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The grass genera of the world

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

Parectenium P. Beauv. corr. Stapf

From the Greek para (resembling) and ktenion (a little comb), alluding to comblike racemes.

~ Plagiosetum

Type species: Type: P. novae-hollandiae P.Beauv.

Including Paractaenium P. Beauv.

Habit, vegetative morphology. Annual; caespitose. Culms 30–90 cm high; herbaceous; branched above. Culm nodes glabrous. Culm leaf sheaths keeled, or compressed. Culm internodes solid. Leaves non-auriculate. Leaf blades narrow; 2–5 mm wide; flat; without cross venation; persistent. Ligule a fringed membrane; short.

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

Inflorescence. Inflorescence of spicate main branches (with up to 5 spikelets per raceme, but reducing to one or two); the racemes finally deflexing; non-digitate. Primary inflorescence branches borne distichously, or inserted all around the main axis. Inflorescence axes not ending in spikelets (each short lateral raceme ending in a bristle). Rachides hollowed. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced, or spikelike; disarticulating (but the main axis persistent); falling entire (the short branches articulated at their bases, falling whole). Spikelets subtended by solitary ‘bristles’ (individually, at least at the base of the racemelets, by contrast with Plagiosetum). The ‘bristles’ deciduous with the spikelets. Spikelets solitary; secund; shortly pedicellate. Pedicel apices truncate.

Female-fertile spikelets. Spikelets 3.5–5 mm long; oblong, or elliptic, or lanceolate, or ovate, or obovate; abaxial; compressed dorsiventrally; falling with the glumes (and with the branch). Rachilla terminated by a female-fertile floret.

Glumes two; relatively large; very unequal; (the G2, which equals the spikelet) long relative to the adjacent lemmas; dorsiventral to the rachis; not pointed; awnless; non-carinate. Lower glume 3–5 nerved. Upper glume 9–13 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets reduced. The proximal incomplete florets sterile. The proximal lemmas awnless; 9–11 nerved; decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas (herbaceous-membranous, similar to the G2); not becoming indurated.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes (leathery or cartilaginous); rugose; becoming indurated (slightly); yellow in fruit, or brown in fruit; entire; pointed, or blunt; awnless; hairless (shortly ciliolate at the apex); non-carinate; having the margins lying flat on the palea; 3–5 nerved. Palea present; relatively long (elliptical); entire; awnless, without apical setae; textured like the lemma; slightly indurated (like the lemma). Lodicules present; 2; fleshy. Stamens 3. Anthers about 2 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit small; compressed dorsiventrally. Hilum short. Embryo small. Endosperm containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells having markedly sinuous walls. Microhairs present; panicoid-type; (36–)47–50(–63) microns long; 5.4–7.5 microns wide at the septum. Microhair total length/width at septum 7.5–10.5. Microhair apical cells (22.5–)28.5–42(–43.5) microns long. Microhair apical cell/total length ratio 0.59–0.7. Stomata common; 21–25.5 microns long. Subsidiaries dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies ‘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. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma. 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 not present in discrete, regular adaxial groups (the epidermis extensively bulliform). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. 1–2 species (P. novae-hollandiae, P. refractum).

Distribution, phytogeography, ecology. Australia.

Species of open habitats; halophytic, or glycophytic. Sandy places, sometimes maritime.

References, etc. Leaf anatomical: studied by us - P. novae-hollandiae Beauv.

Illustrations. • P. novae-hollandiae: Gardner, 1952. • P. novae-hollandiae: P. Beauv. (1812)

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.’.