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Coryphantha scheeri var. robustispina is a small globular cactus 10-18 cm tall with distinctive, straw-colored central spines (ca 2 cm long on mature plants). Radial spines number 6. Plants have prominent tubercules, the tip of each having an aeroele. The tubercules have a central dorsal groove. Young aereoles are densely covered with wool, old ones are completely smooth. Older tubercules toward the bottom of plants can differentiate to form new plants. Flowers are pale yellow, about 4 cm across, with fruits green elliptical and juicy at maturity. Plants flower in early July. Seeds are brownish and relatively large, to 2 mm. Plants were first collected in 1856 by Schott in the Baboquivari Mountains in Sonora, Mexico. In 1856, it was published by Engelman as Mamillaria robustispina, based on the large seed size, and Kuntze (1891) then published it as Cactus robustispinus. Britton and Rose renamed it as Coryphantha robustispina in 1923, and in 1953, it was designated as a variety of Coryphantha mulenpfordtii, by Marshall. Finally, Lyman Benson split C. scheeri into 3 varieties, one of them being var. robustispina.
Plants are found on alluvial hillsides in rocky, sandy soils in southeastern Arizona. Plants are common nowhere within their range, and are rather difficult to locate. The habitat type is primarily desert grassland at elevations ranging from 2,300 ft. to 5,000 ft. Populations and population numbers are trending downward rather drastically, due to loss of habitat. Urban development is the primary threat. Additional impacts include road construction, agriculture, mining, off-road vehicle use, grazing, and introduction of non-native grasses. Plants are designated Threatened under the Endangered Species Act (1990), and are designated as Forest Service Sensitive, and Highly Safeguarded by Arizona state law. Additionally, the variety is listed in CITES in Appendix
In 1981, seven populations were monitored by Art and Barb Phillips. They believed that although the populations themselves were biologically stable, the threats posed by urbanization and mining placed a number of these populations in imminent danger. Even salvage efforts were not conducted properly, as plants were misidentified as young Ferocactus as they were collected. Approximately 25 populations are known from the U.S southwest, and more occurrences are known from Mexico.
Desert Botanical Garden salvaged approximately 75 plants clones from a proposed site in a Green Valley housing development. Available fruits and seeds were salvaged at the same time. Since 1993, the Garden has produced approximately 300 seeds in cultivation through controlled cross-pollination. A germination test was conducted on field-collected seeds from the original collection, yielding a percentage of 35%. Tests were conducted in the greenhouse, with temperatures ranging from 70-100 F, using Steve Brack's "box" method, whereby pots are placed in a plywood box covered with window screen and misted twice daily. Plants in greenhouse cultivation are repeatedly infested with spidermites, and must be grown outdoors with some protection from the west sun. Plants were translocated from the ground to pots during a construction project in May 2000. As of December 2000, no casualties have been observed. The DBG has seeds and plants from five populations in southern Arizona.
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