Distinguishing Cylindropuntia bernardina, cane cholla, and C. ganderi, Gander's cholla
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| Fig. 1. Top: Cylindropuntia bernardina, cane cholla or valley cholla. Bottom: C. ganderi, Gander's cholla. Note the longer stem segments in this plant of C. bernardina, which makes the stems appear cane-like, the source of its common name of "cane" cholla. Both plants were growing in close proximity in Mason Valley, where the C. bernardina plant is an interloper right next to the road.
Such extreme differences only occur for about half of the population of each of these species. The other half of the time, differences will not be apparent to the eye for a single plant. It is therefore important to look at other nearby plants to make a solid determination. Click on the pictures for larger versions. |
This page is only on distinguishing Cylindropuntia bernardina (= C. californica parkeri = Opuntia parryi) and C. ganderi in areas where those are the only two cholla species that might be present. Those areas are typically in the upper desert transition zone, at elevations of 3000 to 4000 feet.
This page does not discuss two other similar chollas. C. echinocarpa is generally found only on or near the desert floor, at elevations of ~1000 feet and lower. C. wolfii is only found in the very southernmost part of San Diego County, and in general a flower is needed to distinguish it from C. ganderi.
For the geographic distributions of those four chollas, see the maps on this 2008 page: Opuntia echinocarpa, O. ganderi, O. parryi, and O. wolfii: Locations.
Distinguishing Cylindropuntia bernardina and C. ganderi is quite easy at the population level, since C. bernardina generally has some stem segments longer than 26 cm, whereas C. ganderi only extremely rarely has stem segments longer than 26 cm. The fundamental reason for this is that C. bernardina has the ability to grow its stem segments over two years, whereas C. ganderi cannot do that. C. bernardina also has longer tubercles on average.
Although there is considerable overlap in the histograms of stem segment lengths for each species, if you look for the longest stem segment in at least five plants in a given area and find it is longer than 26 cm, and especially if you find multiple plants or multiple stems with similar long stem segments, you have a population of C. bernardina. If you don't find any plants with stem segments longer than 26 cm, you have a population of C. ganderi.
With practice, you quickly no longer need a ruler to determine a population, since the longer stem segments of C. bernardina in about half of the plants in a population become obvious to your eye.
But there are always some plants that try to fool us, or populations that are not clearly one species or the other. In those cases, measurements are needed to distinguish them. This page presents those measurements.
Fig. 2 shows a plot of the typical longest tubercle length, and maximum stem segment length, measured on individual plants of C. bernardina, and the similar plot for plants of C. ganderi. The plots have the same range in values for the coordinate axes.
Each plot contains plants that were in almost all cases measured in areas where only one of the species grew, to avoid any potential problems of intergradation that might occur in areas where both species grow.
The C. bernardina measurements came from plants in the San Gabriel Mountains, San Jacinto Mountains, the San Felipe Valley area of San Diego County, and along SR94 in southernmost San Diego County. They include plants with the full variation in spininess of the fruit, from almost no spines to dense spines.
The C. ganderi measurements come from the area just west of Borrego Springs, Culp Valley, the Santa Rosa Mountains, and the southernmost Shelter Valley area along S2.
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| Fig. 2. Plot of tubercle length vs. maximum stem segment length from individual plants of Cylindropuntia bernardina (top), and C. ganderi bottom. The plots use the same range in values for the coordinate axes to facilitate comparison. |
Plants of each species plot almost uniformly throughout the rectangle defined by the min and max values of each characteristic, with only a single outlier for each species, except that there are fewer plants of C. bernardina with tubercle lengths longer than 25 mm. The tubercle length ranges from 16 to 35 mm for C. bernardina, and 11 to 25 mm for C. ganderi. The maximum stem segment length ranges from 14 to 43 mm for C. bernardina, and 10 to 26 mm for C. ganderi.
There is considerable overlap in those ranges, as shown in Fig. 3.
Fig. 3. Merged plot of tubercle length vs. maximum stem segment length from individual plants of Cylindropuntia bernardina and C. ganderi.
There are 55 specimens that fall in the overlap region in Fig. 2, and 68 specimens that fall in the unique regions for each species. Measuring a single specimen will thus fall into the overlap region 45% of the time, and in the unique regions 55% of the time.
The best way to get a solid determination is to measure five nearby plants. If those five plants are a population of C. bernardina, and the measurements of those five plants are uncorrelated, 97% of the time one measurement will fall outside the overlap region, uniquely determining the species for those five plants.
Such measurements are illustrated in Figs. 4 and 5.
Fig. 4. Measurements of four plants of C. bernardina from SR371 northeast of Anza in Riverside County. Three out of the four measurements fall into the area of the plot where only C. bernardina is found, implying that all four plants are members of the C. bernardina population.
Fig. 5. Measurements of five plants of C. ganderi from Mason Valley in San Diego County. None of the five measurements fall into the area of the plot where only C. bernardina is found, implying that all five plants are members of the C. ganderi population; see the first iNat post of those plants and the second post. Five additional plants in a nearby location were also measured, and none of those five fall into the area of the plot where only C. bernardina is found, either; see their iNat post.
For more information about these two species, including how they were erroneously discriminated in the past, see my 2007 webpage on "Intergradation" between Opuntia parryi and O. ganderi, and references therein.