Cercocarpus Part 2: The Other Mountain Mahogany

Last Fall I went through a period of searching for, and finding, a number of rare hybrid oaks. These oaks will be something I cover in a future post, but the important thing about these hybrid oaks as relates to this post is that the leaves of these oaks are persistent much later in the season than “regular” Gambel Oak, meaning that oftentimes the hybrid oaks will bear green leaves when the surrounding Gambel thickets are brown and bare.

Because of this, late October and November are the best times to search for these oaks, and doing so typically involves scanning a section of foothills- from foot, bike or car- and seeking out clumps of green on an otherwise brown slope. In early November 2007, I scrambled down from a trail on the North slope of the Traverse Mountains (the foothills South of Draper, leading out to Point of The Mountain) to check out what looked like a suspect tree, only to find it wasn’t an Oak, or anything I’d ever noticed before. I took leaves and pics, and when I returned home, identified it as Alderleaf Mountain Mahogany, Cercocarpus Montanus.

Alderleaf Mountain Mahogany (AMM) occurs throughout much of the same range as Curlleaf Mountain Mahogany (CMM) and shares many similarities with it. It’s also a small, shrubby, slow-growing tree with dense wood, growing on dry, gravelly soils, with apetalous wind-pollinated flowers that produce achenes with long feathery plumes following pollination. But the leaf form and strategy is completely different. AMM leaves are oval, less than 2” long, sawtooth-edged and deciduous, and covered with fine hairs, employing the “hairy-leaf” strategy of Sagebrush as opposed to the “waxy –cuticle” strategy of Blackbrush (and CMM) to mitigate water loss in an arid climate. Though they hold their leaves much longer than neighboring Gambel Oak and Bigtooth Maple, they lose most/all of their leaves in the late Fall.

Tangent #1: At least up here they do. Down in Arizona and California they may keep more than half their leaves.

Tangent #2: Another common name for AMM is “True Mountain Mahogany.” I refuse to use this name. When I read it I had a flashback to Greek Orthodox Sunday School (man, talk about the very definition of “time-sink”…) circa 1975, when my teacher explained that, due to some weird theoretical disagreement of the nature of Christ, the Armenian Orthodox were “Nestorian Orthodox” (I probably have the term wrong) and the Greek Orthodox (us) were “True Orthodox.” Even then, I was pretty certain that our Armenian counterparts didn’t see it that way, and I’ve detested the modifier “true” for any variety, type or species of anything ever since.

Discovering AMM was a double-surprise for me; it had been years since I’d encountered a genuinely “new” tree in the Wasatch, and, while CMM occurs (albeit in bits and splotches) all over the Wasatch, I’ve yet to see AMM anywhere but the Traverse Mountains, an area I’d never really bothered to explore until my hybrid oak search.

In my last post I talked about how interesting and unique CMM is, an evergreen angiosperm tree in Northern Utah. AMM adds another dimension to the “remarkability” of Mountain Mahogany. Cercocarpus is a genus which has both deciduous and evergreen species. And it’s not a case of a Wyethia-like mis-categorization from an earlier, pre-DNA analysis age; CMM and AMM regularly hybridize when they occur together- they’re clearly in the same genus.

Tangent: Interestingly though, they can only hybridize when CMM provides the pollen and AMM the ovule. Why this is, and whether it’s an issue of timing (CMM flowers ~2 weeks earlier than AMM) or anatomy or genetics, I’ve been unable to discover.

This evergreen-vs.-deciduous variation within a genus is extremely unusual. Willows, Aspen, Cottonwoods, Palms, Maples (with 2 very rare, remote, and newly-discovered exceptions), Sycamores, Beeches, Elms- you name it- they’re all one or the other. The only other angiosperm tree genus with a similar variance in leafing strategy- at least that I’m aware of here in North America- is Quercus (Oak). And this makes me think about the relationship between Mountain Mahogany and Oak.

I mentioned in the last post that CMM only occurs sparsely and at the “margins” of the foothills, pushed there by competition from Oak (and Maple). But I have seen larger expanses- almost forests- of pure CMM in a couple of places outside the Wasatch, including the lower West slope of the Ruby Mountains in Nevada and the Lower North slope of the Raft River range, near the Utah-Idaho border. And it occurs to me now that both of these locations are outside of the range of Gambel Oak (or any other native Oak) as we saw back in May when we looked at the interesting distribution of that tree.

And this leads me to the whole “what-if” of Mountain Mahogany: if Oak hadn’t evolved, or hadn’t made it to the New World, or if Mountain Mahogany had evolved first, would Mountain Mahogany have evolved and adapted and speciated into the roles filled today by oaks? Would the Wasatch foothills be carpeted in CMM? Would “live” Mountain Mahogany ring California’s Central Valley? Would the greens of English villages be shaded by gnarled, giant, centuries-old variants of Mountain Mahogany?

Tangent: Also similar to oak, there’s an ongoing, century-long debate regarding the relationships, taxonomy and past and current hybridizations of species within Cercocarpus. (And- again like oak- the debate has been complicated/enriched by the discovery in recent decades of new Cercocarpus species down in Mexico.) A (fairly technical) synopsis of this debate can be found in the introduction to the dissertation of Brian Vanden Hauvel of the University of Texas, Austin. (Thanks Brian!)

This is all conjecture of course. But it makes me think about what trees say about how and why the world is the way it is, and how it might have turned out differently. As we’ve seen with Creosote, Joshua Trees, and Ponderosa Pine, the floral landscape of the Intermountain West (and the world) changes continually over time. I like to think Mountain Mahogany’s day is yet to come.