C. B. Wolf (pro sp.). 1938. Occasional Papers of the Rancho Santa Ana Botanic Garden 1: 79.
Cylindropuntia fosbergii is a narrowly-endemic cholla that occurs on flats and hillsides in a very limited area of eastern San Diego County, California within the southern half of Anza-Borrego Desert State Park. C. fosbergii is tree-like and grows to 3 m tall. The stems are very easily-detatched. The joints are 4 to 18 cm long by 2 to 5.5 cm wide with dense pinkish spines. This, plus its overall resemblance to C. bigelovii gives it the common name “pink teddy bear cholla”. The flowers are pink to bronze with green filaments. The fruits are dry to leathery and generally sterile. C. fosbergii is triploid (2n = 33), hence its dependence on clonal reproduction. It is possible that, like C. bigelovii, it produces occasional diploid individuals, but this has not yet been shown.
C. fosbergii has been described as a hybrid between C. bigelovii and C. echinocarpa, but neither morphological nor genetic studies support that hypothesis. Mayer et al. (2011) attempted to determine the parentage of C. fosbergii. None of the Cylindropuntia included in that study, other than C. bigelovii, appeared to be closely related to C. fosbergii. It is possible that C. fosbergii resulted from an ancient hybridization event with a now-extinct parent species or perhaps a Baja species such as C. alcahes that may have had a more widespread distribution in the past. Until further information is uncovered regarding C. fosbergii‘s possible hybrid origin, the Jepson Manual authors have decided to treat it as a good species in its own right.
C. fosbergii is included in the California Native Plant Society Rare Plant Inventory as a List 1B.3 (rare, threatened, or endangered in California and elsewhere; not very endangered in California). Although it has a very narrow range, the entire range is within Anza-Borrego Desert State Park.
Tom Chester’s Plants of Southern California website provides an expansive article about C. fosbergii and other southern California Cylindropuntia. C. fosbergii has previously been known as Opuntia bigelovii var. hoffmannii, but this name is invalid.