Barrel cacti of the US and Mexico

Some of the most vicious cacti of the American southwest and Mexico are not trees (like the saguaro), prickly pears (Opuntia), or chollas (Cylindropuntia), but globular to columnar plants known as barrel cacti.



The barrel cacti include plants up to 10 feet tall and several feet wide, as well as many smaller variants much more suitable to long-term container life, though all of them can be kept that way for at least a few years as juveniles before their size gets to be an issue.



The barrel cacti have defined ribs and are all spiny, sometimes forming mounds. They tend to make scaly (sometimes hairy) buds and fruit. In some cases, the fruit is edible.



These plants are specialists in survival. They prefer rocky substrates (some grow on limestone in nature) and often tolerate extreme conditions including heat, sun, fire, drought, nutrient poor soils, and hungry animals. As garden plants in arid climates, their durability is a real asset. A habitat plant recovering from brush fire here:



Barrel cacti enjoy good drainage and lots of light. They do not tolerate much cold or excess rainfall, especially not the combination of the two. But they do tolerate neglect, once established in a landscape location.



Their growth rate is slow, but most plants flower yearly at or near the apex once they have reached maturity, usually somewhere between 6 and 12 inch pot size. Water regularly during the growth season, ideally waiting for the soil to go dry or nearly dry at depth each time before watering again. Reduce winter watering significantly in climates with winter chill.



This group remains poorly defined, and the name barrel cactus means different things to different people. In this brief photographic review I will talk about some of the more common and colorful plants in cultivation from the United States and Mexico. These plants are usually called biznagas (or bisnagas, same pronunciation) in Spanish-speaking territory.



I will also attempt to explain the current scientific names and how they have recently changed. The names below represent the status quo as of mid-2024, according to the Catalogue of Life, and are very much subject to further change and revision.



The golden barrel, or asiento de suegra in Spanish, is nearly extinct in habitat (north-central Mexico) but very common in cactus collections worldwide. It grows up to about 2 feet wide and tall (more in extreme old age) with distinctive stout, vicious yellow spines and bright yellow flowers.



There are also white-spined and short-spined versions of the golden barrel, neither of which is a great improvement on the ordinary form in my opinion. The white-spined form (but not the normal form) fluoresces brightly under UV illumination.



This species has recently been moved from Echinocactus to its own monotypic genus, Kroenleinia, based on genetic information indicating it is quite distinct from the other group. It normally branches sparsely, if at all, but it is fairly often cored in nurseries to produce bubbly, multiheaded versions at a higher price.



Two members of Echinocactus also deserve attention:

Echinocactus texensis, from the southwestern US into northeastern Mexico, reaches a much smaller size and may be a better long term choice in a container. The flowers are pinkish or white with a reddish center, and the fruit is fleshy. This plant is touchier as a juvenile than most barrel cacti in my experience.



Echinocactus platyacanthus, from north-central to south-central Mexico, may be the largest of the barrel cacti at maturity, reaching several feet tall and 3 feet wide, though a small plant won't reach this size in your lifetime. The biggest plant I have seen was 12 feet tall.



This cactus has a difficult relationship with Mexican popular culture, where it (and a few related plants) are harvested in order to prepare a much enjoyed holiday candy called acitrón from the pulp. Harvesting wild plants for this purpose is now illegal, and environmentally friendly alternatives are available, but enforcement may not always catch up with people's bad habits.



Ferocactus is the genus most people think of first when they hear the name barrel cactus. It used to include a number of plants which were recently moved to other genera (Bisnaga, Parrycactus); those plants will appear separately in this list. Ferocactus is also close to the North American Leuchtenbergia and Thelocactus, among other cacti. Thelocactus setispinus in particular is quite easy to confuse with a juvenile Ferocactus, though it grows smaller, flowers sooner, and has less vicious spines.



Ferocacti occupy some of the harshest deserts of North America (eg. F. wislizenii and F. cylindraceus, from the Sonoran Desert), but a few also have found niches in more moderate climates. For example, the coastal F. viridescens may only experience temperatures above 90°F a few days a year in habitat; other members of the genus are found at higher elevations without the extreme punishing heat of the low desert.



This group usually produces fruit that is hollow inside, releasing the seeds through a basal pore when it is detached. Most of the members of the newer and reduced Ferocactus are from Baja California, northern Mexico and the southwestern US. They mostly appear to be self fertile (if not particularly so) in my experience.



Ferocactus latispinus, which is widespread in Mexico, is also quite common and relatively easy in cultivation. It has some of the most attractive spines in this group, especially the flattened, ribbed, hooked, usually intense red central spine. The red color of this and other barrel cacti is most intense when the spines are wet. The flowers (usually pinkish purple) are also quite pretty, appearing around the 6-8 inch pot size.



F. wislizenii, from the Sonoran Desert of Arizona and northwestern Mexico, can be an imposing, well-armed plant, potentially growing taller than a human in extreme old age. It is a great choice for low desert locations, along with the golden barrel. The flowers are yellow, orange, or red.



F. cylindraceus, which has gone through its own set of name changes, is found in the southwestern US, as well as northern Baja California and Sonora in Mexico. It tolerates serious heat and is frequently associated with agaves and ocotillos in nature. It has yellow flowers and may also grow tall in old age. The spines are curved to hooked, of varying colors including intense reds and yellows in certain populations, and its radial spines tend to be much thinner.



F. gracilis is among the best red-spined cacti, with intense red or orangish red flowers. It occupies the harsh central desert of Baja California and is often found with the giant cardón and cirio in habitat.



F. pilosus, from north-central Mexico, also has impressively red spines (sometimes other colors) and intense red (sometimes yellow) flowers. It has fewer, sharper ribs than gracilis and potentially grows much larger. This species gets its name from the radial spines, which are quite variable but often like bristles or hairs. Some populations are prone to basal branching and form a nice clump over time. This is a faster growing plant than many other Ferocactus species, but it does still take its time to grow up.



F. chrysacanthus, another Baja California native, is a smaller, intensely spiny plant with yellow spines (among other colors). It is solitary and may grow up to 12 inches wide, though often ends up smaller than that. An excellent, ornamental, slow-growing, long-lived container plant for arid climates. This one in a 6 inch pot is about 5 years old:



The green F. robustus is an extreme outlier in terms of form, forming huge spreading clumps of dozens of stems in old age. This native of the south-central Mexican state of Puebla is also a relative geographic outlier for this genus, which is mostly found further north. Its branchy habit makes it a good source for cuttings to root and start new plants, though it grows well from seed, too. Provide ample space for this plant in the garden, as its potential landscape size may be deceptively large.



Four species of Ferocactus were recently moved to the new (resurrected) genus Bisnaga. They are genetically distinct from the remaining members of Ferocactus; all make yellow flowers and a juicy, fleshy (and often delicious) fruit.



Bisnaga histrix is among the largest barrel cacti, easily confused with a squat Echinocactus platyacanthus at maturity, favored by botanical gardens for impressive group plantings. The fruit is extra sweet and juicy, enjoyed in some parts of Mexico as guamishi (among other spellings). Some plants may flower and fruit at the 8 inch pot stage; other clones may not do either until after they fill a 12 inch pot.



B. glaucescens is a similar-looking plant, also with pale yellow spines, but bluer, smaller in final overall proportions, and usually more likely to branch at the base or above. Its fruit is white and relatively small. This is probably the most common member of the genus Bisnaga in cultivation.



The resurrected genus Parrycactus currently houses 5 former members of Ferocactus, all found in Mexico. These plants are closely related to each other genetically, and distinct from Ferocactus.



Of these species, perhaps the most notable is Parrycactus flavovirens (Puebla, Oaxaca), which is an exception like F. robustus in forming large multiheaded clumps over time. Its flowers are yellow or reddish.



Finally, a brief note that the barrel cactus form is not limited to these genera or this part of the world. There are lots of similarly shaped and similarly spiny cacti from South America, including the colorful Denmoza rhodacantha from Argentina, which has very attractive reddish spines but produces tubular flowers very unlike the cup-shaped or spreading ones of Ferocactus and its close relatives.