| # The grass genera of the world |

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

### Arundo L.

From the Latin arundo, a reed.

Type species: Type: A. donax L.

Including Amphidonax Nees, Donacium Fries, Donax P. Beauv., Eudonax Fries, Scolochloa Mert. & Koch

Habit, vegetative morphology. Perennial; mostly reedy (with long canes); rhizomatous. The flowering culms leafy. Culms 200–600 cm high (or occasionally pendant from cliffs); woody and persistent; branched above (the main stems dominant), or unbranched above. The branching when branching, simple. Culm nodes glabrous. Culm internodes hollow. Young shoots extravaginal. Leaves not basally aggregated; auriculate, or non-auriculate. Leaf blades linear-lanceolate to lanceolate; broad; 25–80 mm wide; flat; not pseudopetiolate; without cross venation; disarticulating from the sheaths; rolled in bud. Ligule a fringed membrane (short). Contra-ligule absent.

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

Inflorescence. Inflorescence paniculate (plumose); open; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 12–18 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret, or terminated by a female-fertile floret; hairless (save above the floret abscission zones - i.e., on the callus); the rachilla extension (when present) with incomplete florets. Hairy callus present. Callus short; blunt.

Glumes two; more or less equal; about equalling the spikelets; long relative to the adjacent lemmas; pointed; awnless; carinate to non-carinate; similar (membranous). Lower glume 3–5 nerved. Upper glume 3–5 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets without proximal incomplete florets.

Female-fertile florets 2–7. Lemmas less firm than the glumes to similar in texture to the glumes (membranous or hyaline); not becoming indurated; entire, or incised; when incised, 2 lobed; not deeply cleft; awnless to awned. Awns when present, 1, or 3; median, or median and lateral; the median similar in form to the laterals (when laterals present); from a sinus; non-geniculate; much shorter than the body of the lemma; entered by one vein. The lateral awns (when present) shorter than the median. Lemmas villous hairy (on the back); non-carinate; 3–9 nerved. Palea present; relatively long to conspicuous but relatively short (from half to two thirds the lemma length); awnless, without apical setae; thinner than the lemma (delicately membranous), or textured like the lemma; 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 2.5–3.5 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; green to greyish.

Fruit, embryo and seedling. Fruit free from both lemma and palea. Hilum short. Embryo large. Endosperm containing compound starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Ovule, embryology. Micropyle oblique. Outer integument covering no more than the chalazal half of the ovule; more than two cells thick at the micropylar margin. Inner integument continuous, the micropyle constricted. Synergids not haustorial; without 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 (thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (54–)60–78(–81) microns long; 6.3–8.4 microns wide at the septum. Microhair total length/width at septum 9.6–11.9. Microhair apical cells 18–30 microns long. Microhair apical cell/total length ratio 0.33–0.35. Stomata common; 39–42–48 microns long. Subsidiaries dome-shaped, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; not paired (mainly solitary, sometimes in twos or threes); silicified (a few). Intercostal silica bodies tall-and-narrow, or cross-shaped, or saddle shaped, or oryzoid-type. Costal short-cells conspicuously in long rows (rarely), or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies ‘panicoid-type’; cross shaped to dumb-bell shaped.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma (rarely), or with non-radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles. Bulliforms present in discrete, regular adaxial groups; combining with colourless mesophyll cells to form narrow groups penetrating into the mesophyll. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Culm anatomy. Culm internode bundles in three or more rings.

Phytochemistry. Tissues of the culm bases with little or no starch. Leaves without flavonoid sulphates (1 species).

Special diagnostic feature. Female-fertile lemmas conspicuously hairy; ligule hairs to 0.3 mm long, shorter than the membrane.

Cytology. Chromosome base number, x = 12. 2n = 60, 72, 110, and 112. 6 and 9 ploid (and aneuploid). Chromosomes ‘small’. Nucleoli disappearing before metaphase.

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

Distribution, phytogeography, ecology. Tropical and temperate.

Commonly adventive. Helophytic to mesophytic.

Economic aspects. Significant weed species: A. donax, when blocking drainage ditches etc. Important native pasture species: A. donax. A. donax stems used for light construction work, and for making wood-wind reeds.

Rusts and smuts. Rusts — Dasturella and Puccinia.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - A. donax L.

Illustrations. • Arundo donax, as Donax arundinacea: P. Beauv. (1812). • Arundo donax: Bor, Fl. of Iraq (1968). • A. donax, general aspect: Gibbs Russell et al., 1990. • Arundo donax, transverse section of leaf blade: this project. Arundo donax. Bulliform cells and ‘colourless tissue’ constituting a narrow group penetrating the mesophyll.

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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