| # The grass genera of the world |

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

### Plectrachne Henrard

From the Greek plektron (a spur or spear-point) and achne (a scale or chaff), alluding to stiff, awned lemmas or sharp callus?.

~ Triodia: cf. Lazarides in Austral. Syst. Bot. 10: 381–489 (1997)

Type species: Type: P. schinzii Henrard.

Habit, vegetative morphology. Perennial; caespitose. Culms 20–175 cm high. Culm nodes glabrous. The shoots aromatic. Leaves mostly basal; non-auriculate. Leaf blades narrow; acicular; hard, woody, needle-like, or hard, woody, needle-like to not needle-like (i.e., sometimes softer-leaved than in Triodia s. str.); without abaxial multicellular glands; without cross venation; persistent. Ligule a fringe of hairs (usually very short).

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

Inflorescence. Inflorescence paniculate; open, or contracted; when contracted spicate; non-digitate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets compressed laterally; disarticulating above the glumes; with conventional internode spacings (by contrast with Symplectrodia). Rachilla prolonged beyond the uppermost female-fertile floret; hairy; the rachilla extension with incomplete florets. Hairy callus present.

Glumes two; more or less equal; about equalling the spikelets to exceeding the spikelets; long relative to the adjacent lemmas; awnless; carinate, or non-carinate. Lower glume 3–7 nerved. Upper glume 3–7 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets.

Female-fertile florets 3–10. Lemmas becoming indurated to not becoming indurated (leathery to indurated); incised; 3 lobed; deeply cleft (the lobes longer than the body of the lemma); awned. Awns 1, or 3; median, or median and lateral (the lobes awnlike); the median similar in form to the laterals (when laterals present); from a sinus; non-geniculate; entered by one vein. The lateral awns shorter than the median. Lemmas hairy, or hairless; non-carinate; 9 nerved. Palea present; relatively long; 2-nerved. Lodicules present; 2; free; fleshy; glabrous; heavily vascularized. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit small; ellipsoid. Hilum short. Pericarp fused.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous and lacking (centre of leaf/margins). Papillae absent (but abundant adaxially). Microhairs present (? - probably, but well hidden in the grooves); (adaxial) elongated; clearly two-celled; chloridoid-type (where seen, adaxially). Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhair basal cells 21 microns long. Stomata absent or very rare (or if present, hidden in the narrow grooves). Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed to absent; ‘panicoid-type’; not sharp-pointed.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section infolded permanently; circular. The adaxial channel parallel-sided, with a digitate base.

C4. The anatomical organization unconventional. Organization of PCR tissue Triodia type. XyMS+. PCR sheath outlines even. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (these linking the adaxial and abaxial grooves, at least in the middle part of the blade where the PCR cells do not ‘drape’); with arm cells. Leaf blade ‘nodular’ in section, or with distinct, prominent adaxial ribs and ‘nodular’ in section (the abaxial grooves sometimes lacking towards the leaf margins); with the ribs very irregular in sizes. Midrib conspicuous (by its position); with one bundle only; without colourless mesophyll adaxially (but the blade often with blocks of abaxial colourless tissue towards the margins). Bulliforms present in discrete, regular adaxial groups (as part of the traversing columns), or not present in discrete, regular adaxial groups (bulliforms often not recognisable as such); if recognisable, associated with colourless mesophyll cells to form deeply-penetrating fans (incorporated in the traversing columns of colourless cells). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present, or absent; forming ‘figures’. Sclerenchyma all associated with vascular bundles, or not all bundle-associated (sometimes with a continuous abaxial layer). The ‘extra’ sclerenchyma when present, in abaxial groups, or in a continuous abaxial layer.

Classification. Watson & Dallwitz (1994): Chloridoideae; Triodieae. Soreng et al. (2015): Chloridoideae; Cynodonteae; Triodiinae. 16 species.

Distribution, phytogeography, ecology. Australia.

Xerophytic (but less so than Triodia s. stricto); species of open habitats. Sandy or stony, arid soils.

References, etc. Morphological/taxonomic: Jacobs 1971. Leaf anatomical: Metcalfe 1960; studied by us - P. melvillei C.E. Hubb., P. schinzii Henrard.

Illustrations. • General morphology (Plectrachne pungens): Jacobs, 1971. • Spikelets of Plectrachne pungens. • Spikelet of Plectrachne helmsii. • Floret of Plectrachne helmsii. • Glumes of Plectrachne uniaristata. • Glume tip of Plectrachne uniaristata. • Plectrachne schinzii, 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: 15th June 2025. delta-intkey.com’.

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