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The grass genera of the world

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

Pogonarthria Stapf

From the Greek pogon (beard) and arthron (joint), presumably referring to hairy rachilla joints.

Habit, vegetative morphology. Annual, or perennial; caespitose. Culms 13–250 cm high; herbaceous; branched above, or unbranched above. Culm nodes glabrous. Culm internodes solid. Plants unarmed. Young shoots intravaginal. Leaves mostly basal, or not basally aggregated; non-auriculate; without auricular setae (but the mouth of the sheath sometimes hairy). Leaf blades linear; narrow; 2–5 mm wide; setaceous, or not setaceous; flat, or rolled (convolute); without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane, or a fringe of hairs; 0.25–0.5 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence of spicate main branches (a raceme of numerous, up-curved, spike-like branches); with conspicuously divaricate branchlets, or without conspicuously divaricate branchlets (when immature); non-digitate (the branches tending to whorls). Rachides the slender spikelet bearing rachides flattened and sinuous. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes spikelike. The racemes without spikelets towards the base. Spikelet-bearing axes disarticulating; falling entire (the racemes falling after the spikelets have broken up). Spikelets solitary; secund (the spikelet bearing rachides one-sided); biseriate; shortly pedicellate; imbricate.

Female-fertile spikelets. Spikelets 3.3–7.8 mm long; compressed laterally; disarticulating above the glumes; not disarticulating between the florets, or disarticulating between the florets (disarticulating between the lemmas, or the glumes and lemmas falling irregularly to leave the paleas on the persistent rachilla); with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairy (ciliate at the disarticulating apices); the rachilla extension with incomplete florets. Hairy callus absent. Callus absent.

Glumes two; very unequal (G1 about 2/3 of G2); shorter than the spikelets; shorter than the adjacent lemmas; lateral to the rachis; hairless; glabrous (scabrid on the keel); pointed (subacuminate); awnless; carinate; similar (rigidly membranous). Lower glume shorter than the lowest lemma; 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped; awnless. Spikelets without proximal incomplete florets.

Female-fertile florets 2–8 (decreasing in size upwards). Lemmas acute to acuminate; similar in texture to the glumes; not becoming indurated; entire; pointed; awnless (but sometimes subaristate); hairless; glabrous (scabrid on the median nerve); more or less carinate; without a germination flap; 3 nerved; with the nerves non-confluent. Palea present; relatively long; minutely apically notched; awnless, without apical setae; textured like the lemma (membranous); not indurated; 2-nerved; 2-keeled. Palea keels wingless; scabrous. Lodicules present; 2; free; fleshy (but narrow); glabrous; not or scarcely vascularized. Stamens 3. Anthers 0.6–1.3 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; brown.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (0.5–1 mm long); ellipsoid; obtusely trigonous. Hilum short. Pericarp fused. Embryo large (about 1/2 grain length).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally, or markedly different in shape costally and intercostally (the costals smaller); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls (deeply, and pitted). Microhairs present, or absent (from some material of P. squarrosa); more or less spherical to elongated; clearly two-celled; when present, chloridoid-type (rather variable in shape, cf. Eragrostis). Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs without ‘partitioning membranes’ (in P. squarrosa); (27–)28.5–30 microns long (P. fleckii), or 36–54 microns long (P. squarrosa). Microhair basal cells 21–24 microns long. Microhairs 11.4–15 microns wide at the septum (P. fleckii). Microhair total length/width at septum 1.9–2.5 (P. fleckii). Microhair apical cells (5.4–)6–7.5 microns long (P. fleckii), or 14–22 microns long (P. squarrosa). Microhair apical cell/total length ratio 0.2–0.28 (P. fleckii), or 0.43 (P. squarrosa). Stomata common; (22.5–)25.5–28.5(–30) microns long. Subsidiaries triangular (a few), or dome-shaped (mostly). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies absent, or imperfectly developed; rounded, or crescentic, or saddle shaped. Costal short-cells conspicuously in long rows (P. fleckii), or predominantly paired and neither distinctly grouped into long rows nor predominantly paired (over different veins). Costal silica bodies present in alternate cell files of the costal zones; saddle shaped to crescentic (P. squarrosa), or ‘panicoid-type’ (P. fleckii); not sharp-pointed.

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

C4; XyMS+. PCR sheath outlines uneven to even (more even in P. fleckii than in P. squarrosa). PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions present, or absent. Maximum number of extension cells when present, 1. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells, or not traversed by colourless columns. Leaf blade ‘nodular’ in section to adaxially flat (the ribs very low). Midrib conspicuous (bundle somewhat larger), or not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (a few, with large median cells), or associated with colourless mesophyll cells to form deeply-penetrating fans (often linked to the abaxial epidermis by girders of colourless cells). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (nearly all the bundles); forming ‘figures’ (all I’s or anchors). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Cytology. 2n = 40, or 42.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Eragrostideae; Eragrostidinae. 4 species.

Distribution, phytogeography, ecology. Tropical and southern Africa.

Mesophytic to xerophytic; species of open habitats; glycophytic. Savanna grasslands, often in shallow or sandy soils or in disturbed places.

Economic aspects. Significant weed species: P. squarrosa.

Rusts and smuts. Rusts — Puccinia.

References, etc. Morphological/taxonomic: Rendle 1899. Leaf anatomical: Metcalfe 1960; this project; photos of P. fleckii and P. squarrosa provided by R.P. Ellis.

Illustrations. • P. squarrosa, as P. falcata: Hook. Ic. Pl. 27 (1901). • General aspect (P. squarrosa): Gibbs Russell et al., 1990. • P. squarrosa, abaxial epidermis of leaf blade: this project. • P. squarrosa, abaxial epidermis of leaf blade: this project. • P. squarrosa, abaxial leaf blade epidermal detail: this project


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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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