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One of the Oddest Flowers: Desert Trumpet

Desert trumpet | Photo: Ken-ichi Ueda/Flickr/Creative Commons License

From the Joshua trees and saguaros to the raggedy chollas, there are a lot of odd-looking plants in the desert. You'll have to get out of your car and look around to really get to know one of the oddest. It's the "desert trumpet," and it's a major if often overlooked feature of the California desert.

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As soon as you notice desert trumpet, you start seeing it everywhere. Desert trumpet, a.k.a. Eriogonum inflatum, isn't a picky plant. Calflora lists its preferred elevational range as "between -50 and 6,561 feet." It's equally at home on the shores of dry lakes and the edges of mountainous pinyon-juniper forests. In fact, it's a common resident of just about every vegetative community in the California deserts, from those upper-altitude forests to the creosote flats, along with the Joshua tree forests between the two. It would seem the winters are a bit too hard for desert trumpet once you get north of Bishop, but the plant thrives throughout the whole range of deserts to the south -- and even leaks out into the southern, kinda-deserty end of the Coast Ranges as well.

Many of the 200-odd other species and subspecies of Eriogonum native to California live squarely on the boundary between perennial herb and fragile shrub, their above-ground portions either staying alive or dying back depending on exposure, eweather, rainfall, and -- seemingly -- their shifting moods. Eriogonum inflatum tends more toward the perennial herb side of things. Its basal rosette of small, rounded leaves mostly dies back in the winter, though I've seen them stay kind of green in sheltered spots during broiling summers and snowy winters.

That rosette of leaves puts out a flower stalk in spring that bears panicles of tiny flowers, mainly yellow ones, though I've heard reports of a few pink-flowering varieties here and there. They're blooming in my neighborhood as we speak. The flowers are pretty, but they're inconspicuous:

Desert trumpet flowers | Photo: Chris Clarke

It's fair to say that even those desert plant enthusiasts who notice and admire desert trumpet might have to think for a moment before they tell you what the leaves and flowers look like. The most noticeable part of the plant is neither leaf nor flower, but the stem that connects the two. The plant's elongated, swollen flower stem, which gets between one and (occasionally) three feet tall, gives the plant both its common and scientific names.

Desert trumpets with green stems | Photo: Fool On The Hill/Flickr/Creative Commons License

The main flower stem swells in its upper part to as much as an inch wide, tapering back to a node where it then branches into two or three smaller stems that bear the flowers. Those subsidiary stems sometimes swell a bit as well. Over the course of a typical growing season, the desert trumpet gets most of its photosynthetic oomph from that swollen green stem: it's got more surface area than the leaves, and its shape and vertical pose make it an efficient solar collector. Some part of the stem is always pointed at the moving sun.

For a long time, it was thought that the swelling was caused by gall-forming insects, with the main suspects being tiny moth larvae of a species of wasp. You still see confident assertions in print that Onyerus wasps drill holes into the stems, pack them with captured insect larvae, then lay their eggs on the larvae, essentially turning the stems into a house of horrors. That story comes from naturalist Edmund Jaeger's field guide "Desert Wild Flowers," and is incorrect in a couple respects. First off, "Onyerus" originated as a typo. There's no such wasp genus. The closest such wasp name is Odynerus, and Jaeger may indeed have seen one crawling in and out of a desert trumpet stem, but they usually nest in the ground.

The plant does attract insects. Some lay eggs in the trumpets, others on the leaves or the outside of the stems. Eriogonum in general is a preferred "butterfly plant," and desert trumpet is no exception. It's not unusual to find a caterpillar beneath the leaf rosette, happily munching away.

But there's no real evidence that insects cause the stems to swell. As it turns out, the stems swell even in the absence of insect infiltration. It's usually pointless to ask why a particular feature of an organism evolved, but the desert trumpet's hollow stem serves as a reservoir for carbon dioxide. (The air inside the stems, in fact, contains enough CO2 to kill insect larvae. Careful insect mothers who do lay eggs in trumpet stems drill a hole in the stem to ventilate their offspring.) Plants breathe CO2 when they're engaging in photosynthesis, and higher concentrations mean more efficient turning of sunlight and water into plant tissue.

What's more, the stems don't lose water to the outside air as readily as the plant's leaves do. Which makes those swollen stems very efficient little photosynthesis engines indeed. That's definitely enough of a boon that the first Eriogonum inflatum to develop swollen stems may well have thrived relative to its uninflated cousins.

It wasn't a slam-dunk advantage: there is a form of the species with uninflated stems, which has long delighted aficionados of fanciful botanical names with the monicker Eriogonum inflatum var. deflatum.

The stems provide enough of a photosynthetic advantage with a low enough necessary investment in water that they often stay green long after the plant's leaves wither and die back. One study suggests that those stems may do between two thirds to three quarters of the plant's photosynthesizing, while accounting for only around half the plant's water consumption.

But like all things living, those stems do eventually die. The plant absorbs what water it can from the living tissue in the stems. The green fades. At first the stems turn a deep red-brown, like the bark of a manzanita. They gradually fade to a pale straw color.

And that's how they stay, standing stock-straight for years after they die back, a desert-wide bouquet of dried flower stems that offer shelter smaller plants and animals for years after blooming. And if you don't get out of your car and walk around, you may miss them altogether.

Desert trumpet | Photo: Florian/Flickr/Creative Commons License

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About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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