The grass genera of the world
Habit, vegetative morphology. Perennial; rhizomatous and stoloniferous (mat-forming, with long decumbent stems). Culms 4–45 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes hollow. Plants unarmed. Young shoots intravaginal. Leaves mostly basal (the culm leaves reduced); non-auriculate. Leaf blades linear to linear-lanceolate; narrow; 1.5–2.5 mm wide (and 1–18 cm long); flat; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane (minutely fimbriate); truncate; to 0.4 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches (of appressed racemes, 2–3 cm long); contracted; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes racemes. The racemes without spikelets towards the base. Spikelet-bearing axes persistent. Spikelets solitary; secund (on the racemes, at maturity deflexed upwards from the G1, which remains erect against the rachis); pedicellate; imbricate.
Female-fertile spikelets. Spikelets 3.5–4.5 mm long; adaxial; compressed dorsiventrally; planoconvex; disarticulating above the glumes; with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus present (small, the hairs short). Callus short; blunt.
Glumes two; very unequal; (the upper) long relative to the adjacent lemmas; dorsiventral to the rachis; hairless; glabrous; pointed (G2), or not pointed (G1); awnless; non-carinate (G2 may be slightly keeled towards apex); very dissimilar (G1 hyaline-membranous, nerveless, obtuse, G2 lanceolate, firmly membranous, 1 nerved). Lower glume 0.5 times the length of the upper glume; shorter than the lowest lemma; 0 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only.
Female-fertile florets 1. Lemmas similar in texture to the glumes (like the G2); not becoming indurated; entire; pointed, or blunt; shortly mucronate; hairy (on the lateral nerves, below), or hairless; non-carinate; having the margins inrolled against the palea; without a germination flap; 3 nerved; with the nerves confluent towards the tip. Palea present; relatively long (narrowly elliptic, nearly equalling the lemma); tightly clasped by the lemma; entire (truncate), or apically notched; awnless, without apical setae; thinner than the lemma; not indurated (subhyaline); 2-nerved; 2-keeled. Palea keels wingless; glabrous. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 2 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical to elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 27.6–33 microns long. Microhair basal cells 18–21 microns long. Microhairs 11.4–15 microns wide at the septum. Microhair total length/width at septum 2.6. Microhair apical cells 10.5–12.9 microns long. Microhair apical cell/total length ratio 0.4. Stomata common. Subsidiaries dome-shaped and triangular (mostly dome-shaped). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies present and perfectly developed; tall-and-narrow, crescentic, and saddle shaped. Costal short-cells conspicuously in long rows (in places), or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present in alternate cell files of the costal zones; predominantly saddle shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma; without adaxial palisade; traversed by columns of colourless mesophyll cells (in places), or not traversed by colourless columns. Leaf blade adaxially flat. Midrib conspicuous (by virtue of its wide, rounded abaxial keel, contrasting with the flattened keels of the other main bundles); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these sometimes linked with traversing colourless columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (most bundles with Is or anchors). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Traginae. 1 species (P. rigida).
Distribution, phytogeography, ecology. South Africa.
Mesophytic; species of open habitats; glycophytic. Mountain grassland.
References, etc. Morphological/taxonomic: de Winter 1966b. Leaf anatomical: studied by us.
Special comments. Fruit data wanting. Illustrations. • General aspect (P. rigida): Gibbs Russell et al., 1990
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’.