| # The grass genera of the world |

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

### Oligostachyum Z.P. Wang & G.H. Ye

~ Arundinaria

Including Clavinodum T.H. Wen

Habit, vegetative morphology. Shrubby to arborescent, perennial. The flowering culms leafy. Culms 76–1300 cm high; woody and persistent (without nodal roots); cylindrical to flattened on one side (semiterete), or flattened on one side (flattened or channelled above the branches); branched above. Primary branches thinner than the stem, (2–)3, or 3–7; horizontally aligned. The branching dendroid (the branches subequal, or one dominant). Culm nodes flush with the internodes, swollen or flanged, sometimes with a supranodal ridge. Culm leaf sheaths present; where recorded, deciduous; conspicuously auriculate, or not conspicuously auriculate. Culm leaves with conspicuous blades. Culm leaf blades linear, or lanceolate, or triangular. Rhizomes leptomorph. Leaves auriculate (erect or falcate), or non-auriculate; with auricular setae to without auricular setae. Leaf blades herbaceous or chartaceous, small, linear to lanceolate, or elliptic; pseudopetiolate; cross veined; disarticulating from the sheaths, or persistent. Ligule an unfringed membrane, or a fringed membrane.

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

Inflorescence. Inflorescence determinate, or indeterminate; with pseudospikelets (with or without basal axillary buds), or without pseudospikelets; few spikeleted to many spikeleted; of spicate main branches (with few spikelets), or paniculate (with many); open; spatheate (subtending by an unspecialized leaf sheath or a spatheole); a complex of ‘partial inflorescences’ and intervening foliar organs (with glumaceous or spathaceous subtending bracts), or not comprising ‘partial inflorescences’ and foliar organs. Spikelets solitary; not secund; sessile (rarely), or subsessile.

Female-fertile spikelets. Spikelets morphologically ‘conventional’, or unconventional; 15–80 mm long; lanceolate, or elliptic, or linear (commonly); compressed laterally; disarticulating above the glumes; disarticulating between the florets; with distinctly elongated rachilla internodes between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairy to hairless; the rachilla extension with incomplete florets.

Glumes persistent, one per spikelet (rarely), or several (usually 3–5); very unequal to more or less equal; shorter than the spikelets; hairless; glabrous, or scabrous; pointed, or pointed and not pointed (usually acute, the upper sometimes blunt); muticous or mucronate, awnless; carinate, or non-carinate; chartaceous, lanceolate or elliptic, the upper sometimes ovate, more or less similar. Lower glume 0.5–1 times the length of the upper glume; much shorter than half length of lowest lemma to longer than half length of lowest lemma; 7–9 nerved. Upper glume 7–11 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets, or both distal and proximal to the female-fertile florets (the ‘transitional glumes’ then subtending sterile paleate florets). The distal incomplete florets merely underdeveloped. The proximal incomplete florets 1, or 2; when present, paleate. Palea of the proximal incomplete florets fully developed to reduced. The proximal incomplete florets sterile.

Female-fertile florets (3–)5–13. Lemmas lanceolate, elliptic or ovate; chartaceous, similar in texture to the glumes; smooth; not becoming indurated; entire; pointed, or blunt (obtuse, acute, acuminate or setaceously attenuate); awnless, or mucronate (mostly), or awned. Awns when present, 1; median; apical; non-geniculate. Lemmas hairy to hairless; with tessellate venaztion, 7–15(–17) nerved. Palea present; relatively long to conspicuous but relatively short; entire to apically notched; membranous to chartaceous, thinner than the lemma to textured like the lemma; not indurated; 1-nerved, or several nerved (9 or 15); 2-keeled. Palea back glabrous to hairy. Palea keels glabrous to hairy. Lodicules present; mostly 3 (the anterior pair usually asymmetrical); membranous; ciliate, or glabrous; heavily vascularized (5–7 veined). Stamens 3 (mostly), or 3–5 (rarely, never 6). Ovary usually apically glabrous; with a conspicuous apical appendage, or without a conspicuous apical appendage. The appendage where recorded, broadly conical, fleshy. Styles fused. Stigmas plumose, (2–)3.

Fruit, embryo and seedling. Fruit not apically appendaged. Pericarp thin.

Classification. Watson & Dallwitz (1994): genus not recognised. Soreng et al. (2015): Bambusoideae; Arundinarodae; Arundinarieae; Arundinariinae. 16 species.

Distribution, phytogeography, ecology. Temperate Asia.

References, etc. Morphological/taxonomic: Wang & Ye (1982), Flora of China 22, 127; Clayton et al. (2016), Grassbase.

Special comments. Differing noticeably from Acidosasa in having florets with no more than 5 stamens. Anatomical data wanting.

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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