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Taxonomy of Club Chollas

Dave Ferguson, 2007

The generic placement of "Grusonia" parishii and the other club chollas is a bit of a problem in limbo right now. For the moment the placement of Club Chollas into Grusonia seems to have caught on, and seems to be the most popular treatment. However, it may not last long.

Grusonia bradtiana was for a long time considered to be the only species in its genus. It is very like Cylindropuntia (North American chollas) in structure, seeds, fruits and flowers, but the stems are very thick, segmented, and tends to lay over sideways as they grow. The main dominant stems of Cylindropuntia are nearly always continuous, with only sometimes a constriction at the meeting of each year's growth (though lateral branches are often jointed). The stems of Grusonia bradtiana tend to make few lateral branches (most, but not all Cylindropuntia produce lateral branches in whorls near each joint). The tubercles are fused into ribs, but they are on some Cylindropuntia species as well. The spines of Cylindropuntia have a papery sheath that covers the whole spine. In Grusonia bradtiana the spines have only a trace of a sheath at the very tip, and that usually falls off soon after the spine matures. Another minor difference is that in Grusonia the stems tend to be jointed, even the main stems, while in Cylindropuntia the main stems are mostly continuous without joints. The fruit in both Grusonia bradtiana and most (if not all) Cylindropuntia are very thick-walled and generally rather chunky (not much longer than wide).

The club chollas have stems that vary in shape, but they are segmented as well. The segments in most are thick and roughly club-shaped, and the plants are mostly low spreading things. The tubercles of stems mostly don't form ribs. The spines have only a bit of a sheath at the tips. The fruit in most are elongate, conical, and rather thin-walled when mature. There several species in this group, and the limits of the species are not well studied yet. One species (marenae) with particularly long and slender stem segments and fruits was put in the Genus Marenopuntia, but the shape is the only distinction. Another species (pulchella) with small rather soft joints and a large tuberous taproot has been split into a lot of names and is sometimes called Micropuntia. As a group, these have all been called Corynopuntia, and more recently were all lumped into Grusonia.

All of these species have been placed in the genus Opuntia as well.

In 2003 Patrick Griffith published results of a molecular study in Haseltonia (v9: 86-93). His results point to Grusonia in the large sense not being a natural group, and that they should probably be split into Grusonia for bradtiana, Micropuntia for pulchella, and Corynopuntia for the rest. Or, they could all be considered groups within the cholla genus Cylindropuntia. A comparison to how they are related might be to use a family tree. The species lumped into Grusonia aren't all "brothers and sisters" on the tree, just most of the club chollas. The species pulchella and bradtiana are more like second or third cousins, but Cylindropuntia species are first cousins to club chollas. So, according to these results, Cylindropuntia and Corynopuntia are closer to each other than to M. pulchella or G. bradtiana, and G. bradtiana is next closest, with M. pulchella most distant of the group. They are all closely related though, and could be easily all called Cylindropuntia, with the other groupings as subgenera. Also very close to all of the above is Pereskiopsis.

So, I suspect the jury is still out on the genus name for these. Right now, I'm tending toward calling most of the club chollas "Corynopuntia", and that would make it Corynopuntia parishii, rather than Grusonia parishii. Doesn't really matter which genus you use for now, as most people will be able to figure it out.