Plant Species of the Borrego Desert:
Distribution of Cylindropuntia echinocarpa and C. ganderi in the Borrego Valley Area
Distribution of Cylindropuntia echinocarpa and C. ganderi in the Borrego Valley Area
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| Fig. 1.
Left: Two pictures of the same plant of C. ganderi, Gander's cholla, taken from the south (top) and west (bottom), showing how different the color, and even some of the overall gestalt, of the plant appears from different viewpoints. Right: Pictures of two different plants of C. echinocarpa, both taken from the south. The top one has golden spines, with the common name golden cholla; the bottom one has white spines, with the common name silver cholla. Both plants are the same species. All three plants are found within 100 feet of each other just south of Christmas Circle in Borrego Springs, and were measured in detail and analyzed with a PCA to verify their species determination. These plants show some of the typical differences between these species that allows them to be recognized at a glance. C. ganderi is mostly greenish, at least from some viewing angles; it has many stems from the base; its branches are ascending; and its ultimate segments are long, mostly pointing to the sky. C. echinocarpa is silvery or golden; it has few stems from the base; its branches are often spreading; and its ultimate segments are short, mostly not pointing to the sky. See also Don Rideout's pix showing both species together just north of Christmas Circle. Click on the pictures for larger versions. | |
This page shows the geographic and elevational distribution of Cylindropuntia echinocarpa and C. ganderi in the Borrego Valley Area. It does not discuss how to distinguish the two species, although Fig. 1 shows some of the characteristics that typically distinguish them at a glance. I'll eventually write a separate page with more information on how to distinguish these two species. Until then, in addition to the discriminants mentioned briefly in Fig. 1, see Pictorial Identification Guide and Analysis of How Well Non-Blooming Specimens Are Distinguished, pages that I wrote many years ago (in 2007) when I was first studying our cholla species.
I've long been interested in the distribution of our cholla species, so over the years have taken a number of GPS points of these two species with the intent of making maps like the ones shown in this page. I've now augmented my points with iNaturalist observations, and vouchers with good locations. I've tossed all iNat observations that had a stated accuracy of more than 100 m, and any voucher with only a vague location like "Borrego Desert".
I've reviewed the iNat observations for C. echinocarpa for all locations that seemed questionable based on my data. Most of those were actually observations of C. ganderi, and I've added my determination to those individual observations online, removing them from their original determination of C. echinocarpa. For some of them, there wasn't enough information in the pictures to determine them, so I've removed them from the maps and graphs below. I plan to follow up four of them in the field to get their determinations.
Three vouchers of C. echinocarpa were removed from the maps and graphs since there are no C. echinocarpa plants at the locations of those vouchers. Those vouchers are either misdetermined or their localities are incorrect. Two of those vouchers are quite far from any actual C. echinocarpa location (and one of those was taken by Lyman Benson, the expert on the Cacti of California!). The third one of those vouchers is within a few miles of C. echinocarpa plants. That voucher actually has both determinations on its sheet, possibly indicating it is a hybrid between the two species, or simply demonstrating how difficult it is sometimes to discriminate between these two species in a voucher made from a small part of a plant. There is in fact a single hybrid plant at or near the location of that voucher, as verified from a Principal Components Analysis, so the voucher could well be of that plant. I also revised the georeferenced coordinates of a fourth voucher to fit its locality.
Fig. 2 shows the distribution of the two species in the Borrego Valley area on a Google Earth map showing the terrain.
Fig. 2. Geographic distribution of C. echinocarpa (magenta filled circles) and C. ganderi (blue filled circles) in the Borrego Valley Area. The symbols for C. ganderi were intentionally made smaller to better show the overlap area of the two species.
It can be seen from Fig. 2 that C. echinocarpa is confined to the desert floor, including the Borrego Badlands. C. ganderi is mostly found on the mountain slopes above the desert floor, but is sometimes found on the immediately-adjacent desert floor, where it can sometimes overlap with C. echinocarpa.
The separation of the two species is probably a function of available moisture. Above the desert floor, there is more rainfall, and summer temperatures are lower, suiting C. ganderi. This is not strictly a function of elevation, as shown by the C. ganderi plants living in the extreme northeast corner of San Diego County, at the very low elevations near that part of the Salton Sea. The extreme northeast corner of San Diego County is actually a quite mesic location, with a number of other species normally found at much higher elevation on the west side of Borrego Springs; see the Flora of Extreme Northeast San Diego County.
Both S22 and SR78 were surveyed for these two species all the way to SR86 near the Salton Sea, but no specimens were found east of those shown on the map. There is a lone voucher of one plant of C. echinocarpa near the junction of S22 and SR86. Due to the lower elevations closer to the Salton Sea, the annual rainfall decreases, and the summer temperatures increase, making conditions too inhospitable even for C. echinocarpa.
The subsequent maps and plots on this page are for latitudes above 33.20° in order to show how the two species separate by elevation on the west side of Borrego Springs, and the south side of the Santa Rosa Mountains. The plots were made using 521 locations for C. echinocarpa, and 1,120 locations for C. ganderi. The number of locations from each source are given in Table 1 at the bottom of this page.
A plot of the elevation vs. longitude is shown in Fig. 3 for C. ganderi, and in Fig. 4 for C. echinocarpa. The elevations were derived from the geographic coordinates by using the USGS Elevation Retrieval.
Fig. 3. Plot of elevation vs. longitude for C. ganderi for latitudes above 33.2° in the Borrego Valley area from my data (labeled "TJC") and iNaturalist data (labeled "iNat"). Top: All elevations. Bottom: only elevations below 1400 feet to match the plot of C. echinocarpa in Fig. 4.
The group of points below an elevation of 400 feet are from the extreme northeast corner of San Diego County, on the north side of the Santa Rosa Mountains.
I have not reviewed the iNat data for C. ganderi, and hence some of those might be misdetermined C. echinocarpa. Voucher locations were not included since there were only a small number in this area.
C. ganderi inhabits essentially the entire Desert Transition Zone in this area, from 4200 feet elevation at the top of the Montezuma Grade near Ranchita, all the way to 800 feet elevation at the junction of S22 with Palm Canyon Drive in Borrego Springs.
Fig. 4. Plot of elevation vs. longitude for C. echinocarpa for latitudes above 33.2° in the Borrego Valley area. Different symbols are used for each data source; I have reviewed all iNat observations whose locations seemed questionable. The symbol for vouchers was made larger to make them stand out (note some in the middle of the plot are still almost hidden behind other symbols).
On the west side of Borrego Springs, on the left of this plot, C. echinocarpa locations are all below 850 feet elevation, with most below 800 feet. In the Borrego Badlands area, in the middle of this plot, locations reach up to 1250 feet.
Fig. 4 shows that on the western side of Borrego Springs, on the left of that plot, C. echinocarpa is mostly found below 800 feet elevation, with the highest known specimen at an elevation of 850 feet. Farther to the east, in the drier Borrego Badlands and Borrego Mountain areas in the middle of the plot, it can be found as high as 1250 feet elevation. Yet farther to the east, in Imperial County, on the right of the plot, it drops out below roughly 400 feet, where conditions become too dry and hot for it.
Fig. 5 plots both species together for my data, for an easier comparison of the values for both species except in some of the areas where they overlap.
Fig. 5. Plot of elevation vs. longitude for C. echinocarpa and C. ganderi. Different symbols are used for each data source.
Fig. 6 zooms in on the western side of Borrego Springs, and shows the 800 foot elevation contour in that area as a reference line.
Fig. 6. Map of the geographic distribution of C. echinocarpa and C. ganderi on the western side of Borrego Springs, along with the 800 foot elevation contour. The boundary between the two species is very close to the 800 foot contour on the south, in the Hellhole Canyon area. The highest-elevation C. echinocarpa is found at slightly higher elevations in the Borrego Palm Canyon Area in the middle, and at slightly lower elevations in the Henderson Canyon area on the north.
I did detailed mapping in the Borrego Palm Canyon area on 24 December 2019. Most of the time, it is obvious at a glance whether a given specimen is C. ganderi or C. echinocarpa. However, at both the beginning and the end of my survey, in roughly the same geographic area, there were specimens that I could not determine at a glance, and still wasn't sure of the determination up close; see Fig. 7. I also found similar specimens in a short survey on 6 December 2019. Those specimens could be hybrids between the two species, especially since they are found only in the area where both species are found. It should be possible to discriminate hybrids through a PCA using detailed measurements, which I plan on doing in the future.
There could well be hybrids in the other locations where the two species are both found. The Jepson Manual treatment for Cylindropuntia says "hybridization common".
Fig. 7. Map of the geographic distribution of C. echinocarpa and C. ganderi in the Borrego Palm Canyon area, along with the 800 foot elevation contour. The locations of possible hybrid specimens are shown.
Table 1 gives the number of points for each species from each source.
Table 1. Number of GPS points for C. echinocarpa and C. ganderi by Source for the Borrego Valley Area north of Latitude 33.2°.
| Species | TJC | iNat | Vouchers |
|---|---|---|---|
| C. echinocarpa | 337 | 169 | 15 |
| C. ganderi | 756 | 346 | 18 |
Voucher data provided by the participants of the Consortium of California Herbaria (ucjeps.berkeley.edu/consortium/)
I thank Jane Strong for comments that improved the presentation of this webpage.