| # The grass genera of the world |

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

### Eustachys Desf.

From the Greek eu (good or nice) and stachys (‘ear of wheat’, spike), the numerous spikes and dark brown lemmas rendering the inflorescence distinctive.

Type species: Type: E. petraea (Sw.) E.Desv.

Including Chloroides Regel, Langsdorffia Regel, Schultesia Spreng.

Habit, vegetative morphology. Annual, or perennial; caespitose. Culms 20–100 cm high; herbaceous; unbranched above (where recorded). Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. The sheaths laterally folded and keeled. Leaf blades linear; broad, or narrow; flat, or folded; without abaxial multicellular glands; pseudopetiolate, or not pseudopetiolate; without cross venation; persistent. Ligule a fringe of hairs.

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.

Inflorescence. Inflorescence of spicate main branches (pectinate spikes or spicate racemes); digitate. Primary inflorescence branches 2–45. Rachides hollowed, or flattened (or angular). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund; biseriate.

Female-fertile spikelets. Spikelets 1.7–5 mm long; adaxial; compressed laterally to not noticeably compressed; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two; relatively large (thinly membranous); very unequal to more or less equal; about equalling the spikelets; shorter than the adjacent lemmas; dorsiventral to the rachis; hairless; scabrous; not pointed (notched or blunt); the upper awned (from below its apex); carinate; very dissimilar (both membranous, but the G2 broader and awned). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets usually 2; merely underdeveloped (greatly reduced, or the lower male). Spikelets without proximal incomplete florets.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes (firmly membranous to leathery); not becoming indurated; dark brown in fruit; entire, or incised; when incised, 2 lobed; not deeply cleft (notched); awnless, or mucronate; hairy (on margins and keel); carinate; 3 nerved. Palea present; entire (oblanceolate); awnless, without apical setae; thinner than the lemma (scarious); not indurated; 2-nerved; 2-keeled. Palea keels winged (and ciliolate). Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; ellipsoid; trigonous. Hilum short. Pericarp loosely adherent, or fused. Embryo large; not waisted.

Ovule, embryology. Micropyle oblique. Outer integument extensive, being absent only from the micropylar region; two cells thick at the micropylar margin. Inner integument continuous, the micropyle constricted; thickened around the micropyle. Synergids not haustorial; without large, globular starch grains.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae over-arching the stomata; consisting of one oblique swelling per cell, or several per cell (usually with two diverging, oblique swellings). Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Intercostal zones with typical long-cells (though these rather short). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical; ostensibly one-celled; chloridoid-type; 18–22 microns long. Stomata common; (18–)28–30 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired; not silicified. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; saddle shaped.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; biochemical type NAD–ME (E. distichophylla); XyMS+. PCR sheath outlines uneven, or even. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions absent. PCR cell chloroplasts centrifugal/peripheral, or centripetal. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous (with a large adaxial bulliform group); with one bundle only; with colourless mesophyll adaxially (this extending across the lamina and adaxial to most of the bundles). Bulliforms present in discrete, regular adaxial groups (more or less, but the groups large, occupying most of the intercostal regions, and separated by few smaller epidermal cells from the colourless and bulliform tissue adaxial to the vascular bundles); associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 10. 2n = 40. 4 ploid.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae. 10 species.

Distribution, phytogeography, ecology. Tropical America, West Indies, tropical and South Africa.

Commonly adventive. Mesophytic; species of open habitats; glycophytic. Savanna, on a variety of soils.

Economic aspects. Important native pasture species: E. paspaloides.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - E. distichophylla (Lag.) Nees.

Illustrations. • General aspect of Eustachys paspaloides: Gibbs Russell et al., 1990. • Eustachys distichophylla: Kunth (1835). • Eustachys distichophylla, abaxial epidermis of leaf blade: this project. • Abaxial epidermis of leaf blade of Eustachys distichophylla, detail of silica bodies).

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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