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The grass genera of the world

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

Psammagrostis C.A. Gardner & C.E. Hubb.

From the Greek psammos (sand) and agrostis (a kind of grass).

Type species: Type: P. wiseana C.A.Gardner & C.E.Hubb.

Habit, vegetative morphology. Annual; decumbent (to geniculate ascending). Plants to 50 cm in diameter. Culms 10–20 cm long; herbaceous; branched above (and below, with all the branch systems producing inflorescences). Culm nodes glabrous. Leaves not basally aggregated; non-auriculate. The sheaths inflated, constricted at the throat, striate. Leaf blades not all greatly reduced (but becoming reduced acropetally on the culms); linear-lanceolate to lanceolate (but tightly rolling when dry); narrow; 1–4 mm wide; setaceous (when dry), or not setaceous; flat, or rolled; exhibiting multicellular glands abaxially (at the base of macrohairs). The abaxial leaf blade glands intercostal. Leaf blades without cross venation; disarticulating from the sheaths; rolled in bud. Ligule a fringe of hairs. Contra-ligule absent.

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

Inflorescence. Inflorescence falsely paniculate (towards the culm tips, by proliferation of the axillary fascicles which occur in simpler form with the lower leaves); spatheate (each of the ultimate fascicles associated with a spatheole, within the axillant sheath); a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes very much reduced (each to a deciduous, slightly clavate, 3–10 mm peduncle, with a terminal spikelet and often with one or two sessile, subsessile or more or less pedicellate lateral spikelets); clustered (2–4 per axil); disarticulating; falling entire (the striated peduncles disarticulating at the base). Spikelets not secund; sessile, subsessile, and pedicellate.

Female-fertile spikelets. Spikelets 4–8 mm long; somewhat compressed laterally; falling with the glumes (and with their companions on the peduncle); not disarticulating between the florets; with distinctly elongated rachilla internodes between the florets (up to 2 mm long, clavate). Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Callus absent.

Glumes two; very unequal; shorter than the spikelets; shorter than the adjacent lemmas; lateral to the rachis (in so far as the orientation is ascertainable); hairless; slightly scabrous; not pointed (blunt or erose); awnless; carinate; very dissimilar to similar (the lower being flimsier, sometimes hyaline throughout). Lower glume 0 nerved, or 1 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped; awnless.

Female-fertile florets 3–7. Lemmas elliptical to broadly ovate; decidedly firmer than the glumes (leathery or cartilaginous, with hyaline margins); not becoming indurated; entire to incised (obtuse, truncate or slightly emarginate); not deeply cleft; mucronate; hairless; scabrous; carinate; without a germination flap; 3 nerved; with the nerves non-confluent. Palea present; relatively long; tightly clasped by the lemma; entire (the hyaline apex rounded); awnless, without apical setae; textured like the lemma (leathery to cartilaginous between the keels); 2-nerved; 2-keeled. Palea keels wingless; scabrous. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases.

Fruit, embryo and seedling. Fruit small; trigonous; sculptured. Hilum short. Pericarp free. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals relatively longer and narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; very elongated; clearly two-celled; chloridoid-type to Enneapogon-type (the slender basal cell long, relatively thick-walled, the short, rounded apical cell quite thin-walled). Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs (117–)126.6(–141) microns long. Microhair basal cells 111 microns long. Microhairs (12–)12.6(–14.4) microns wide at the septum. Microhair total length/width at septum (8.1–)10.1(–11.75). Microhair apical cells 16.5–20.7–24 microns long. Microhair apical cell/total length ratio 0.14–0.16–0.19. Stomata common; (27–)28.5(–30) microns long. Subsidiaries dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare (only one or two seen); not paired (the few seen solitary). Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; rather consistently ‘smoothed out’ dumb-bell 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 (seemingly, judging from the poor material seen). Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib not readily distinguishable; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; in simple fans (the median fan cells deeply penetrating). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (all the major bundles with small girders top and bottom). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Eragrostideae; Eragrostidinae. 1 species (P. wiseana).

Distribution, phytogeography, ecology. Australia.

Xerophytic; species of open habitats. Sandhills.

References, etc. Morphological/taxonomic: Gardner and Hubbard 1938. Leaf anatomical: studied by us.

Illustrations. • P. wiseana: Gardner, 1952. • Spikelet of P. wiseana. • Spikelet details (P. wiseana)

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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: 11th December 2017.’.