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From the Latin arundo (a reed) and -ella (diminutive suffix).
Type species: Type: A. brasiliensis Raddi.
Including Acratherum Link, Brandtia Kunth, Calamochloe Reichenb., Goldbachia Trin., Riedelia Kunth, Thysanachne Presl
Habit, vegetative morphology. Annual, or perennial; mostly with tough, erect culms. Culms 30–150 cm high; herbaceous; branched above, or unbranched above (commonly). The branching when branching, simple, or fastigiate (rarely). Culm nodes glabrous. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; not setaceous (rigid); flat, or rolled; not pseudopetiolate; without cross venation; disarticulating from the sheaths, or persistent; rolled in bud. Ligule a fringed membrane (narrow); truncate.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and sterile (sterile spikelets, when present, very reduced).
Inflorescence. Inflorescence paniculate; open, or contracted; with capillary branchlets, or without capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary, or paired; not secund; pedicellate; consistently in ‘long-and-short’ combinations, or not in distinct ‘long-and-short’ combinations. The ‘shorter’ spikelets hermaphrodite, or sterile (sometimes reduced to a glume). The ‘longer’ spikelets hermaphrodite.
Female-fertile spikelets. Spikelets 1.5–8 mm long; compressed laterally; disarticulating above the glumes, or disarticulating above the glumes and falling with the glumes (at least sometimes both); always disarticulating between the florets (but not between the upper glume and the lower floret). Rachilla terminated by a female-fertile floret. Hairy callus present. Callus short; blunt.
Glumes two; very unequal; (the upper) long relative to the adjacent lemmas; pointed; awned, or awnless; very dissimilar to similar (membranous to papery, G1 acute to mucronate, G2 often caudate). Lower glume 3 nerved. Upper glume 5 nerved. Spikelets with incomplete florets (or rarely both florets perfect). The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed (narrow, two keeled). The proximal incomplete florets male. The proximal lemmas awnless; 3–7 nerved; less firm than the female-fertile lemmas to similar in texture to the female-fertile lemmas; not becoming indurated.
Female-fertile florets 1(–2). Lemmas similar in texture to the glumes to decidedly firmer than the glumes (membranous to thinly leathery); not becoming indurated; entire, or incised; when entire pointed, or blunt; when incised, 2 lobed; not deeply cleft (entire, emarginate or bilobed); awnless, or awned. Awns 1 (usually), or 3; median, or median and lateral (via capillary bristles from the lobes); the median different in form from the laterals (when laterals present); from a sinus; geniculate; hairless; much shorter than the body of the lemma to much longer than the body of the lemma; persistent. Lemmas hairless (scabrid or scabridulous); non-carinate; having the margins lying flat on the palea, or having the margins inrolled against the palea; with a clear germination flap; 1–7 nerved. Palea present; entire (narrow); awnless, without apical setae; not indurated; 2-nerved; 2-keeled. Palea keels wingless (the margins sometimes auriculate below). Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 1.5–2 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white, or red pigmented, or brown.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed dorsiventrally, or not noticeably compressed. Hilum short. Embryo large; waisted. Endosperm hard; without lipid; containing compound starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
Seedling with a long mesocotyl.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (36–)38–60(–62) microns long. Microhair apical cells (18–)21–42(–44) microns long. Microhair apical cell/total length ratio 0.56–0.67. Stomata common. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies tall-and-narrow, or crescentic. Costal short-cells predominantly paired. Costal silica bodies rounded (e.g. A. nepalensis), or crescentic (sometimes), or ‘panicoid-type’ (commonly); when panicoid type, cross shaped to dumb-bell shaped.
Transverse section of leaf blade, physiology. C4. The anatomical organization conventional, or unconventional. Organization of PCR tissue when unconventional Arundinella type. Biochemical type NADP–ME (A. nepalensis); XyMS–. PCR sheath outlines uneven. PCR sheath extensions present. Maximum number of extension cells 1. PCR cells with a suberised lamella. PCR cell chloroplasts ovoid; with reduced grana (rudimentary); centrifugal/peripheral. Mesophyll with radiate chlorenchyma; exhibiting ‘circular cells’, or without ‘circular cells’. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles. Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.
Culm anatomy. Culm internode bundles in one or two rings.
Phytochemistry. Leaf blade chlorophyll a:b ratio 4.45–4.51.
Cytology. Chromosome base number, x = 7, 10, 12, and 14. 2n = 14, 20, 28, 36, and 56. Chromosomes ‘small’.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Arundinelleae. Soreng et al. (2015): Panicoideae; Andropogonodae; Arundinelleae. 55 species.
Distribution, phytogeography, ecology. In warm regions.
Commonly adventive. Helophytic to mesophytic; species of open habitats; glycophytic. Marshy places, riverbanks and rocky slopes.
Economic aspects. Significant weed species: A. bengalensis, A. leptochloa (in North America). Important native pasture species: A. setosa.
Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia coronata. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Tilletia. Ustilaginaceae — Sorosporium, Sphacelotheca, and Ustilago.
References, etc. Leaf anatomical: Metcalfe 1960; studied by us - A. nepalensis Trin.
Illustrations. • Arundinella holcoides, as Brandtia: Kunth (1835). • Arundinella nepalensis: Gardner, 1952. • A. nepalensis: Gibbs Russell et al., 1990. • Spikelets of A. nepalensis. • Spikelet details (A. nepalensis). Arundinella nepalensis. Female-fertile floret (with awned lemma) to the left. • Arundinella nepalensis, abaxial epidermis of leaf blade: this project. • A. nepalensis, abaxial epidermis of leaf blade: this project. • Arundinella nepalensis, T.S. leaf blade: this project. • A. nepalensis leaf blade T.S. with immunofluorescent-labelled Rubisco: (Hattersley, Watson and Osmond 1977. Immunofluorescent-labelled RuBISCO, showing isolated PCR cells additional to those of the sheaths. See Hattersley, Watson and Osmond (1977). • Arundinella nepalensis, T.S. leaf blade fluorescence image: Hattersley, Watson and Osmond (1977).. See Hattersley, Watson and Osmond (1977).
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: 25th January 2024. delta-intkey.com’.
