| # The grass genera of the world |

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

### Monostachya Merr.

~ Rytidosperma, Danthonia sensu lato

Habit, vegetative morphology. Perennial; low, mat-forming alpines. Culms 2–20 cm high (?); herbaceous. Culm nodes glabrous. Culm internodes hollow. Leaves mostly basal; non-auriculate. Leaf blades narrow; setaceous; without cross venation; persistent. Ligule a fringed membrane.

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 (having vestigial spikelets, much reduced, beneath the terminal perfect one).

Inflorescence. Inflorescence reduced to a single spikelet, or few spikeleted; if of more than one spikelet a single raceme; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets compressed laterally; disarticulating above the glumes; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairless. Hairy callus present, or absent.

Glumes two; more or less equal; long relative to the adjacent lemmas; awnless; similar. Lower glume 3 nerved. Upper glume 3 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets.

Female-fertile florets 1–10. Lemmas not becoming indurated; incised; 2 lobed; mucronate, or awned. Awns when present, from a sinus; non-geniculate; when present, much shorter than the body of the lemma. Lemmas hairless; non-carinate; 3–5 nerved. Palea present; 2-nerved. Lodicules present; free; fleshy; ciliate. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit small; compressed laterally. Hilum short. Embryo small; not waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (with paired short-cells costally). Papillae absent. Long-cells similar in shape costally and intercostally (long-rectangular); of similar wall thickness costally and intercostally (walls thick and sinuous). Mid-intercostal long-cells having markedly sinuous walls. Microhairs absent (but present adaxially); panicoid type. Stomata absent or very rare (abaxially, but present adaxially). Subsidiaries not available abaxially, but triangles and domes present adaxially. Intercostal short-cells common; in cork/silica-cell pairs; not silicified (usually). Costal short-cells predominantly paired. Costal silica bodies rounded; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 5. 2n = 20. 4 ploid.

Classification. Watson & Dallwitz (1994): Arundinoideae; Danthonieae. Soreng et al. (2015): Danthonioideae; Danthonieae. About 4 species.

Distribution, phytogeography, ecology. Philippines, New Guinea.

Shade species. In humid places.

References, etc. Morphological/taxonomic: Jacobs 1982. Leaf anatomical: studied by us - M. oreoboloides (F. Muell.) Hitchc.

Illustrations. • Monostachya oreoboloides (as Danthonia): Hook. Ic. Pl. 27 (1901). • Monostachya oreoboloides, 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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