Origin and Habitat: Coryphantha macromeris subs. runyoniiSN|10026]]SN|10026]] has a small disjunct range along the lower river-course of the Rio Grande, at sea level, between Brownsville and Rio Grande City (Texas), and a parallel range on the opposite river side in the Mexican state of Tamaulipas.
Altitude range: It occurs only near sea level on the plain of the Rio Grande.

• Coryphantha macromeris subs. runyonii (Britton & Rose) N.P.Taylor
• Coryphantha macromeris var. runyonii (Britton & Rose) L.D.Benson
• Coryphantha runyonii Britton & Rose
• Lepidocoryphantha macromeris subs. runyonii (Britton & Rose) Doweld
• Lepidocoryphantha runyonii (Britton & Rose) Backeb.
• Mammillaria runyonii (Britton & Rose) Cory

• Coryphantha macromeris (Engelm. in Wisliz.) Lem.
• Cactus macromeris (Engelm. in Wisliz.) Kuntze
• Echinocactus macromeris
• Lepidocoryphantha macromeris (Engelm. in Wisliz.) Backeb.
• Mammillaria macromeris Engelm. in Wisliz.
• Coryphantha pirtlei Werderm.

• Coryphantha macromeris subs. runyonii (Britton & Rose) N.P.Taylor
• Coryphantha macromeris var. runyonii (Britton & Rose) L.D.Benson
• Coryphantha runyonii Britton & Rose
• Lepidocoryphantha macromeris subs. runyonii (Britton & Rose) Doweld
• Lepidocoryphantha runyonii (Britton & Rose) Backeb.
• Mammillaria runyonii (Britton & Rose) Cory

Description: Coryphantha macromerisSN|10268]]SN|10268]] is small plant profusely branched with long projecting spines, ultimately forming low mats or hemispheric mounds to 100 cm diameter. The ssp. runyonii is distinguishable for the grey-green stems up to 7.5 cm high and tubercles to 7.5 mm long.
Stem: Noticeably tuberculate, hemispheric to short cylindrical, sometimes obscured by profusion of immature branches, 4-12 cm; tubercles unusually large 15-25 mm and grooved only on the upper half, flaccid or flabby; areolar glands seasonally conspicuous;
Root: It has deep succulent taproot often massive and large.
Spines: Weakly appressed or projecting, slightly curved, often flexible. Radial 9-15 per areole, white, grey, tan, or brown, 15-25 mm long; subcentral spines 2-3 in adaxial part of areole; central spines 3-8 per areole, pale grey to black, abaxial central spine porrect or descending,
Flowers: Apical or nearly so at mid-level of tubercle, outer tepals heavily fringed; flower bright rose-pink or magenta, often with darker midstripes and paler margins
Fruits: Dark green, ovoid to obpyriform or ellipsoid.
Remarks: The flowers of C. macromeris are virtually identical to those of Mammillaria wrightiiSN|9411]]SN|9411]] and Escobaria viviparaSN|9953]]SN|9953]]: in the absence of vegetative material, flowers may be unidentifiable.

Bibliography: Major references and further lectures
1) Heil, K., Terry, M., Corral-Díaz, R., Lüthy, A.D. & Dicht, R.F. 2013. Coryphantha macromeris. The IUCN Red List of Threatened Species 2013: e.T152811A681352. http://dx.doi.org/10.2305/IUCN.UK.2013-1.RLTS.T152811A681352.en. Downloaded on 04 April 2016.
2) John Pilbeam (1999) “Mammillaria The Cactus File Handbook” Nuffield Press.
3) Edward F. Anderson “The Cactus Family” Timber Press, 2001
4) James Cullen, Sabina G. Knees, H. Suzanne Cubey “The European Garden Flora Flowering Plants: A Manual for the Identification of Plants Cultivated in Europe, Both Out-of-Doors and Under Glass” Cambridge University Press, 11/August/2011
5) Nathaniel Lord Britton, Joseph Nelson Rose “Cactaceae: Descriptions and Illustrations of Plants of the Cactus Family” vol. 4 The Carnegie Institution of Washington, Washington 1923
6) Benson, L. “The Cacti of the United States and Canada.” Stanford University Press, Stanford, California. 1982
7) Dicht, R.F. and Lüthy, A.D. “Coryphantha Cacti of Mexico and Southern USA.” Springer-Verlag, Berlin. 2003
8) David Hunt, Nigel Taylor “The New Cactus Lexicon” DH Books, 2006

Cultivation and Propagation: Coryphantha macromeris subs. runyoniiSN|10268]]SN|10026]] is popular with collectors and easy to grow. It comes from an area of summer rainfall. Keep drier in winter (but for outdoor cultivation it is quite resistant to wet conditions, too). Very cold resistant, hardy about to about -10° C, but the frost resistance varies a lot from clone to clone. Needs good drainage. Keep drier in winter, Full sun to partial shade.
Use and Trade: There are reports that Coryphantha macromerisSN|10026]]SN|10268]] (and in particular the subspecies runyonii) is collected for use as a hallucinogen. However, there is some debate about its psychoactive properties as the species does not contain mescaline like peyote, but instead has normacromerine, an analogue of epinephrine which seems to have potential hallucinogenic properties (Anderson 2001). This species may be used ceremonially in Mexico by the Tarahumara.
Propagation: Seeds (no dormancy requirement, they germinate best at 25°C) or by offsets (if available), or occasionally grafted.