Plant Species of the Borrego Desert:
Cylindropuntia ramosissima, diamond or pencil cholla
Cylindropuntia ramosissima, diamond or pencil cholla
Table of Contents
Introduction
Species Description
Geographic Distribution and Habitat
Elevational Distribution
Density of Plants
Abundance
Comparison with Similar Species
Additional Photographs
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| Fig. 1. Two of the many forms of Cylindropuntia ramosissima, diamond or pencil cholla, a green / white almost-spherical form (top) and a golden wide erect plant (bottom). See Fig. 11 for additional forms. Numerous additional photographs are linked at the bottom of the Introduction.
Click on the photos for larger versions. |
Introduction
Most everyone loves Cylindropuntia ramosissima, diamond or pencil cholla, since it is a "cactus cutie", with pencil-thin stems and long spines that are usually one to a tubercle, which makes it easy to identify in our area. It is the only one of our cactus species that has such narrow stems, so the name "pencil cholla" is unique to it in our area. However, it has relatives with pencil-thin stems who live elsewhere, and also have "pencil cholla" as part of their common name, so some prefer to call our species diamond cholla (from the usual shape of the tubercles at the base of the spines). That doesn't completely solve the common name problem, since at least one other species has "diamond cholla" in its name, too. Other common names in use are branched cholla (since it is many branched, hence the scientific name of ramosissima), and branched pencil cholla.
The unique features of this species in our area are:
- its stem width is less than 1 cm (0.4 inches), compared to at least 1.5 cm (0.6 inches) for all other chollas;
- its tubercles are almost flat, less than 1 mm high;
- the tubercles usually have just a single long spine;
- the spine is longer than in any other cholla, up to 6 cm (2.4 inches), nearly twice the longest spine of other chollas of 3.5 cm (1.4 inches);
- it has the smallest flower of any of our cholla species, only about 2.5 cm (one inch) across, about the diameter of a quarter coin. It is tied with Mammillaria dioica for the smallest flower of any of our cactus species. See a visual comparison of the flower widths of our Cactus species in the Borrego Desert, which also has a discussion of errors in some sources for the size of its flower.
This species is quite variable in appearance. Munz 1974 says it is "variable as to color, statute and spininess". Some of its many forms are shown in Fig. 1 and Fig. 11.
Surprisingly, few people get to see blooms on this species! It typically blooms in the summer, when most people are not in the desert; the flowers are not open all day; AND it (perhaps) does not bloom every year. That's a lot of hurdles to surmount to find an open flower!
Jaeger (Desert Wildflowers, p. 158) writes "The flowers are small and occur infrequently; they are seldom noticed and many botanists confess they have never seen one." Morhardt and Morhardt write "small orange-brown to pinkish flowers appear about June in rare years, so you have to get out of your air-conditioned car to appreciate them". Turner et al, from their extensive fieldwork, say it blooms in April and May.
This species seems to bloom more frequently than is reported in the above sources. Blooms have been observed in our area in at least five of the last six years, in 2015, 2016, 2017, 2019, and 2020, from iNat observations and from Fred Melgert and Carla Hoegen's website. 2018 was a very dry year, so it perhaps did not bloom that year.
iNat observations of this species in bloom in our area range from 16 April to 27 June, from 11:52 a.m. to 7:24 p.m., within the April to August flowering time given in the Jepson eFlora. The time the flowers are open during the day is a longer interval than the "few hours from noon to 2 p.m." given in Bowers and Bowers, in Cactus of Arizona Field Guide, p. 183, but it is possible that noon to 2 p.m. is the most reliable time to catch an open bloom.
Bill Sullivan gives the following tip if you want to observe its blooms: "The best strategy would seem to be to stake out an area where the plants grow. In early May, start visiting it regularly, perhaps as often as once a week, looking for signs of buds."
The narrow stems pose a problem for this species, compared to other cacti, since their low ratio of volume to surface area isn't such a good idea for a desert plant that needs to minimize water loss. C. ramosissima solves that problem in two ways. First, it has much deeper roots than our other cactus species, to 5 feet (1.5 m) below the soil surface, to gather enough water to make up for the narrow stems (Environmental Biology of Agaves and Cacti, Park S. Nobel, 1988, p. 86). Most Sonoran Desert cacti have roots no deeper than 6 to 12 inches (15 to 30 cm) below the soil surface (Cannon 1911, in Dubrosvsky and North 2002, p. 49) Second, it lives in areas that can reliably supply at least infrequent water to its deep roots.
As a result, C. ramosissima has a very different distribution from our other cholla species. Its favorite habitat here is older deeper alluvium next to our mountain ranges. The runoff from the mountains supplies the alluvium next to the mountains with significantly-more water than is received on the open desert floor from rainfall alone.
This habitat allows helps the plants survive multi-year droughts, with at least some mountain runoff even in dry years, analogous to roadside plants getting extra runoff from the road surface. The deeper alluvium also probably stores water from wetter years that the plants may be able to use in drier years.
This habitat might be at least one reason the recent death rate for plants of this species is much lower than has been observed for C. bigelovii.
C. ramosissima might also live longer than other chollas, since many plants are found growing in a circle, with no plants in the middle of the circle; see Fig. 11. The circle might result from rooting of horizontal stems that touch the ground, or vegetative reproduction from stem segments that fall on the ground around a mother plant.
For many good photographs of this species in the ABDSP region, see:
- Fred Melgert's and Carla Hoegen's Anza-Borrego Desert Wildflowers: C. ramosissima. (27 photos as of 2 January 2021)
- iNaturalist observations of C. ramosissima in the ABDSP region. (345 observations as of 2 January 2021)
Species Description
Geographic and Elevational Distribution, and Habitat
C. ramosissima lives in the desert regions of the Southwest and northwestern Mexico, including Baja California. The vast majority of its population lives in a parallelogram 500 miles (800 km) north-south and 250 miles (400 km) east-west, with a few outliers beyond that area; see Fig. 2.
Fig. 2. The SEINet geographic distribution map of C. ramosissima as of 2 January 2021. See also the latest SEINet map.
The western edge of the range of C. ramosissima is where the edge of the Sonoran Desert in San Diego County meets the mountains. What causes the other edges of its range are less clear, but may be determined by competition from similar species. Turner, Bowers and Burgess 2005 comment that "Its rather abrupt eastern limit is not determined by any geographical feature. The elevational profiles strongly suggest that interactions at the arid limit of C. leptocaulis [desert Christmas cactus] have determined the eastern boundary. Interactions with C. tesajo [Baja pencil cholla] may shape the peninsular limit" (p. 301).
The geographic distribution presented here for the ABDSP area (as of 25 January 2021) has been compiled from 3,345 records with good locations from survey locations by Walt Fidler; survey locations by Tom Chester and companions; iNat observations; vouchers; and Calflora records. The iNat observations, voucher locations, and Calflora locations were reviewed to eliminate potential misdeterminations and poor locations.
The accepted locations are from:
- 2,415 GPS points from extensive surveys by Walt Fidler in the Sweeney Pass / Volcanic Hills Area. See Figs. 7 and 8.
- 552 GPS points from surveys by Tom Chester and colleagues, including points from five dedicated censuses for it where the plants were counted and GPS points were taken every 30 feet or so. See, for example, the survey along the southeast base of Coyote Mountain on 30 December 2020 shown in Fig. 6.
- 345 accepted iNat observations with good locations, including 79 from Terry Hunefeld; 65 from Fred Melgert and Carla Hoegen; and 48 from Don Rideout. 65 iNat observations were rejected; 39 had positional uncertainties of more than 100 m or had obscured coordinates; 22 were of planted specimens at the ABDSP Visitor Center; 3 had erroneous locations; and 1 was probably a planted specimen on a residential lot with what looked like other planted specimens.
- 18 accepted vouchers with fairly accurate locations, six collected by Larry Hendrickson and colleagues, four collected by Bill Sullivan, with the rest from seven other collectors.
- 15 records at Calflora, mostly contributed by Keir Morse.
Fig. 3 shows the known locations of C. ramosissima in our area from those 3,345 records.
Fig. 3. The geographic distribution of C. ramosissima in our area, with known accurate locations marked with pink / magenta dots. Most areas with a dense numbers of dots are ones in which dedicated surveys have been made. Some of those areas had just a few known points before, so it is quite possible some of the areas with sparse dots also have large numbers of so-far-unrecorded plants.
Also see enlarged versions for Borrego Valley, the Vallecito / Agua Caliente area, and the Sweeney Pass / Volcanic Hills Area.
iNat observations contributed most of the points away from the detailed surveys by Walt Fidler, and Tom Chester and colleagues, so you can click on the "Map" tab at upper left for iNaturalist observations of C. ramosissima to view the distribution of the iNat locations at any scale you would like (note that this will include locations that I've rejected in the maps on this page).
The preferred habitat of C. ramosissima can be mostly clearly seen by examining its distribution in Borrego Valley and Clark Valley, shown in Figs. 4 and 5.
Fig. 4. The geographic distribution of C. ramosissima in the Borrego Valley. Note that nearly all its locations are on darker-colored ground, which is from older alluvial surfaces (possibly from increased amounts of desert varnish). Most of those locations are in deeper alluvium next to mountains.
Fig. 5. The geographic distribution of C. ramosissima in the Clark Valley / Coyote Mountain / Borrego Badlands area; click on the map to get a slightly larger version.
Mike Crouse, Joe Woods, and I surveyed along the southwest base of Coyote Mountain, and found no plants of this species until we encountered a large alluvial fan, circled at middle left above, with the alluvial fan seen more clearly in this zoomed map.
It is quite stunning that this species refuses to live in washes with lighter-colored sand, or even to dip its toes into more recent alluvium when it is adjacent to older alluvium where it is abundant! The lighter-colored sand in those washes may simply be sand kept freer of desert varnish by more-recent wash flows.
There have been a number of surveys in Clark Valley proper, the Coyote Creek washes, San Felipe Creek proper, etc., without finding essentially any plants of C. ramosissima in those areas. In contrast, plants of C. echinocarpa are found over a much wider area of the desert floor; see its iNat map.
See also these maps showing where C. ramosissima was, and was not, found in the southern Borrego Springs Area:
- 21 January 2021 survey route shown in green, with blue diamonds showing C. ramosissima locations found in that survey as well as nearby iNat observations;
- C. ramosissima locations on Google Earth satellite image with boundaries shown between different colors of alluvium (same image without boundaries)
The western boundary of C. ramosissima in the maps linked above is probably where it becomes too mesic for C. ramosissima. That boundary also roughly corresponds to where C. echinocarpa is replaced by C. ganderi to the west.
Because this habitat of alluvial fans at the base of our mountains is not frequently visited by botanists or iNat observers, C. ramosissima is likely to have many more locations than are shown in the above maps. As an example, Fig. 6 shows what the known C. ramosissima distribution at the southeast base of Coyote Mountain looked like before, and after, my 30 December 2020 survey.
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| Fig. 6. Distribution of C. ramosissima at the southeast base of Coyote Mountain from before my 30 December 2020 survey (left; locations shown by green markers) and after (right; locations shown with pink/magenta dots). | |
Prior to my survey, I was quite curious as to whether C. ramosissima would be found only in a few locations along the southeast base of Coyote Mountain, or would be more widespread. I was quite surprised at how widespread it was along my survey route, and how numerous it was. I counted 786 plants along my route.
Birgit Knorr reports that C. ramosissima is also abundant in the older alluvium between Vallecito Wash and the Carrizo Badlands, despite there being very few locations recorded in that area, which is the upper right half in the Vallecito / Agua Caliente Area map.
The most complete map showing the density and habitat of C. ramosissima is from the surveys by Walt Fidler of the Sweeney Pass / Volcanic Hills area. Walt did an extraordinary seven day census of the plants there in January 2021, counting a total of 11,131 plants, represented by 2,415 GPS points. His GPS points, along with a few other locations from iNat, are all shown in Fig. 7.
Fig. 7. Map of C. ramosissima locations in the Sweeney Pass / Volcanic Hills Area, from 2,415 GPS points taken by Walt Fidler, and 12 iNat locations.
Walt increased the density of GPS points in this area by a factor of 200!
The density of Walt's survey allows one to zoom into the map using Google Earth to see precisely the habitat of C. ramosissima in this area. Fig. 8 shown an oblique aerial view of the locations, looking east from 325 feet above the ground surface.
Fig. 8. An oblique aerial view of part of the Sweeney Pass / Volcanic Hills Area, showing locations of C. ramosissima GPS'd by Walt Fidler. The aerial view is looking east from 325 feet above the ground surface. Click on the figure for a map showing a larger area.
Note that once again, there are few locations in the main wash seen in the middle of this terrain view. Most of the plants are found in the smaller tributary washes that presumably have less scouring. Even in those smaller tributary washes, the plants are often found at the edges of those washes.
In this area, there are few plants on the terrain between the washes, since that terrain is mostly desert pavement. Walt reported he noted this pattern ubiquitously: "Wash with pencil cholla, desert pavement with none; another wash with pencil cholla, desert pavement with none; over & over again."
Elevational Distribution
The elevation distribution of C. ramosissima is shown in Fig. 9, where it is plotted versus longitude.
Fig. 9. Plot of elevation vs. longitude, with the source of the location points given.
The vast majority of plants in our area are found at 500 to 1500 feet elevation, with some plants found close to sea level, and, surprisingly, four stragglers from 1876 to 2568 feet! The highest-elevation plant is on the top of Travelers Peak at 2568 feet. Three of the four highest-elevation plants are posted at iNat by Fred Melgert and Carla Hoegen: 2568 feet at Travelers Peak; 2053 feet in Smoke Tree Canyon; and 1876 feet on Coyote Mountain. (The elevations are from the highly-accurate USGS National Map.)
Density of Plants
Density measurements, in descending order:
- 377 plants per mile in the Sweeney Pass / Volcanic Hills Area. On 21 January 2021, Walt Fidler counted 3,318 plants in a total unique survey distance of 8.8 miles, a density of 377 plants per mile; see Figs. 7 and 8.
- 230 plants per mile at the southeast base of Coyote Mountain, from my count of 359 plants in 1.56 miles; see Fig. 6.
- 225 plants per mile in the alluvial fan east of Palo Verde Wash halfway to Smoke Tree Wash, from my count of 259 plants in 1.15 miles. The peak was 240 plants per mile over a subset of that distance. Other counts in that area were 240, 215 (both subsets of the 225 plants per mile), 165, 138, and 28 plants per mile; see map.
- 195 plants per mile in the alluvial fan northeast of Lute Ridge, from my counts of 454 plants in 2.33 miles. Other densities in that area were 125 and 36 plants per mile. See map.
- 138 plants per mile in 0.32 miles near the 90° bend of Borrego Springs Road in the southern part of the town of Borrego Springs; see middle left part of this map.
- 123 plants per mile in 1.95 miles near the mountains north of Vallecito Wash and east of Vallecito County Park.
- 116 plants per mile along 0.69 miles near Yaqui Pass Road near the top of the alluvial fan south of Borrego Springs, count by Don Rideout.
- 38 plants per mile in 0.47 miles below Yaqui Meadows and above Borrego Springs Road; see southern part of this map.
Abundance
Because of the lack of surveys in its typical habitat, the area occupied by C. ramosissima is uncertain. At minimum, adding up the area of polygons that enclose the known large populations, C. ramosissima occupies a total area of about 70 square miles. Given the uncertainties, it probably occupies an area of about 100 square miles, which is about 10% of the total area of the Borrego Desert below 3000 feet elevation, which is roughly 1000 square miles.
C. ramosissima is probably a moderately-abundant shrub in the ABDSP, more abundant than a number of shrubs, but far less abundant than the most abundant species. I estimate there are at least 30,000 plants of this species here, which is two to three times more abundant than is Ericameria paniculata. Accounting for unsurveyed areas, there could be as many as 60,000 plants total. For comparison, our most abundant species, creosote and burroweed, have something like 10 to 100 million plants each here, and are therefore something like 200 to 3,000 times more abundant.
My abundance estimate comes from adding up estimated numbers in each area in which it is found. The following gives the estimated numbers for different areas, with areas with the highest abundance listed first:
- the base of the southeast Santa Rosa Mountains, from Lute Ridge to the Arroyo Salado, including Palo Verde Wash, Smoke Tree Wash, and the Truckhaven Rocks area. I counted a total of 1,050 plants in surveys on two different days between Lute Ridge and Smoke Tree Wash, with densities of 165 to 240 plants per mile in the higher density areas. By assuming the same density of plants is found in unsurveyed areas in the vicinity of those surveys, there would be 7,000 plants in the vicinity of those surveys. Areas to the east have many known locations, but without actual counts. The density of C. ramosissima plants in those areas is definitely less than in my surveyed areas, and the area inhabited by C. ramosissima is probably somewhat less there. My best guess is that there are perhaps 5,000 plants in those areas. The total in this entire area would then be something like 12,000 plants.
- Sweeney Pass / Volcanic Hills. Walt Fidler counted 11,131 plants in seven days of very complete surveys of the main population. My best estimate for the total number of plants would be 12,000 plants to account for unsurveyed areas there.
- the southeast Coyote Mountain area. I counted 786 plants in a survey of what is almost surely the largest population, with a density of 200 plants per mile on average. There is about seven times the coverage area inside my survey, so the best estimate of the total population is 5500 plants.
- the alluvial fan above Clark Well. There are a handful of iNat points in a route going up that fan, but no number of plants observed to make a reliable estimate. This fan could contain as many as 1,000 plants, but it might only contain dozens of plants.
- southern Borrego Springs / Yaqui Meadows / Yaqui Pass / Cactus Valley / Old Kane Springs Road area. Three counts were made in this area, all with somewhat-low densities of plants. I counted 117 plants in a three mile survey through the edge of the population just south of Borrego Springs township. Don Rideout counted 84 plants in a distance of 0.7 miles, for a density of 116 per mile. I counted 70 plants in a one mile survey in Cactus Valley. Extrapolating from those counts, I estimate there are perhaps 800 plants in this area. There could be significantly more if there are plants in the Cactus Garden and east to Lower Borrego Valley.
- Vallecito Creek / Aqua Caliente Area. I counted 241 plants in a two mile survey through the main population on the north side of Vallecito Creek. Extrapolating from that number is difficult, since the habitat is different in the Agua Caliente area. My best guess is 500 plants in this area.
The number of plants in Upper Clark Valley, the Borrego Badlands, and the Carrizo Badlands is probably low, but counts are needed to verify this.
Comparison with Similar Species
Young plants of C. ganderi and C. echinocarpa, and depauperate plants of those two species, are sometimes mistaken as this species, since the stems of young plants of those two species are slender, and the spination is often not fully developed. If you think you have a young plant of C. ramosissima, look around to see what adult chollas look like in that area. If you don't see any adult plants of C. ramosissima, it is highly likely your young plant is not that species.
Additional Photographs
A ring of purplish plants |
A plant in fruit |
A plant with laddered stems all facing south |
A tall and skinny plant |
| Fig. 11. Other forms of Cylindropuntia ramosissima. Click on the photos for larger versions. |
Voucher data provided by the participants of the Consortium of California Herbaria (ucjeps.berkeley.edu/consortium/) in early January 2021.