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The grass genera of the world

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

Phacelurus Griseb.

Including Pseudophacelurus (Steud.) A. Camus

Excluding Jardinea, Pseudovossia, Thyrsia

Habit, vegetative morphology. Robust perennial. Culms 20–150 cm high; herbaceous (tough); branched above, or unbranched above. Leaf blades linear; narrow; flat, or folded, or acicular (rarely, when represented by the midrib); without cross venation. Ligule an unfringed membrane.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite (rarely), or hermaphrodite and male-only, or hermaphrodite and sterile; overtly heteromorphic (the pedicellate spikelets usually smaller or vestigial), or homomorphic; in both homogamous and heterogamous combinations, or all in heterogamous combinations.

Inflorescence. Inflorescence of spicate main branches (usually terminal, of flattened spicate ‘racemes’); usually digitate, or subdigitate (the racemes rarely solitary, or on an elongated axis); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes spicate ‘racemes’ to spikelike; clustered (on a common axis, rarely solitary); with substantial rachides; disarticulating; disarticulating at the joints. ‘Articles’ non-linear (clavate to inflated, hollowed at the apex); with a basal callus-knob; disarticulating transversely; glabrous. Spikelets paired; sessile and pedicellate (the pedicels resembling the internodes); consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis (not articulated, by contrast with Pseudovossia). The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets hermaphrodite (rarely), or male-only, or sterile.

Female-sterile spikelets. Pedicelled spikelets usually more or less resembling the sessile but usually smaller, rarely bisexual and sometimes vestigial.

Female-fertile spikelets. Spikelets compressed dorsiventrally (dorsally flat, convex or rarely concave); falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus short (minute); blunt (truncate).

Glumes two; more or less equal; long relative to the adjacent lemmas; hairless; awnless; carinate (G2), or non-carinate (G1); very dissimilar (leathery to membranous, the G1 2-keeled and flat, the G2 cymbiform). Lower glume two-keeled (sometimes winged); flattened on the back; not pitted; relatively smooth. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; male, or sterile. The proximal lemmas awnless; 2 nerved; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes (hyaline); not becoming indurated; entire; pointed, or blunt; awnless; non-carinate; without a germination flap; 3 nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Stigmas 2.

Fruit, embryo and seedling. Fruit compressed dorsiventrally. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower, more regularly rectangular); of similar wall thickness costally and intercostally. Intercostal zones with typical long-cells, or exhibiting many atypical long-cells (some of them short, in places, in P. huillensis). Mid-intercostal long-cells rectangular, or rectangular and fusiform (in P. huillensis); having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type; 57–60 microns long; 7.5–9 microns wide at the septum. Microhair total length/width at septum 6.3–7.1. Microhair apical cells 30–32 microns long. Microhair apical cell/total length ratio 0.5–0.55. Stomata common; 36–39 microns long. Subsidiaries triangular (predominantly an extreme form, in P. huillensis), or dome-shaped. Guard-cells overlapping to flush with the interstomatals (clearly overlapping them in places, in P. huillensis). Intercostal short-cells common; in cork/silica-cell pairs; silicified. Costal short-cells predominantly paired. Costal silica bodies ‘panicoid-type’; not sharp-pointed.

Transverse section of leaf blade, physiology. Leaf blades consisting of midrib (e.g. P. franksae), or ‘laminar’.

C4; XyMS–. PCR sheath outlines even. PCR sheath extensions absent. PCR cell chloroplasts centrifugal/peripheral. Leaf blade adaxially flat (or with only slight ribs, over the main bundles, in P. huillensis). Midrib very conspicuous (or the blade more or less reduced to its midrib); having a conventional arc of bundles (abaxially); with colourless mesophyll adaxially (and the colourless tissue extending laterally, about halfway to the margins, in the lamina of P. huillensis). Bulliforms not present in discrete, regular adaxial groups (the epidermis mostly more or less bulliform). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with all the primaries, in P. huillensis); forming ‘figures’ (forming ‘anchors’, in places).

Special diagnostic feature. The lower glume of the pedicellate spikelet awnless.

Cytology. Chromosome base number, x = 10. 2n = 20 and 40. 2 and 4 ploid.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae. 7 species.

Distribution, phytogeography, ecology. Africa to Indo-China and Japan.

Helophytic to mesophytic; shade species, or species of open habitats; glycophytic. Woodland and grassland, in moist places.

Rusts and smuts. Rusts — Puccinia.

References, etc. Morphological/taxonomic: Clayton 1978b. Leaf anatomical: studied by us - P. huillensis (Rendle) Stapf; photos of P. franksae provided by R.P. Ellis.

Illustrations. • P. franksae, as Ischaemum: Wood and Evans (1904), Natal Plants. • General aspect (P. franksae): 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.’.