Two fruits from banana yucca (Yucca baccata) in late June 2019.

I have been gardening in Arizona for 20 years, and I have hundreds of banana yucca plants (Yucca baccata) that are native to my property. I’ve seen thousands of individuals of this widespread species over the two decades I’ve lived and traveled in the West across half a dozen states where they grow. But it is only now, in July 2019, that I have seen seed pods on any of these plants. Just two of them, on the same individual, growing right in front of my house. I waited until they were mostly dry before harvesting and photographing them, and clipped them off of the plant before they could be stolen by a rodent or some other critter. One can see why these were called “banana yucca”, for the elongated pods that do somewhat resemble bananas, at least in shape if not much else.

Detail of the two Yucca baccata fruits, showing the dried floral remains clinging to the base of the pods, which I had removed in the first photo.

I’ve spoken with other well-informed growers about this matter in years past, and we all agree that for whatever reason, Yucca baccata is very reluctant to set seeds. As a member of the sizable Yucca genus they have specialized pollination relationships with one particular small moth species, mainly in the genus Tegeticula, which is the only effective pollinating agent for yuccas. Each yucca appears to have its own specialized moth that serves only that type, with little to no crossover occurring over to also serving nearby yuccas. Not even when they grow intermingled in the exact same landscape.

The plant from which the twin fruits came, as seen before harvesting the pods. It’s a bit of hide-and seek to distinguish the pods from the dry floral parts.

A cropped-in version of the photo above, showing the two well-camouflaged fruits, which are shaped at least as much like chili peppers as they are shaped like bananas.

Why is seed set so rare for this species? Is the banana yucca moth that pollinates it rare for some reason? Has this small, drab insect been made nearly extinct over large parts of its range? Has climate change played a role in making much of the habitat too hot and dry for the moths, even as the plants themselves persist? Is this a normal situation, or were banana yuccas previously fairly reliable with their seed pod production? The other yucca I have here at D:F Ranch is the Joshua tree (Yucca brevifolia) and the trees are quite good at setting numerous pods after wet winters, such as 2018-2019 was. I’ve seen the Joshua trees produce thousands of seed-laden fruits multiple times in 20 years, while the banana yuccas set nearly none in spite of regular blooming at roughly the same time as their neighboring Joshuas.

The plant in context with portions of my house and garden.

There is also a third yucca type growing locally within my area of Mohave County, Arizona, that being Mojave yucca (Yucca schidigera) which is not found on my property but is present within about 30 miles of here. Yucca schidigera commonly grows with both banana yuccas and Joshua trees over much of its higher-elevation natural range. The Mojave yucca seems to be intermediate in terms of seed set, being more regular than banana yuccas, but much less regular than Joshua trees. I’ve seen seed crops on Mojave yuccas at least two times since 1999, but that means they are only fruiting abundantly once every decade or so, as opposed to every other year for Joshua trees. (2019 is such a year, by the way, and the Mojave yuccas near Kingman AZ are loaded with seed pods.) Again, what is the cause of this dynamic, and why is the Mojave yucca moth rarer than Joshua tree moths but more common than banana yucca moths? Mysterious questions….

Scene in my garden. The narrow-leaved plant in the background left is Yucca thompsoniana, which I had just planted literally only 5 days before. It was a 6 foot tall salvage plant from a friend’s former nursery and large yard/cactus garden in Morristown, AZ . My friend had to move, sold the place, and the new owner of the property decided to reduce the number of cacti and succulents in the yard. I was fortunate enough to be able to salvage the Thompson yucca plus a number of other species I was pleased to rescue. Yuccas of different species, especially large ones, are always welcome at my place!

Fortunately for the banana yuccas, they do not appear to be suffering badly despite the lack of seed reproduction. The plants are widespread and common over large areas, and they are capable of vegetative propagation via their thick underground rhizomes, a trait that also makes them somewhat fire-resistant since they can regenerate after burning. They are certainly not primarily reliant upon seeds to persist in the ecosystem, although one would think that over the long run it might potentially impact them to not be doing more of it in terms of genetic diversity. My fellow nursery growers do tend to agree, however, that whenever you see seeds on Yucca baccata that you should gather them and sow them, since it might well be a decade or more between opportunities to do so.

A few examples of the generous bloom of banana yuccas this past spring. These photos were taken on Friday, April 12, 2019 when they were in prime shape. The flowers were just starting to open and many buds remained amidst a carpet of Mexican goldpoppies (Eschscholzia mexicana) about a half mile south of my cactus rancho. None of the numerous flower spikes set any pods to my knowledge. They almost never do….

If anyone has observations, knowledge of, or theories about lack of seed production in Yucca baccata, please share it in the comments. Thanks!

Detail of the lovely, waxy blooms of Yucca baccata. The buds are frequently a reddish-purple tint. The blossoms are home to numerous flower thrips, tiny sap-sucking insects that swarm many plant species, as well as feeding upon foliage and other vegetative parts.