| # The grass genera of the world |

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

### Plinthanthesis Steud.

From the Greek plinthos (plinth) and anthos (flower), referring to the raceme-like inflorescence.

Wallaby grasses.

~ Rytidosperma, Danthonia sensu lato

Type species: Lecto: P. urvillei Steud.

Including Blakeochloa Veldkamp

Habit, vegetative morphology. Perennial; caespitose. Culms 20–70 cm high; herbaceous; unbranched above. Culm nodes glabrous. Leaves non-auriculate. Leaf blades narrow; setaceous to not setaceous; flat, or rolled; not pseudopetiolate; without cross venation; persistent; once-folded in bud. Ligule a fringe of hairs (short).

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

Inflorescence. Inflorescence few spikeleted to many spikeleted; paniculate; open, or contracted; with capillary branchlets to without capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 5–9 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets (the disarticulation horizontal, leading to a short, obtuse callus); with distinctly elongated rachilla internodes between the florets (the internode more than half the lemma length). Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus absent. Callus short; blunt.

Glumes two; more or less equal; shorter than the spikelets to exceeding the spikelets; long relative to the adjacent lemmas (exceeding them); hairless; glabrous, or scabrous; pointed (acute); awnless; keeled above; similar (translucent or firm). Lower glume 1 nerved, or 3 nerved. Upper glume 1 nerved, or 3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.

Female-fertile florets 2–4. Lemmas similar in texture to the glumes to decidedly firmer than the glumes (firmly membranous to leathery); not becoming indurated; incised; 2 lobed; deeply cleft (to about halfway), or not deeply cleft (the lobes minute, or up to 4 mm long); awnless, or mucronate, or awned (shortly). Awns when present, 1; median; when present, from a sinus; non-geniculate (flat, curved), or geniculate; when present, much shorter than the body of the lemma to about as long as the body of the lemma. Lemmas evenly hairy (at least below). The hairs not in tufts; not in transverse rows. Lemmas non-carinate (rounded on the back); without a germination flap; 7 nerved, or 9 nerved. Palea present; relatively long (equalling the lemma); entire to apically notched; awnless, without apical setae (densely white-hairy below); thinner than the lemma to textured like the lemma; not indurated; 2-nerved; 2-keeled. Palea keels wingless. Lodicules present; 2; membranous; glabrous; not toothed. Stamens 3. Anthers 1.5–3 mm long. Ovary apically glabrous. Styles free to their bases; free. Style bases widely separated. Stigmas 2.

Fruit, embryo and seedling. Disseminule a caryopsis enclosed in but free of the lemma and palea. Fruit free from both lemma and palea; small; golden-brown; obovate; longitudinally grooved; compressed dorsiventrally; glabrous; smooth. Hilum short, or long-linear (?). Embryo large; waisted. Endosperm hard.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (in P. paradoxa the intercostals less regular). Mid-intercostal long-cells rectangular (P. rodwayi), or rectangular to fusiform (P. paradoxa); having markedly sinuous walls. Microhairs present; panicoid-type (conventional in P. rodwayi, in P. paradoxa the basal cell fat, the apical cell conical); (54–)60–72(–81) microns long (P. paradoxa), or 60–69 microns long (P. rodwayi); 18–21–25.5 microns wide at the septum (P. paradoxa), or 11.4–12 microns wide at the septum (P. rodwayi). Microhair total length/width at septum 2.5–4 (P. paradoxa), or 5.3–6.1 (P. rodwayi). Microhair apical cells (22.5–)30–37.5(–46.5) microns long (P. paradoxa), or (17.4–)22.5–24(–28.5) microns long (P. rodwayi). Microhair apical cell/total length ratio 0.42–0.57 (P. paradoxa), or 0.26–0.41 (P. rodwayi). Stomata absent or very rare (P. rodwayi), or common (P. paradoxa, in places); in P. paradoxa (36–)45–48(–51) microns long. Subsidiaries of P. paradoxa dome-shaped, or parallel-sided (more or less). Guard-cells overlapping to flush with the interstomatals (in P. paradoxa, in which many stomata are accompanied at one end by a third ‘subsidiary’, in the form of a very short intercostal cell - a most unusual feature). Intercostal short-cells common; in cork/silica-cell pairs (and solitary); silicified. Costal short-cells conspicuously in long rows (very regular). Costal silica bodies ‘panicoid-type’; very regular cross shaped and butterfly shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs (P. rodwayi), or ‘nodular’ in section (P. paradoxa); with the ribs very irregular in sizes. Midrib not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (or at least, only inconspicuously grouped). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries - the smaller bundles often with strands only); forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Arundinoideae; Danthonieae. Soreng et al. (2015): Danthonioideae; Danthonieae. 3 species.

Distribution, phytogeography, ecology. Southeastern Australia.

Mesophytic to xerophytic; species of open habitats; glycophytic. Upland heaths.

References, etc. Morphological/taxonomic: Blake 1972a, Vickery 1956. Leaf anatomical: studied by us - P. paradoxa (R. Br.) S. T. Blake, P. rodwayi (C. E. Hubbard) S. T. Blake.

Illustrations. • Plinthanthesis paradoxa: Linder et al, Ann. Miss. Bot. Gard. 97 (2010).

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’.

Contents