| # The grass genera of the world |

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

### Anthoxanthum L.

From the Greek anthos (flower) and xanthos (yellow), referring to panicle colour after flowering.

Type species: Type: A. odoratum L.

Including Flavia Fabric., Foenodorum Krause, Xanthonanthus St-Lager

Excluding Hierochloë

Habit, vegetative morphology. Annual, or perennial; caespitose to decumbent. Culms 5–90 cm high; herbaceous; sparingly branched above, or unbranched above. Culm nodes hairy, or glabrous. Culm internodes hollow. The shoots aromatic (coumarin-scented). Leaves not basally aggregated; non-auriculate. Leaf blades linear to lanceolate; broad, or narrow (2–15); flat; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane; not truncate; 2–5 mm long.

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

Inflorescence. Inflorescence a single raceme (rarely), or paniculate; contracted; more or less ovoid, or spicate. Primary inflorescence branches inserted all around the main axis. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; sessile to pedicellate.

Female-fertile spikelets. Spikelets 5–10 mm long; compressed laterally; disarticulating above the glumes. Rachilla terminated by a female-fertile floret.

Glumes two; very unequal; (the upper) long relative to the adjacent lemmas; pointed; awnless; carinate; similar (membranous). Lower glume 1 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 2; paleate (sometimes, the palea two-keeled), or epaleate; sterile. The proximal lemmas awned; 3 nerved; decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas (hairy); not becoming indurated.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes; becoming indurated; entire, or incised; awnless, or awned. Awns when present, 1; geniculate; much shorter than the body of the lemma to much longer than the body of the lemma. Lemmas hairless; non-carinate; 1–7 nerved. Palea present; relatively long; entire; awnless, without apical setae; not indurated; 1-nerved, or 2-nerved, or nerveless; keel-less. Lodicules absent. Stamens 2, or 3 (rarely). Anthers 3.5–5 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small. Hilum short. Embryo small; not waisted. Endosperm hard; with lipid; containing compound starch grains. Embryo with an epiblast; with a scutellar tail to without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

Seedling with a long mesocotyl; with a tight coleoptile. First seedling leaf with a well-developed lamina. The lamina narrow; 3 veined.

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 fusiform; having markedly sinuous walls. Microhairs absent. Stomata common; about 36 microns long (in A. odoratum). Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous, or horizontally-elongated smooth, or rounded.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section; with the ribs more or less constant in size. Midrib conspicuous; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (or the cells fairly regular in size). 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 one or two rings.

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

Cytology. Chromosome base number, x = 5. 2n = 10 and 20. 2 and 4 ploid. Chromosomes ‘large’. Mean diploid 2c DNA value 11.8 pg (A. odoratum).

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Anthoxanthinae. 20 species.

Distribution, phytogeography, ecology. North temperate & mountains of tropical Africa & Asia.

Commonly adventive. Mesophytic; shade species and species of open habitats. Meadows, grasslands and in light shade.

Economic aspects. Significant weed species: A. aristatum, A. odoratum.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis, Puccinia coronata, Puccinia brachypodii, and Puccinia recondita. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Tilletia and Urocystis. Ustilaginaceae — Ustilago.

References, etc. Morphological/taxonomic: Schouten and Veldkamp 1985. Leaf anatomical: Metcalfe 1960; studied by us - A. odoratum L.

Special comments. Should perhaps include Hierochloë.

Illustrations. • Anthoxanthum odoratum: Gardner, 1952. • A. odoratum: Eng. Bot. (1872). • A. ecklonii, general aspect: Gibbs Russell et al., 1990. • Ligule region (A. odoratum). • Spikelets (A. odoratum). • Spikelets (A. odoratum). • Spikelet details (A. odoratum). • Grass pollen antigens: Watson and Knox (1976).

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