Newly Described Cacti from Baja California

After years of research, miles of field work, and countless hours poring over herbarium specimens and scientific publications, Curator of Botany Jon Rebman, Ph.D., has discovered seven cacti that are new to science. These newly named species, just published in the scientific journal Madroño: A Western American Journal of Botany, include six chollas and one species of prickly-pear, all endemic to the Baja California region.

In the January 2015 issue of Madroño, Rebman describes each species for the first time and provides details on distribution, associated vegetation, rarity, other related species, botanical illustrations, and identification keys. The six chollas include: Cylindropuntia alcahes var. gigantensis Rebman; C. alcahes var. mcgillii Rebman; C. cedrosensis Rebman; Cylindropuntia ganderi var. catavinensis Rebman; Cylindropuntia libertadensis Rebman; and C. waltoniorum Rebman; and the prickly-pear is Opuntia clarkiorum Rebman.

As Curator and Mary & Dallas Clark Endowed Chair of Botany, Rebman spends much of his time identifying, classifying, naming, and describing plants from our focus region of southern California and Baja California. Some of the new cacti that Rebman just described required extensive measurements of various morphological traits in order to tease apart the new taxa from previously known species.

However, sometimes finding new species is considerably easier if the new entity is from an unexplored area and looks very different than other related taxa in the region. One such example is the newly named Cylindropuntia libertadensis. In a previous issue of Field Notes, we had a story about natural history exploration in the little-known Sierra de La Libertad in the central part of the peninsula. During one of the first expeditions to this Sierra, Rebman hiked for about three days in a long canyon called El Paraíso, which is where he first encountered the new species that he would later name after the Sierra de La Libertad. Rebman noticed there was a cholla scattered all along the canyon bottom that resembled another more common cholla in the area, but had a very different growth habit, flower color, and fruit type. After a few days of field examination, Rebman was convinced that it was a plant entirely new to science. In fact, this newly described species is quite rare because it has only been seen within the confines of El Paraíso Canyon for a distance of approximately 16 kilometers, although it is quite abundant there. In general appearance, this new cholla is very similar to Cylindropuntia cholla and even grows in mixed populations with it at times. However, different flower color along with differences in stem characters easily separate these two related species. Further investigation is still warranted to obtain more detailed information about C. libertadensis.

Another new cholla described is Cylindropuntia cedrosensis which occurs on both Cedros and West San Benitos islands off the central Baja California peninsula. This is a distinctive new species, but the flowers and chromosome number are not yet known. Although it has a general appearance similar to the Coast Cholla (Cylindropuntia prolifera) found commonly in coastal San Diego, the fruits are spiny and strongly depressed, and thus it probably is not too closely related.   

Further investigation is needed in order to obtain more detailed information about C. cedrosensis. This cholla species relies quite heavily on vegetative propagation as the stem segments dislodge very easily. The spines of the stems are strongly barbed and easily attach to passersby for dispersal. On West San Benitos Island, this new species is responsible for killing various pelagic bird species such as Cassin’s Auklet and storm-petrels. According to ornithologist Phil Unitt, during fieldwork on this island in 1974, he vividly remembers extracting many bird skeletons from the chollas there in order to make specimen collections and even states that “this cholla must be a major control on the numbers of burrow-nesting seabirds that use the island.”

Two of the new cactus species were named in honor of long-standing patrons of the Museum. One new cholla was called Cylindropuntia waltoniorum (common name: Walton’s Cholla) in honor of John and Christy Walton for their support of research, conservation, and education on the Baja California peninsula and in the Gulf of California. Also a new prickly-pear cactus was called Opuntia clarkiorum (common name: Clarks’ Prickly-pear), named in honor of Mary and Dallas Clark for their long term support of natural history research in the southern California and Baja California regions.

Stay tuned for more research findings on our blog from the talented scientists here at the San Diego Natural History Museum

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