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The grass genera of the world

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

Pseudochaetochloa A. Hitchc.

From the Greek pseudos (false) and chloa (a grass), with reference to Chaetochloa (a synonym of the grass genus Setaria).

~ Pennisetum

Type species: Type: P. australiensis Hitchc.

Habit, vegetative morphology. Perennial; caespitose. Culms 50–80 cm high (female), or 50–120 cm high (male); herbaceous; branched above. Culm nodes hairy (usually), or glabrous. Culm leaf sheaths rounded. Culm internodes solid. Leaves non-auriculate. Leaf blades narrow; 20–50 cm long, 1–5.5 mm wide; without cross venation; persistent. Ligule a fringe of hairs; 0.7–2.3 mm long.

Reproductive organization. Plants dioecious; without hermaphrodite florets. The spikelets all alike in sexuality; female-only, or male-only. Plants outbreeding.

Inflorescence. Inflorescence (male and female) 8–12 cm long paniculate; contracted (the spikelets in clusters of 1–5 in males, solitary in females, with reduced-branch bristles); spicate. Primary inflorescence branches inserted all around the main axis. Inflorescence axes not ending in spikelets. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets with ‘involucres’ of ‘bristles’ (these deciduous, clustered or solitary, 3–9 mm long in the male, 15–25 mm in the female). The ‘bristles’ relatively slender, not spiny; deciduous with the spikelets. Spikelets solitary in the female, clustered in the male; not secund; sessile (female), or pedicellate (male, with pedicels 0.3–1.4 mm long). Pedicel apices discoid.

Female-sterile spikelets. The male spikelets about 4.1–7.2 mm long, not compressed, falling with the glumes. Rachilla not prolonged. Glumes 2, unequal, membranous, much shorter than the adjacent lemmas, 3-nerved. Two male florets per spikelet, the lemmas 5-nerved. Palea conventionally eu-panicoid, 2-nerved. Lodicules 2, fleshy. Rachilla of male spikelets terminated by a male floret. The male spikelets with glumes; without proximal incomplete florets; 2 floreted. The lemmas awnless. Male florets 2.

Female-fertile spikelets. Spikelets 4.5–5.9 mm long; lanceolate; compressed dorsiventrally; falling with the glumes (along with the associated bristle-branch structures). Rachilla terminated by a female-fertile floret.

Glumes two; very unequal to more or less equal; shorter than the spikelets; pointed, or not pointed; awnless (muticous or mucronate); non-carinate; membranous. Lower glume 0–3 nerved. Upper glume 3 nerved, or 5 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate to epaleate. Palea of the proximal incomplete florets much reduced. The proximal incomplete florets sterile. The proximal lemmas membranous, lanceolate; muticous or mucronate, awnless; 5 nerved; less firm than the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas lanceolate; coriaceous, decidedly firmer than the glumes; unwrinkled, striate (without grooves); entire; pointed (acute or acuminate); awnless; hairy; non-carinate. Palea present; relatively long; awnless, without apical setae; textured like the lemma (coriaceous).

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 (quite thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (72–)75–78 microns long; 6–7.5 microns wide at the septum. Microhair total length/width at septum 10.12. Microhair apical cells (37.5–)39–40.5(–42) microns long. Microhair apical cell/total length ratio 0.52–0.56. Stomata common; 36–42 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Prickles abundant. Costal short-cells conspicuously in long rows. Costal silica bodies horizontally-elongated crenate/sinuous, or ‘panicoid-type’; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines uneven. PCR sheath extensions present. Maximum number of extension cells 1. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section; with the ribs very irregular in sizes. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present, or absent; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. 1 species (P. australiensis).

Distribution, phytogeography, ecology. Australia.

Species of open habitats. Stony slopes.

Rusts and smuts. Smuts from Tilletiaceae. Tilletiaceae — Tilletia (T. pseudochaetochloae).

References, etc. Leaf anatomical: studied by us.

Special comments. Initially only male plants were described under this genus, when it was established that Pennisetum arnhemicum F. Muell. is the male component of a distinct genus. Fruit data wanting. Illustrations. • P. australiensis: Gardner, 1952. • Male inflorescence, spikelet (P. australiensis): E. Hickman. • Male spikelet details (P. australiensis): E. Hickman. • Female inflorescence and spikelets (P. australiensis): E. Hickman. • Female spikelet details (P. australiensis): E. Hickman. • P. australiensis, abaxial epidermis of leaf blade: this project

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.’.