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The grass genera of the world

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

Cyclostachya J. & C. Reeder

From the Greek cyclo (a circle, or wheel) and stachya (‘ear of corn’, spike), alluding to the shape assumed by mature racemes.

~ Bouteloua sensu lato

Habit, vegetative morphology. Perennial; stoloniferous and caespitose. Culms 5–12 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes solid. Leaves mostly basal; non-auriculate; hairy in the auricle positions. Leaf blades linear (setaceous at the tip); narrow; to 1 mm wide; without abaxial multicellular glands; without cross venation; persistent. Ligule an unfringed membrane; not truncate (jagged); 0.5–1 mm long. Contra-ligule absent.

Reproductive organization. Plants dioecious; without hermaphrodite florets. The spikelets all alike in sexuality (on the same plant); female-only, or male-only. Plants outbreeding.

Inflorescence. Inflorescence (male and female) a single raceme (pectinate, curved, long pedunculate); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating; falling entire (the raceme finally recurving into a circle). Spikelets solitary; secund (pectinate, in two ranks); biseriate; pedicellate (on short pedicels).

Female-sterile spikelets. Male plants similar to females; male spikelets with one 3-stamened floret and 2–3 short-awned rudiments; glumes one-nerved; lemma 3-nerved, 3-toothed, short-awned; often with an abortive pistil. Rachilla of male spikelets prolonged beyond the uppermost male floret. The male spikelets with glumes; 1 floreted (plus rudiments). The lemmas short awned. Male florets 1; 3 staminate.

Female-fertile spikelets. Spikelets 8–9 mm long; compressed laterally to not noticeably compressed; disarticulating above the glumes (i.e., falling from the deciduous rachis). Rachilla prolonged beyond the uppermost female-fertile floret; hairy; the rachilla extension with incomplete florets. Hairy callus present.

Glumes two; very unequal (G1 about two-thirds of G2); (the upper) long relative to the adjacent lemmas; dorsiventral to the rachis; hairy (G2); pointed (G1 lanceolate-acuminate), or not pointed (G2 apically notched); G2 with 1–3 apical setae; carinate (G1), or non-carinate (G2); very dissimilar (hyaline, G1 carinate-acuminate, glabrous, G2 2-keeled, 2–3 lobed or notched at apex, with hairs on the back). Lower glume 1 nerved. Upper glume 2 nerved, or 3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 2–3; clearly specialised and modified in form (clustered at the tip of the rachilla, their scabrid awns much longer than those of the fertile lemma); each three awned.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes (membranous or cartilaginous); not becoming indurated; incised; 3 lobed; deeply cleft (into the awns); awned. Awns 3; median and lateral (via the acuminate lobes); the median more or less similar in form to the laterals (but not bending back); from a sinus, or apical (depending on interpretation, the three lobes acuminate into the awns); non-geniculate; hairless (scabrid); much shorter than the body of the lemma to about as long as the body of the lemma; entered by one vein. The lateral awns shorter than the median (bending back). Lemmas hairy; slightly keeled on the three nerves; without a germination flap; 3 nerved. Palea present (similar to the two-nerved examples of G2); relatively long; apically notched; with apical setae (2, asymmetric, via the excurrent nerves); not indurated (hyaline to membranous, with green tissue); 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 0 (3 staminodes only). Ovary apically glabrous. Styles free to their bases. Stigmas 2; stigmas pigmented.

Fruit, embryo and seedling. Fruit small (3 mm long); ellipsoid; not noticeably compressed. Hilum short. Pericarp fused. Embryo large; waisted; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (costals narrower); of similar wall thickness costally and intercostally (rather thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (and pitted). Microhairs present; elongated; clearly two-celled; chloridoid-type (very large). Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs (33–)34.5–36(–39) microns long. Microhair basal cells 21–24 microns long. Microhairs 12–15 microns wide at the septum. Microhair total length/width at septum 2.4–2.9. Microhair apical cells 10.5–16.5 microns long. Microhair apical cell/total length ratio 0.3–0.48. Stomata common; 24–25.5 microns long. Subsidiaries dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies present and perfectly developed; tall-and-narrow and saddle shaped. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; predominantly saddle shaped.

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

C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. Mesophyll traversed by columns of colourless mesophyll cells. Leaf blade ‘nodular’ in section (with prominent, flattish abaxial ribs); with the ribs more or less constant in size (slight). Midrib conspicuous (larger bundle and rib, and a large abaxial anchor-shaped girder); with one bundle only. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these associated with the colourless girders). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (adaxial strands only, the PCA tissue encircling the top of each bundle; abaxial strands or girders). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Boutelouinae (as a synonym of Bouteloua). 1 species.

Distribution, phytogeography, ecology. Mexico.

Species of open habitats. Dry places.

References, etc. Morphological/taxonomic: Reeder and Reeder 1963. Leaf anatomical: this project.

Illustrations. • Cyclostachya stolonifera (as Bouteloua): Griffiths, Cont. U.S. Nat. Herb. 14 (1912). • C. stolonifera, 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: 13th November 2017. delta-intkey.com/grass’.

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