The grass genera of the world
Type species: Type: P. rigidum Desv. = P. dentatum.
Including Chondrolaena Nees, Prionachne Nees
Habit, vegetative morphology. Slender annual; caespitose. The flowering culms leafless. Culms 4–43 cm high; herbaceous; branched above, or unbranched above. Culm nodes glabrous. Culm internodes hollow. Plants unarmed; with multicellular glands (stalked or sessile, on the glumes of all three species, not on the leaves). Young shoots intravaginal. Leaves not basally aggregated; non-auriculate; without auricular setae (but with a tuft of hairs at the mouth of the sheath). Leaf blades linear (or filiform); narrow; 0.5–2(–3) mm wide (less than 8 cm long); flat, or rolled; without cross venation; persistent. Ligule a fringed membrane to a fringe of hairs; 0.3–1.5 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence a single spike, or a single raceme (spike-like); contracted (3–8 cm long, the axis curved beside each spikelet); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary, or paired; secund; biseriate; sessile to subsessile; consistently in long-and-short combinations, or not in distinct long-and-short combinations.
Female-fertile spikelets. Spikelets 3–7 mm long; adaxial (the upper glume gaping widely at anthesis); compressed laterally; disarticulating above the glumes; disarticulating between the florets (but the disarticulated florets remaining for some time within the persistent glumes). Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension naked.
Glumes two; more or less equal (the lower slightly longer); about equalling the spikelets; long relative to the adjacent lemmas (exceeding them); dorsiventral to the rachis (in P. pholiuroides), or lateral to the rachis; hairy, or hairless (keels and sometimes the nerves tuberculate or pectinate); not pointed (rounded); awnless; carinate (strongly, often asymmetrically); similar (navicular, rigid, leathery with membranous margins enfolding the floret, usually with multicellular glands). Lower glume about equalling the lowest lemma, or much exceeding the lowest lemma; 5–8 nerved. Upper glume 5–8 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped; awnless.
Female-fertile florets 2. Lemmas acute, lanceolate or lanceolate-oblong; less firm than the glumes; not becoming indurated (thinly membranous); entire; pointed; awnless, or mucronate; hairy, or hairless. The hairs not in tufts (when present, evenly distributed). Lemmas non-carinate (abaxially rounded); without a germination flap; 3–5 nerved. Palea present (sub-linear); relatively long; apically notched; awnless, without apical setae; textured like the lemma; not indurated (hyaline, with thickened keels); 2-nerved; 2-keeled. Lodicules present (minute); 2; free; fleshy; glabrous. Stamens 3. Anthers 1.8–3.9 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit narrowly lanceolate in outline; longitudinally grooved. Hilum long-linear. Embryo small. Endosperm containing only simple starch grains.
Ovule, embryology. Micropyle not noticeably oblique. Outer integument covering no more than the chalazal half of the ovule; two cells thick at the micropylar margin. Inner integument discontinuous distally; not thickened around the micropyle. Synergids not haustorial; without large, globular starch grains.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular and fusiform; having markedly sinuous walls. Microhairs present; panicoid-type; (63–)69–75(–81) microns long; 7.5–8.4–10.5 microns wide at the septum. Microhair total length/width at septum 6.9–10. Microhair apical cells 28.5–31.5 microns long. Microhair apical cell/total length ratio 0.38–0.46. Stomata common; 31.5–36 microns long. Subsidiaries parallel-sided to dome-shaped (mostly domes-shaped). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (and solitary); silicified. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; dumb-bell shaped and nodular; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (small abaxial girders only, but with a wide adaxial strand at the top of each rib). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 7. 2n = 14. 2 ploid (all three species).
Classification. Watson & Dallwitz (1994): Arundinoideae; Danthonieae. Soreng et al. (2015): Danthonioideae; Danthonieae. 3 species.
Distribution, phytogeography, ecology. South Africa.
Helophytic (in seasonally wet places); species of open habitats; glycophytic.
References, etc. Morphological/taxonomic: Davidse, G. (1988). Bothalia 18, 143–153. Leaf anatomical: this project.
Illustrations. • General aspect (P. pholiuroides): 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: 13th November 2017. delta-intkey.com/grass’.