Plants of Southern California: Opuntia echinocarpa, O. ganderi, O. parryi, and O. wolfii: Pictorial Identification Guide
Pictorial Guide Showing How To Identify These Species
The western Sonoran Desert (w DSon) has a number of interesting endemic species, including three cholla species.
Most people have no trouble recognizing teddy-bear cholla, O. bigelovii, and pink teddy-bear cholla, the w DSon endemic O. fosbergii, which are easily distinguished by their overall form and the lack of spines on their fruit. Those teddy-bear chollas are discussed separately.
This page discusses four somewhat-similar chollas that are often confused with one another: Opuntia echinocarpa, O. ganderi, O. parryi, and O. wolfii.
Synonyms and type localities for these species are as follows:
Name used here Synonyms Type Locality O. echinocarpa O. echinocarpa var. echinocarpa
Mouth of Bill Williams River, Arizona O. ganderi O. acanthocarpa var. ganderi
O. acanthocarpa ssp. ganderi
Three miles below the old Vallecito Stage Station, San Diego County O. parryi O. parryi var. parryi
O. echinocarpa var. parkeri
Cylindropuntia californica var. parkeri
San Felipe (O.p.), Campo (O.e.p.); both in San Diego County O. wolfii O. echinocarpa var. wolfii
Mountain Springs Grade, sw Imperial County
Since two of these species, O. ganderi and O. wolfii are endemic to w DSon, and another, O. parryi, is endemic to w DSon plus adjacent inland areas, it seems surprising at first glance that more southern California botanists aren't familiar with how to distinguish these species.
But in actuality, there has been so much confusion over these species that there is no wonder that even excellent botanists throw up their hands when it comes to these species. There are at least three major sources of confusion:
O. ganderi was not keyed or described in the Jepson Manual. It was mentioned only as a "hybrid" under O. parryi, even though evidence for its hybrid nature was lacking. In fact, it is no longer thought to be a hybrid (Flora of North America; Rebman 2005).
Since O. ganderi is the most common cholla species on the desert side of the mountains in w DSon away from the desert floor, it creates massive confusion when botanists try to shoehorn its specimens into a different species.
Further confusing the matter, O. ganderi used to be a variety of O. acanthocarpa. When O. ganderi was deleted as an entry in the Jepson Manual, many botanists began labeling specimens of O. ganderi as the only variety of O. acanthocarpa given in the Jepson Manual, var. coloradensis. This taxon is only found along the Colorado River in very easternmost southern California, although it is possible that it makes an appearance at the extreme northeast edge of San Diego County near the Salton Sea.
The Munz (1974) and Benson (1969) key and description can often key O. ganderi properly, but because many specimens are close to the boundaries in the key between the taxa, the key occasionally results in specimens of O. ganderi being determined as O. echinocarpa or O. wolfii.
- O. parryi is not correctly described or keyed in Munz (1974), the Flora of North America, or in Benson (1969). All of these floras except the Jepson Manual key O. parryi under Fruit sparsely spiny, yet nearly all specimens of O. parryi (except those closest to the coastline or at highest elevations) have fruit that are medium to densely spiny. (I define few-spined fruit as having roughly 0-10 spines per fruit; moderately-spined fruit as having roughly 30-50 spines per fruit; and densely-spined fruit as having roughly over 100 spines per fruit.)
It is a little puzzling how this rumor of sparsely spiny fruit got started, since half of all Benson's specimens come from areas with moderately- to densely-spiny fruit, at least in early 2007. It is possible that the spines on the fruit easily fall off in pressed, dried plants; I'll check his vouchers in the future. Other possibilities are discussed here.
The Jepson Manual gives an overall excellent description of O. parryi, and correctly recognizes that the fruit is variably spiny. It keys O. parryi under both Fruit densely spiny and Fruit spineless, but farther along keys it under St gen < 2 cm diam, which is almost never the case.
As a result of these problems in the floras, specimens of O. parryi have sometimes been determined as "O. ganderi", "O. acanthocarpa var. coloradensis", and even "O. echinocarpa", and many specimens have been thought to be hybrids. See "Intergradation" between Opuntia parryi and O. ganderi.
Also, O. parryi is not present in the Jepson Desert Manual, since it just barely makes it into DSon. This makes it impossible to key out any specimen to O. parryi if you are using that flora.
- Although the vast majority of specimens of each taxa are clearly distinguishable from each other, some specimens of O. parryi and O. ganderi are very close to each other. Some voucher specimens, which are only a small portion of a typical specimen, are especially difficult to determine, since they lack clues present in the entire plant and its neighbors.
The confusion over these taxa is shown in these two examples:
- O. echinocarpa has a broad distribution throughout the entire Sonoran Desert, yet wasn't one of the 13 cholla species whose distribution is given in Turner, Bowers and Burgess 2005, perhaps due to the difficulty in distinguishing it from O. acanthocarpa and similar species.
- The difficulties in distinguishing these species probably also accounts for the absence of O. ganderi on the interpretative panel on the Anza-Borrego Desert State Park Visitor Center Nature Trail. This panel is titled Common Cacti, lists five other species of cacti, yet is surrounded by O. ganderi, the most common cactus there by far!
No one, especially myself, can fault any of the people, sources or examples above. Cacti are especially difficult to get right taxonomically, since botanists rarely study them or collect them, and many areas in southern California remain under-vouchered for cacti. In fact, the taxonomy of these species in the w DSon only regained some measure of clarity in 2001, when Rebman restored O. ganderi to its rightful place in the w DSon as a valid species.
I personally was quite confused about O. ganderi until I read an enlightening article by Jon Rebman, 2005, Gander's Cholla: Our Common But Barely Known Cactus, in the Anza-Borrego Desert Natural History Association's The Sand Paper, 34, Issue 2, p. 3. Jon then kindly spent with me some time clarifying the other species as well.
In early 2007, I began a project to determine the locations and properties of O. parryi and O. ganderi. This page is one of the results of this ongoing project.
This page shows where these species are found, especially in the desert portion of San Diego County, and how to tell the difference between them. For an overview of chollas in San Diego County, see Chollas.
Pictorial Guide Showing How To Identify These Species
All of these species have fruit which are moderately to densely spiny, in contrast to the spineless fruit of the teddy-bear cacti (O. bigelovii, O. fosbergii). You can almost always find fruit present on the plant somewhere, either at the tips of the stems or tangled amidst the spines below.
The following pictures show the densely-spiny fruit of each of these species, as well as a typical teddy-bear cacti fruit:
Spineless fruit of O. bigelovii / O. fosbergii
O. parryi O. ganderi
O. wolfii O. echinocarpa
As you can see from the very dried fruit above, you don't need fresh fruit to make this determination. These pictures were taken in January 2007; the fruit were at least six months old.
Don't expect to distinguish these four species based on their fruit; all you have to do is make sure there are spines on the fruit to rule out the teddy-bear chollas.
There are only two other cholla species in San Diego County that have spiny fruit. The first is O. acanthocarpa, which is rare and found only in the extreme northeast corner of the Anza-Borrego Desert State Park (Travertine Palms) where few people ever venture. The following assumes you are not in that area.
The second is the very different-looking pencil cholla, O. ramosissima. That species has stems literally only a pencil width wide, less than 1 cm (0.4 inch) in diameter.
The four species discussed on this page have stems at least 1.5 cm (0.6 inches) in width, two pencil widths, and usually much wider.
The following pictures shows typical stems of the four species near the stem tips:
O. parryi O. ganderi
O. wolfii O. echinocarpa
Note how easily O. parryi stands out. When you look at it, you see mostly the green of the stems largely unobscured by the spines. (The above picture is very typical of O. parryi but there are two populations of O. parryi with spinier stems: along the Santa Clara River in Los Angeles County, and some plants near Scissors Crossing along S2 in San Diego County. But even there the green of the stems is still quite noticeable.)
There is no need to even get close to the plants to see the difference in color. The following pictures show the appearance of the plants in the field in a distant view:
O. parryi O. ganderi
O. wolfii O. echinocarpa
In a view of the entire plant, for O. parryi you mostly seen the green of the stems, and the very noticeable tubercles (the elongated bumps along the stems). In contrast, for the other three species, it is the spines the draw your attention first, at least on the newest growth. Spines tend to become less prominent on older growth as age takes its toll on them. So don't be fooled if you see a lot of green on the other species below the upper portions of the branches.
All it takes to discriminate the remaining three species is attention to the branching habit of the plants.
O. ganderi has the vast majority of its new growth stems "reaching for the sky". Even if the lower stems of the plant become a bit tilted, as in the picture above, it sends out its new growth dead erect. This new growth is said to be strict, meaning that every branch is strictly parallel to each other. See two pictures by Wayne Armstrong of a field of O. ganderi that nicely illustrates this habit.
The following three pictures show some of the variability in the appearance in the field:
Note that not every stem is strict, and new growth often starts out at an ascending angle before turning to "reach for the sky". But if you look over the plant as a whole, you see a fair number of stem tips that are dead parallel and dead erect.
Note also the variability of the spines in the above pictures. Spines are simply too variable to reliably distinguish many cacti species.
O. wolfii is the hardest to discriminate from O. ganderi since its branches are strongly ascending and hence close to the erect branches of O. ganderi. But if you look at plants of O. wolfii, especially in a field of them, you won't see the tips of the branches "reaching for the sky" anywhere near as prominently. Nor will you see a large number of stem tips that are dead parallel and dead erect.
The following pictures show this difference in habit:
A baby O. bigelovii, with its single trunk and "branching mostly at its head habit", is on the right in the last picture above.
The difference in the branch angling is a bit subtle, but easily discernable once you've seen a number of specimens of each species.
The overall appearance of this species is also quite different from O. ganderi in a number of respects. The spines are denser, more uniform and whiter on O. ganderi, and less dense, often with 1-2 much longer spines, and more golden on O. wolfii.
If you have been successful in discriminating O. wolfii from O. ganderi, it is then a piece of cake to discriminate O. echinocarpa. O. echinocarpa has many branches that are spreading at right angles to its main stems, and often appears as a miniature tree with a single trunk.
The following pictures show how different O. echinocarpa looks for its branching angle:
Note how many branches are spreading at right angles in the above pictures, and try to find any similar branching in the above pictures for the other species.
The following table summarizes the differences given above, in the same order as above, which is a good way to go through the determination for a given specimen:
Species Distinguishing Characteristics O. parryi Green stems and tubercles very visible, spines generally not prominent O. ganderi Spines prominent on upper stems, hiding stems and tubercles; upper stems erect and parallel, "reaching for the sky" O. wolfii Spines prominent on upper stems, hiding stems and tubercles; upper stems ascending but mostly not parallel and erect O. echinocarpa Spines prominent on upper stems, hiding stems and tubercles; branches spreading, with many at right angles to main stems
See also the formal key for all cholla species in Anza-Borrego Desert State Park.
- Pictures and book learning are one thing, but there is nothing like seeing the plants themselves. Now that you know where the species are, and how to identify them, go take that trip along Highway S2 and see these species for yourself! (:-)
- If after seeing all these species, you find specimens that you cannot confidently classify to species, there are other differences between these species that you can check before you conclude that you are seeing hybrids:
- The flowers show the most striking differences, but most botanists rarely see flowers since the blooms occur only when the desert has already grown too hot for most people to venture there. However, if you are motivated enough to get the determination of your specimens, come back in April and May and check out the flowers.
- The lengths and widths of the stem segments, fruit and the tubercles distinguish these species. See Opuntia echinocarpa, O. ganderi, O. parryi, and O. wolfii: Analysis of How Well Non-Blooming Specimens Are Distinguished. Most of the specimens in the above photographs have been measured in detail as part of that analysis, which confirmed the species assignments given here. However, it requires patience to make detailed measurements of those, one risks close contacts with spines while making those measurements, and it requires detailed analysis in order to reliably separate some of these species.
- The characteristics of the spines, visible in close-up photographs, reliably separate all species except O. wolfii and O. echinocarpa, with the exception of two populations of O. parryi (see the following note). See the link immediately above for details and comparison photographs.
Some specimens of O. parryi appear spinier than the examples shown above, but are still usually easily distinguishable at a glance from O. ganderi. These specimens are infrequent, and hence weren't discussed above so as not to confuse the beginner. See Opuntia echinocarpa, O. ganderi, O. parryi, and O. wolfii: Analysis of How Well Non-Blooming Specimens Are Distinguished for pictures of those unusual specimens.
Two populations of O. parryi, one just south of Scissors Crossing and the other along the Santa Clara River in Los Angeles County, have spines close to O. ganderi, and must be distinguished based on other characteristics such as tubercle lengths and maximum stem segment lengths.
- Nearly all of the above has benefited from information from Jon Rebman; I thank him for kindly sharing his vast knowledge of these species. In particular, I first learned that O. ganderi was the most common of these four species from Jon, and that those specimens were not the "O. echinocarpa" that many botanists assumed them to be. I also first learned of the locations of the species along S2 from Jon, from personal communication, from his Sandpaper article, and from the article Desert in Bloom in the San Diego Natural History Museum Field Notes published in the regional edition of Natural History, April 2005.
- I thank Wayne Armstrong, Dave Stith, Norrie Robbins and Kate Shapiro for their help with field work on 23 January 2007 on my first trip along S2 to study these species. I also thank Norrie Robbins and Dave Stith for providing good scales in some of the above pictures. I thank Jane Strong for her usual helpful comments on this webpage.
Copyright © 2007 by Tom Chester
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
Comments and feedback: Tom Chester
Last update: 2 March 2007