Foreword: I made this particular blog post knowing that Opuntia woodsii was not likely to be a valid name, but did so without an adequate understanding of the genetics of pink to red-flowering hexaploid Opuntias in southern Utah and northern Arizona. In fact, I am still not very clear on hexaploid Opuntias of said region, although there has been some discussion on Facebook as a result of my post that I shared there by several people who are better-versed in the complex than I was/am.

Therefore I will add this caveat to the blog post at the beginning, added a few days later on Sun Dec 9, 2018. Opuntia woodsii was not a valid published name and no official herbarium specimens of it under that name were ever deposited in any university or research institution, and therefore it really should not be used. But I don’t particularly care to rewrite the entire blog post (although I perhaps should) and the name does have some established loose meaning to prickly pear enthusiasts, even if they dislike the name for being inaccurate. It is for this admittedly slightly lazy reason that I will retain it with this explanation and disclaimer up front before people read the text below.

Here’s the scoop as I understand it: It’s complicated and details are still being worked out as of late 2018 and might never be fully settled. But the complex of larger and densely flowering Opuntias in the Virgin River and Santa Clara River watersheds of Washington County, Utah are hexaploids (having six full copies of chromosomes, rather than the more typical two in most organisms) that combine traits of both Opuntia engelmannii and Opuntia phaeacantha most strongly. Hexaploidy is prone to some pretty diverse physical expression since there’s a lot of ways for six sets of gene copies to be expressed. This includes flower color, plant size and growth habit, pad shape, spination, and fruit traits as the most salient ones. So these hexaploid “Opuntia woodsii” simply come in an array of diverse floral colors and plant morphologies.

I was incorrectly thinking of the pink or red flowering forms as being O. woodsii, and the yellow forms as O. engelmannii with varying degrees of O. phaeacantha mixed in. In truth they are all hexaploid hybrids containing a probable majority of O. engelmannii genes with strong O. phaeacantha components. Flower color is but one variable and is not necessarily indicative of an accurate identification process, if such a thing even exists in the group. Ploidy levels are impossible to determine visually alone and require a certain amount of analytical skill and scientific equipment that I don’t have. Genetic research has been revising old ways of understanding how plants are related to one-another, and upheaval has been a recent norm.

Complicating the picture is the fact that across other parts of the Colorado Plateau surrounding the Grand Canyon to the east, other Opuntia species start to manifest their influence. These other northern and eastern species adding genes into the hybrid swarm include O. nicholii, O. hystricina, O. pinkavae, O. erinacea, and O. aurea. There are possibly other interfaces with western species such as O. charlestonensis and O. vaseyi. Some of these species are tetraploids which can breed with hexaploids but this results in mostly sterile pentaploids. It’s rather a taxonomic mess with few clear lines. Although the results in the form of the plants are quite awesome and intriguing to seek out and find. Ultimately, the plants don’t care what we call them, as long as they are fit enough to survive and reproduce into the future.

TL;DR – Opuntia woodsii isn’t a valid name, and most plants are hexaploid hybrids comprised mainly of O. engelmannii and O. phaeacantha with smatterings of other species thrown in in various ways and across different geographic regions. But I will use O. woodsii as a shorthand in this post regardless knowing that it’s not correct, because it can be understood to mean a pink or red flowered hybrid, even though this is quite incomplete.

Now, let’s get to the photos, shall we?

This Opuntia woodsii growing in southwestern Utah shows precisely why I love the botany of that region. The red rocks and complementary-flowered plants are beyond compare.

In May 2015 I took a trip with another cactus fanatic friend to seek out various species of prickly pear cactus (Opuntia spp), primarily in northern Arizona and southern Utah. That time of year was chosen because it would offer the best possibility of seeing various types across their range in some stage of flowering, which would enable selection based upon features like bud count, floral coloration, and even new spring growth which are difficult or impossible to determine at other times of year.

I am totally in love with this color and the huge number of flowers found on some clones of Opuntia woodsii. I can’t wait until mine reach this size in my gardens!

I collected a number of pads of the prickly pears featured in this post growing near St George, Utah. From a horticultural perspective these were utterly outstanding for their size, flower brilliance, and their high bud count. Floriferous plants are desirable not only when in bloom, but also after the fruits ripen to their purplish-red color, which is useful for both wildlife and human consumption. Also, since the colorful fruits can be as decorative as the showy flowers, and last for a longer period of time, selecting for plants that have lots of buds is horticulturally useful from several standpoints.

This region of Utah contains what might be considered a “hybrid swarm” comprised of numerous plants of several species in a population with active gene flow between them. This leads to many interesting variants spanning the entire spectrum of possibilities of the relevant types.

This post mainly features plants of both Opuntia engelmannii (yellow flowers) and O. woodsii (coral pink flowers), with a couple more species thrown in for the sake of diversity and completeness. The official naming of O. woodsii is a bit controversial, in that it is fairly distinctive and has a defined geographical presence in the canyons and mountains of northern AZ and southern UT, but is not necessarily a fully recognized species either. It is possibly a complex, stable hybrid of O. engelmannii and O. phaeacantha, perhaps with genes from other species mixed in as well. For the purposes of brevity I will simply refer to them as O. woodsii, however, while recognizing that this is probably not actually a taxonomically valid name. (It is, however, much shorter to write out. ) Whatever the provenance of the species, these Utah coral- to salmon-flowering forms are certainly strikingly attractive and most worthy of wider cultivation.

Halictid bees gathering pollen for their brood from prickly pear flowers.

A close-up of a flower of Opuntia woodsii reveals how attractive they are to small green sweat bees, likely in the bee family Halictidae. There are hundreds of Halictid bee species in several dozen genera in the desert southwest, and many are important pollinators of numerous native plant species. The iridescent metallic green color is pleasing to the eye, isn’t it?

I love the color of these small, inoffensive bees. The name “sweat bee” comes from the attraction certain species have to perspiration, although many of them show no interest in humans whatsoever.

A different type of bee also enjoys the pollen of this Opuntia woodsii flower. Prickly pears produce abundant quantities of pollen in each flower, which is a primary food source for these bees as well as for beetles, flies, and other insects.

This photo taken on May 20, 2015 illustrates why coming in mid-spring was a good choice. All of the plants are in bloom, enabling discerning selection for any worthy traits useful in desert landscaping and horticulture.

Red canyons cut beneath black mesas in far southwestern Utah.

This part of southern Utah has a very unusual blend of volcanic rocks and sedimentary rocks. These two types of strata do not often exist in close proximity due to their very different modes of genesis, but here they do, leading to some very pleasing combinations of red and black stones in direct contact with one-another.

Add the flora to the geology of this place, and you have some really lovely and artistic scenes possible.

Colorful lichens plaster the north sides of both the sandstones and the basaltic lavas.

Lava benches separate the thick beds of red sandstone in this part of southwestern Utah.

These black basaltic lava flows are much younger than the red sandstones they erupted through. This odd geological pairing comes from the way plate tectonics and mountain orogeny tore apart the earth’s crust in this region, with the thick shield of sandstones, limestones, shales, and other sedimentary rocks being uplifted to the east to form the Colorado Plateau. Meanwhile, in the Great Basin and Range province to the west, the earth’s crust experienced thinning and rupturing as fault-block mountains rose and valleys sank. This allowed for volcanic activity to break through in places, including here at the juncture of these two large and primary physiogeographic provinces of western North America.

Where’s Waldo? Can you spot the leprechaun?

I love the sweep of the mountains in this region, where the Mojave Desert meets the Colorado Plateau. This intersection of two different geological and ecological provinces contributes much to the beauty and biodiversity of the area.

The two flower colors of Opuntia woodsii and what is probably Opuntia phaeacantha mix together on plants intertwining their pads. It’s a good look.

Large individuals of Opuntia engelmannii thrive below the dark outcrops of lava basalt in this Utah canyon, measuring two meters across and almost a meter tall. They are nearing the northwesternmost edge of the range for this species.

Hitting these populations of prickly pears in bloom was the idea, and fortunately we succeeded. Ten days before and they would mostly have been buds, and ten days later the majority of flowers would already have been open and closed.

These Engelmann prickly pear have gorgeous bright yellow flowers on sturdy plants 2 to 3 feet tall and 4 to 5 feet wide. These tolerate temperatures to near 0 F (-15 C) without damage in their native Utah habitat.

What appears to be a prickly pear with two different flower colors is actually the progression of the flowers as they age on an example of Opuntia engelmannii. They start out as a strong yellow, and fade to a pale orange on their second day. They close at the end of day two and if pollinated go on to set the fruits.

O. engelmannii and O. woodsii grow side-by side, indicating probable genetic mixing between them as they cross-pollinate and create offspring that contain traits of both sets of parents. Indeed, when out of bloom the two species are hard to tell apart based upon foliage alone.

This plant doesn’t have the highest bud count, but the purple shading of the new pads as they develop is quite unique. My guess is that it’s a hybrid of mixed parentage favoring O. woodsii, but this is speculation without doing a DNA analysis. It would be worth trying to breed a plant with both purplish pads and tons of flowers. That would be a winner!

Another floral trait one might appreciate is large size, such as this O. woodsii with the largest flowers we observed on the entire trip. Nearly 80% larger than a more typical specimen, this size plus the sunset-like color shades makes this a singularly attractive clone worth propagating and introducing into cultivation.

As mentioned earlier, high bud count is also a horticulturally desirable trait, as exhibited by this Opuntia engelmannii. Once collected, the numbering written on each pad in permanent marker (along with ID tags) helps to determine what it is when it is in its vegetative state. Identity is easy to lose track of when the plants are not in bloom…. which of course is most of the year.

Another high bud count plant, this time on O. woodsii. Duly noted as such in the marker notes. Many pads had 6 to 12 buds on each pad, which provides for a generous color show both in bloom and in subsequent fruit.

One, two, or three cacti?

I took this photo for two reasons. The first is because it shows how closely integrated the growth behaviors of various plants are around this region, with different flower colors mixing intimately. While this looks like a single plant, based upon flower colors it is actually at least two, and possibly three, all growing in a soil pocket upon andesite, another volcanic rock type of this region.

The other reason is because it shows that sometimes when taking cuttings of prickly pears, it’s best to remove the buds once properly recorded and labeled so that the plants don’t waste resources in trying to finish blooming once separated from the mother plant. Prickly pears will often continue to draw upon stored water and nutrients in the disjointed pad in order to complete flowering, often at the expense of the pad’s survival. It is seemingly a bit antithetical to cut all the flowers off, because the plants were selected precisely for these traits; but it is to preserve their strength so that they can root, grow, and produce more flowers next year.

This is Opuntia erinacea, which is another species that lives in this southwestern corner of Utah.

Another associated cactus species found in the area is the silver cholla, Cylindropuntia echinocarpa. Great combo to see this plant with the red sandstone, as it usually occurs in habitat with little or none of that stone type.

I came across this pack rat (Neotoma sp) trying to hide in a clump of Opuntias. These rodents build their nests among and often feed upon the prickly pears – in fact, cacti provide as much as half of a pack rat’s diet when the plants are available.

Wait! What is this oddity I see?

It’s some sort of monstrose growth in an Opuntia woodsii. Definitely atypical.

Close up of the unnatural growth on this prickly pear. Note the dead tissues below the currently alive, pinkish-red growth.

I haven’t researched deeply into what precisely might cause this sort of abnormal growth, but I have not seen it before in cacti. Note that this is not cresting or monstrose growth in the same way that is reasonably well-known in cacti and other succulents. It appears to be a neotenous growth form, where juvenile characteristics are retained, rather than maturing into adulthood.

We wanted to see if we could propagate it.

We did make a cutting of this unusual growth, leaving part of it on the plant just in case it was somehow important for a future we cannot currently imagine. But the cutting refused to root and died rapidly within a few weeks, indicating that the cellular abnormality was not viable off of the mother plant. Dead growth is actually visible on the cactus in the photos above as well, indicating that it is not useful or sustainable to the plant itself either. I speculate that one cause might be pathogenic, such as a virus, or perhaps some sort of parasitic Eriophyid mite, similar to those which cause tumors and distorted growth in plants such as aloes, agaves, and certain oak galls. In any case, I’ve not seen it before or since, just this single plant.

Another interesting plant. Potential hybrid?

One other putative hybrid we discovered was what I presume is a cross between Opuntia erinacea and O. woodsii. This is purely speculative based upon the flower color and the pad size and spininess and the upright growth habit, and it’s possible that I am mistaken in assuming that those are the two parents. For all I know it could be a three way hybrid involving back-crossing, or another species also found in the area, such as O. aurea or even yellow-flowered O. engelmannii. (Yellow flowers appear to be recessive traits in many hybrids involving one pink and one yellow parent – the pink tends to dominate in the first generation offspring, assuming that this is an example of such a plant.)

Different angle of view on the mystery hybrid.

Whatever the parentage of this presumed hybrid, what is clear is that it’s decidedly worth growing in a garden. The pads are large, about 6 inches in top diameter by 7 to 8 inches long, and the plant possesses an upright growth habit reaching a bit over two feet tall thus far. The dense spines are more indicative of O. erinacea, as are the brilliant magenta flowers, and the dry, seedy mature fruits we found laying on the ground. But the large pad size calls forth the larger O. woodsii, which itself is probably a hybrid, thereby making this a likely 3-way back-cross with genes from several species.

Given the habitat, this plant can clearly tolerate significant cold into the high single digits upon occasion. If this is the result of some random bee-facilitated mating event going back a few decades, then it’s a rather unique and special gem. We did take a few cuttings, taking care to leave the main mother plant behind to keep growing in situ.

Let’s just repeat this photo, because this is SUCH a terrific plant to keep in a desert garden.

It has been several years since the so-called Opuntia Quest trip, and many of the cuttings are doing well in their pots and have been planted in the ground, where they are still young but starting to gain some size. My Arizona garden is at least a full zone warmer than this Utah location, and I have had some issues with rabbits trying to consume young plants before they can develop into clumps large enough to resist some browsing. But in most USDA Zone 7 to 9 deserts any of these species and hybrids featured here ought to be good choices to grow.

Detail of several flowers from the plant above. Such a showy display!

Oh yeah, all of these glorious colors are going to look SO GOOD in my gardens in a few more years. I can picture them now, mixed in with the golden barrels, agaves, and columnar cacti. Happy thoughts!