Species and material from Yucatán
Plants of the World Online accepts Mammillaria heyderi Muehlenpf. and the subspecies heyderi and gaumeri. The name Mammillaria gaumeri (Britton & Rose) Orcutt is a synonym of M. heyderi subsp. gaumeri (Britton & Rose) D.R.Hunt. This subspecies occurs in Mexico, in Veracruz, Yucatán and Quintana Roo. Cervera and colleagues' 2007 study concerned this Yucatán material of subspecies gaumeri (M. gaumeri in the paper). [2-WWW]
The natural range of the whole species is broader than that of subspecies gaumeri and also includes the southern United States and other parts of Mexico. Assigning the measurements described below to Yucatán populations preserves their proper geographical and taxonomic scope. [2-WWW] [Cervera et al. 2007, POWO, 11 October 2026. Cervera et al., pp. 620–622]
Two environments and seasonality
Plants were observed in 2003–2004 in coastal dune scrub at San Benito and in seasonally deciduous tropical forest at Ría Lagartos. In this region, most rain fell in June–October. March–May was the dry season, and November–February a period of cooler northerly winds and lower rainfall. In each environment, monthly growth of 39 adult plants was tracked for a year. [Cervera et al. 2007, p. 621–623]
Growth was determined by the number of new areoles above marked spines in the apical stem region. This separated production of new structures from hydration-related changes in stem dimensions. The mass of new growth was estimated from areole counts and a calibration of the relationship between plant dimensions and dry mass. [Cervera et al. 2007, p. 622–623, ryc. 1]
Nocturnal CO₂ uptake and drought
Gas exchange was studied in four adult plants from each site in three seasons. In the rainy season, about 97% of the daily net CO₂ balance occurred at night and about 3% early in the day. Daily balance was 17.6 ± 0.27 mmol CO₂/m² in the forest and 18.8 ± 0.31 mmol CO₂/m² on the dunes. This rhythm corresponded to CAM metabolism, with nocturnal carbon dioxide uptake. [Cervera et al. 2007, p. 623–625, ryc. 4–5]
After thirty days without rain, the daily net balance fell to 1.35 ± 0.08 mmol CO₂/m². Soil water potential at 15 cm depth was then about −19.8 MPa in the forest and −22.4 MPa on the dunes. Stomatal opening shifted towards midnight, and morning CO₂ uptake contributed about 13% of the daily balance. External carbon uptake thus continued on a small scale despite the absence of new areoles during the dry season. [Cervera et al. 2007, p. 623–626, ryc. 3–5]
Light and adult plant growth
The greatest adult plant growth was associated with microhabitats receiving 60–80% of the daily total of photosynthetically active radiation measured above local vegetation. Above 80%, growth declined. The percentage referred to a simultaneous local measurement, and the study compared natural microhabitats. [Cervera et al. 2007, p. 624–626, ryc. 7–8]
Light and water limited plant activity in different parts of the year. The relationship between growth and illumination was assessed in adult specimens. Drought inhibited new areole formation even while small-scale gas exchange continued. Both relationships describe seasonal growth in the Yucatán populations studied. [Cervera et al. 2007, p. 624–627]
Related articles
Materials from the author's archive
The species also appears in Konrad Szychowski's private material archive. [Cactáceas y Suculentas Mexicanas 1959, file p. 17] [U.S. Fish and Wildlife Service 2003, file p. 13]
Synonyms and names in the literature
Mammillaria gaumeri · Neomammillaria gaumeri · Mammillaria heyderi subsp. gaumeri · Cactus heyderi · Neomammillaria heyderi [2-WWW]