| # The grass genera of the world |

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

### Diarrhena P. Beauv.

From the Greek dis (twice) and arren (male), alluding to two stamens.

Including Diarina Raf., Korycarpus Lag., Neomolinia Honda, Onoea Franch. & Sav., Roemeria Roem. & Schult.

Habit, vegetative morphology. Large perennial; rhizomatous. Culms 50–150 cm high; herbaceous. Culm nodes nodes concealed. Leaves non-auriculate. Leaf blades broad; 1–2 mm wide; pseudopetiolate to not pseudopetiolate; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane (but sometimes minutely ciliolate); 0.5–1 mm long.

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

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

Female-fertile spikelets. Spikelets 2.8–18 mm long (2.8–7 mm in Neomolinia, 10–18 mm in Diarrhena sensu stricto); compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; spinulose or smooth. Hairy callus absent.

Glumes two; very unequal; shorter than the spikelets; shorter than the adjacent lemmas; pointed, or not pointed (obtuse to acuminate); awnless; carinate. Lower glume 1–3 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.

Female-fertile florets 2–3 (rarely 1 or 5). Lemmas decidedly firmer than the glumes; becoming indurated (horny); entire; blunt; awnless to mucronate; hairless (scabrous or glabrous); non-carinate (rounded on the back); 3–5 nerved. Palea present; relatively long; textured like the lemma (horny); indurated; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; apically ciliate; toothed, or not toothed; not or scarcely vascularized. Stamens (1–)2–3. Anthers 1.2–2.2 mm long; not penicillate. Ovary apically glabrous (though the rostellum is scabrous in Neomolinia); with a conspicuous apical appendage (in the form of an apical beak, the styles attached terminally in its groove). Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; medium sized (about 5 mm long); compressed laterally, or not noticeably compressed (with a whitish or yellowish-glossy, sometimes enlarged and hardened beak); surface rough but not sculptured. Hilum short, or long-linear (short- or long-linear, from one third to as long as grain). Pericarp free. Embryo small (1/4 to 1/3 of grain length). Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast; with a scutellar tail, or without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting (Reeder 1957), or overlapping (Macfarlane and Watson 1980).

Seedling with a short mesocotyl. First seedling leaf with a well-developed lamina. The lamina narrow (broader towards the tip); erect; 7 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals relatively longer and narrower). Mid-intercostal long-cells rectangular to fusiform; having markedly sinuous walls. Microhairs present (D. mandshurica - see Renvoize 1985), or absent; as figured, more or less spherical (cf. Hygroryza, Luziola etc.?); ostensibly one-celled; obscure and hard to interpret. Stomata common. Subsidiaries low dome-shaped, or parallel-sided. Guard-cells slightly overlapped by the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies rounded, crescentic, tall-and-narrow, and cubical, or vertically elongated-nodular. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous, or ‘panicoid-type’; when panicoid type, cross shaped, or butterfly shaped, or dumb-bell shaped, or nodular.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without arm cells; without fusoids. Leaf blade adaxially flat. Midrib conspicuous (with a big keel and massive blocks of sclerenchyma, at least in D. americana); having a conventional arc of bundles (the median being very large). Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’, or nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. Grain with a conspicuous whitish or yellowish, glossy beak.

Cytology. Chromosome base number, x = 10 and 19. 2n = 38 and 60. 2 and 6 ploid. Chromosomes ‘medium sized’.

Classification. Watson & Dallwitz (1994): dubiously Bambusoideae (or Stipoideae?); Oryzodae (?); Diarrheneae. Soreng et al. (2015): Pooideae; Diarrheneae. 4–5 species.

Distribution, phytogeography, ecology. Eastern Asia, North America.

Shade species.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis.

References, etc. Morphological/taxonomic: Tateoka 1957b; Schwab 1972; Macfarlane and Watson 1980. Leaf anatomical: Metcalfe 1960; studied by us - D. americana P. Beauv., D. japonica Franch. & Savat., D. mandshurica Maxim. (~ Neomolinia).

Illustrations. • Diarrhena americana: P. Beauv. (1812). • Diarrhena americana: Hitchcock and Chase (1950). • Diarrhena americana, abaxial epidermis of leaf blade: this project.

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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