMS+. PCR sheath outlines uneven, or even. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions present, or absent. Maximum number of extension cells when present, 2–5. PCR cells with a suberised lamella. PCR cell chloroplasts ovoid, or elongated; with well developed grana; centrifugal/peripheral, or centripetal. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib conspicuous, or not readily distinguishable; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially (usually), or without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (usually), or in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans (sometimes), or combining with colourless mesophyll cells to form narrow groups penetrating into the mesophyll (e.g. S. wrightii). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Culm anatomy. Culm internode bundles in one or two rings, or in three or more rings, or scattered.

Phytochemistry. Tissues of the culm bases with abundant starch. Leaves without flavonoid sulphates (4 species). Leaf blade chlorophyll a:b ratio 3.28–3.69 (PCK), or 3.75–3.89 (NAD-ME).

Cytology. Chromosome base number, x = 9 and 10. 2n = 18, 24, 36, 38, 54, 72, 80, 88, 90, 108, and 126. 2, 4, 6, 8, 9, 10, 12, and 13 ploid. Chromosomes ‘small’. Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Zoysieae; Sporobolinae. C. 160 species.

Distribution, phytogeography, ecology. Tropical and warm temperate.

Commonly adventive. Mesophytic, or xerophytic; halophytic, or glycophytic. In diverse habitats, including coastal sand dunes.

Economic aspects. Significant weed species: S. airoides, S. africanus, S. cryptandrus, S. diander, S. elongatus, S. fertilis, S. indicus, S. neglectus, S. poiretii, S. pyramidalis, S. tremulus, S. vaginiflorus, S. virginicus, etc. Important native pasture species: S. airoides, S. cryptandrus, S. elongatus, S. helvolus, S. interruptus, S. ioclados, S. pyramidalis (in arid places), S. wrightii.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia schedonnardi. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Entyloma, Melanotaenium, and Tilletia. Ustilaginaceae — Sorosporium, Sphacelotheca, Tolyposporella, and Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; this project.

Special comments. Fairly arbitrarily but mostly readily separable from Eragrostis; see also Thellungia. Illustrations. • S. australasicus, S. actinocladus, S. capensis, S. mitchellii, S. virginicus: Gardner, 1952. • General aspect (S. africanus): Gibbs Russell et al., 1990. • General aspect (S. nitens): Gibbs Russell et al., 1990. • General aspect, spikelets (S. subtilis): Gibbs Russell et al., 1990. • Part of inflorescence, detail (S. elongatus). • Fruiting inflorescence detail (S. elongatus). • Inflorescence detail (S. indicus). • Spikelets of S. australiensis. • Opened spikelet of S. elongatus. • Opened spikelet of S. indicus. • Seedling of S. elongatus. • S. elongatus, abaxial epidermis of leaf blade: this project. • S. elongatus, TS of leaf blade: this project. • S. caroli, ultra-thin T.S. of leaf blade: this project. Sporobolus caroli. Centripetal chloroplasts in the PCR sheath cells. • S fimbriatus, leaf blade T.S. with immunofluorescent-labelled Rubisco: Hattersley, Watson and Osmond (1977). Sporobolus fimbriatus. Fluorescent-labelled Rubisco in the PCR sheath. • Microhairs of S. elongatus and Dactyoctenium aegyptium: longitudinal EM sections (Amarasinghe)


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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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