| # The grass genera of the world |

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

### Rytidosperma Steud. sensu stricto

From the Greek rhytis (wrinkle) and sperma (seed), referring to the back of a larvae mistaken for the seed.

~ Danthonia sensu lato, Notodanthonia

Type species: Type: R. lechleri Steud.

Including Erythranthera Zotov, Monostachya Merr., Notodanthonia Zotov p.p., Pyrrhanthera Zotov

Excluding Austrodanthonia, Chionochloa, Joycea, Karroochloa, Merxmuellera, Monachather, Notodanthonia p.p., Plinthanthesis

Habit, vegetative morphology. Perennial; caespitose. Culms 2–56 cm high; herbaceous; branched above, or unbranched above; 1–4 noded. Culm nodes exposed; glabrous. Culm internodes solid, or hollow. Young shoots extravaginal, or intravaginal. Leaves mostly basal, or not basally aggregated (more often); non-auriculate. Leaf blades linear, or linear-lanceolate; narrow; 0.1–4 mm wide; setaceous, or not setaceous; flat, or folded, or rolled, or acicular; hard, woody, needle-like (rarely), or not needle-like; exhibiting multicellular glands abaxially. The abaxial leaf blade glands intercostal. Leaf blades not pseudopetiolate; without cross venation; disarticulating from the sheaths, or persistent; once-folded in bud. Ligule a fringed membrane (very short), or a fringe of hairs; 0.5–5 mm long. Contra-ligule present, or absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality. Plants inbreeding; exposed-cleistogamous, or chasmogamous; without hidden cleistogenes.

Inflorescence. Inflorescence rarely reduced to a single spikelet, or few spikeleted (usually), or many spikeleted; paniculate (sometimes almost a raceme, or reduced to a single spikelet); open to contracted (frequently open at anthesis, then closing when fruiting); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 3–17 mm long; cuneate, or obovate; green to purple; compressed laterally; disarticulating above the glumes; disarticulating between the florets (the disarticulations oblique); with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus present. The callus hairs white. Callus short; blunt.

Glumes two; more or less equal; about equalling the spikelets, or exceeding the spikelets; long relative to the adjacent lemmas; usually hairy, or hairless (rarely); scabrous; pointed (acute); awnless; keeled above; similar (papery, persistent). Lower glume 5–7 nerved. Upper glume 5–7 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets when present, as is usual, distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.

Female-fertile florets 2–8. Lemmas similar in texture to the glumes (soft to leathery); not becoming indurated; entire, or incised; pointed; 2 lobed (the lobes acute, acuminate or setaceous, often partially fused to the awn base); deeply cleft, or not deeply cleft; rarely mucronate, or awned. Awns 1, or 3; median, or median and lateral; the median different in form from the laterals (when laterals present); from a sinus; non-geniculate, or geniculate; much shorter than the body of the lemma to much longer than the body of the lemma; entered by several veins. The lateral awns (when present) shorter than the median to about equalling the median (straight, terminating the lobes). Lemmas nearly always hairy (though there are a few exceptions). The hairs when present (as is usual), in tufts; in transverse rows (usually with transverse rows of tufts, or as two marginals tufts). Lemmas non-carinate (rounded on the back); without a germination flap; 7–9 nerved; with the nerves confluent towards the tip. Palea present; relatively long; entire (truncate), or apically notched (minutely bilobed); awnless, without apical setae; thinner than the lemma; not indurated (membranous, or firm towards the base); 2-nerved; 2-keeled. Palea back glabrous, or hairy. Palea keels wingless; scabrous. Lodicules present; 2; free; fleshy; ciliate; not or scarcely vascularized. Stamens 3. Anthers 0.3–3 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases; free. Style bases widely separated. Stigmas 2; white, or red pigmented, or brown.

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 (or somewhat hollowed); compressed dorsiventrally; glabrous; smooth. Hilum short (usually punctiform). Pericarp thin; fused. Embryo large; waisted; without an epiblast; with a scutellar tail; with an elongated mesocotyl internode.

Ovule, embryology. Micropyle not noticeably oblique. Outer integument covering no more than the chalazal half of the ovule; more than two cells thick at the micropylar margin. Inner integument discontinuous distally; not thickened around the micropyle. Synergids haustorial (strongly developed); exhibiting large, globular starch grains.

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. Intercostal zones with typical long-cells. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present, or absent; panicoid-type, or chloridoid-type; 45–54–66 microns long; 9.6–18.22–26.4 microns wide at the septum. Microhair total length/width at septum 1.8–3.325–5.8. Microhair apical cells 13.5–24.75–36 microns long. Microhair apical cell/total length ratio 0.3–0.4425–0.59. Stomata common, or absent or very rare; 39–43.5–48 microns long. Subsidiaries dome-shaped, or triangular; not including both parallel-sided and triangular forms on the same leaf. Guard-cells overlapped by the interstomatals, or overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified, or not silicified. Intercostal silica bodies crescentic. Crown cells absent. Costal zones with short-cells. Costal short-cells conspicuously in long rows, or predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies rounded, or crescentic, or ‘panicoid-type’; cross shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. Leaf blades ‘laminar’.

C3; XyMS+. Mesophyll with radiate chlorenchyma, or with non-radiate chlorenchyma; without adaxial palisade; not Isachne-type; without ‘circular cells’; not traversed by colourless columns; without arm cells; without fusoids. Leaf blade with distinct, prominent adaxial ribs, or adaxially flat; with the ribs more or less constant in size. Midrib conspicuous, or not readily distinguishable; with one bundle only; without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups; in simple fans; nowhere involved in bulliform-plus-colourless mesophyll arches. Many of the smallest vascular bundles unaccompanied by sclerenchyma, or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 6. 2n = 24, 48, 72, 96, and 120. 4–20 ploid.

Classification. Watson & Dallwitz (1994): Arundinoideae; Danthonieae. Soreng et al. (2015): Danthonioideae; Danthonieae. 35 species.

Distribution, phytogeography, ecology. Australasian region, and perhaps also South America.

Helophytic, or mesophytic; mostly species of open habitats; glycophytic. Generally open, upland, grasslands, mires or rocky habitats.

References, etc. Morphological/taxonomic: Rytidosperma as re-circumscribed by H.P. Linder, who provided the description (1997: excluding anatomy). Leaf anatomical: data temporarily restricted to the included genera, Erythranthera, Monostachya, and Pyrrhanthera, pending reorganization of the anatomical description of Rytidosperma sensu Linder.

Illustrations. • Rytidosperma caespitosum, as Danthonia: Kunth (1835). • Rytidosperma gracile (as Danthonia): Hooker, Fl. Novae-Zelandiae (1853). • Rytidosperma setaceum (as Danthonia): Hooker, Fl. Tasmaniae (1860). • Rytidosperma pauciflorum (as Danthonia): Hooker, Fl. Tasmaniae (1860). • Rytidosperma caespitosum: Linder et al, Ann. Miss. Bot. Gard. 97 (2010). • Rytidosperma carphoides, as Danthonia: Turner, Austr. Grasses (1895). • Rytidosperma carphoides, abaxial epidermis of leaf blade: this project. • R. carphoides, abaxial epidermis of leaf blade: this project. • Rytidosperma dimidiata, abaxial epidermis of leaf blade: this project. • Rytidosperma nivicola, abaxial epidermis of leaf blade: this project. • R. nivicola, abaxial epidermis of leaf blade: this project. • Rytodosperma procera, abaxial epidermis of leaf blade: this project. • procera, abaxial epidermis of leaf blade: this project. • Rytidosperma nudiflora, abaxial epidermis of a leaf blade with external pitting. • Rytidosperma (Monostachya) oreoboloides, abaxial epidermis of leaf blade: this project. • Abaxial epidermis of leaf blade of Rytidosperma (Monostachya) oreoboloides: this project. • Abaxial epidermis of leaf blade of Rytidosperma (Pyrrhanthera) exigua: this project. • Abaxial epidermis of leaf blade of Rytidosperma (Pyrrhanthera) exigua. • ‘Panicoid-type’ microhairs of Rytidosperma linkii and Peudosasa japonica: longitudinal EM sections (Amarasinghe). Longitudinal sections showing ultrastructure of ‘panicoid-type’ microhairs of Pseudosasa japonica (Figs. 26–28) and Rytidosperma linkii (29–30). BC = basal cell, CC = cap cell, CW = cell wall, D = dictyosomes, M = mitochondria, N = nucleus, OS = osmophilic material, PM = plasma membrane, RER = rough endoplasmic reticulum. Scale bars: Fig. 26, 1.5 microns; 27, 1 micron; 28, 0.1 micron; 29, 2 microns; 30, 1 micron.

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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