The American Smoketree

Photo by Andrew Ward licensed under CC BY-NC 2.0

I am a sucker for smoketrees (Cotinus spp.). These members of the cashew family (Anacardiaceae) are a common sight around my town and really put on a dazzling show from late spring through fall. When I finally got around to putting a name to these trees, I was a little bit bummed to realize that all of the specimens in town are representatives of the Eurasian species, Cotinus coggygria, but it didn’t take me long to find out that North America has it’s own fascinating representative of the genus.

The American smoketree (Cotinus obovatus) is not terribly common in the wild or cultivation. Today, it exhibits a suffuse distribution through parts of southern North America, with disjunct populations occurring along the Ozark Plateau of Arkansas and Missouri, the Arkansas River in eastern Oklahoma, the Cumberland Plateau in northeastern Alabama, Tennessee, and Georgia, and the Edwards Plateau in west-central Texas. The major habitat feature that unites these populations is soil. All of them are said to grow on rocky, calcareous soils prone to drought.

Photo by Megan Hansen licensed under CC BY-SA 2.0

It is an interesting distribution to say the least. I haven’t found too much in the way of an explanation for why the American smoketree is limited to calcareous soils in the wild. Apparently it is fairly adaptable to different soil types in cultivation. Perhaps competition with other species limits this tree to harsh conditions. It isn’t a big species by most standards. The American smoketree generally produces multiple stems and only occasionally reaches heights of 30 feet (9 meters) or more in most circumstances. One phrase that gets repeated with some frequency is that the American smoketree likely represents a relictual species.

Though hard to prove without ample fossil evidence, it seems many experts believe that American smoketrees (and the genus Cotinus in general) were far more common and widespread in the past than they are today. Indeed, the fossil remains of a species named Cotinus cretaceus (sometimes C. cretacea) were found in Alaska and date back to the late Cretaceous. Given that the American smoketree’s closest living relatives are found throughout parts of Europe and Asia, such evidence suggests that this genus spread into North America during a period when land bridges connected the two continents and has since been reduced to scattered populations of this single North American species.

Photo by Andrey Zharkikh licensed under CC BY 2.0

European colonization of North America did not help the American smoketree either. American smoketree sap can be processed into a yellow dye, which was highly coveted during the American Civil War. Its rot-resistant wood was also widely used for fence posts. At least one source I found indicated that the tree was cut to near extirpation in many areas for these reasons. Luckily today, with harvesting pressures largely a thing of the past, the American smoketree has rebounded enough that it is currently considered a species of least concern.

The American smoketree has also benefited from some minor popularity in cultivation. Like its Eurasian cousins, the appeal of this species comes from its colorful foliage, wonderfully flaky bark, and billowy inflorescences. Its egg-shaped leaves emerge in spring and are silky and pink. As spring gives way to summer, the leaves gradually turn a pleasing shade of blueish-green. Come fall, the leaves paint the landscape in bright red until they are shed. Late spring is generally the blooming time for American smoketree.

Photo by geneva_wirth licensed under CC BY-NC 2.0

Photo by peganum licensed under CC BY-SA 2.0

Its tiny, inconspicuous flowers are borne on large, branching panicles. Each panicle is covered in tiny hairs that apparently continue to grow well after the flowers have been pollinated. This is where the name smoketree comes from. From afar, a tree covered in panicles looks as if it is billowing dense clouds of smoke from its canopy. The whole spectacle is stunning to say the least and I just wish this species was more popular than its cousins.

All in all, the American smoketree is a truly interesting species. From its fractured distribution and curious history to its status as an obscure native tree in cultivation, there are a lot of reasons to love this species. Though related to plants like poison ivy (Toxicodendron spp.), smoketrees only rarely cause dermatitis in particularly susceptible individuals. I hope I get the chance to see an American smoketree in the wild some day.

Further Reading: [1] [2] [3] [4] [5]

Dwarf Sumac: North America's Rarest Rhus

James Henderson, Golden Delight Honey, Bugwood.org.

In honor of my conversation with Anacardiaceae specialist, Dr. Susan Pell, I wanted to dedicate some time to looking at a member of this family that is in desperate need of more attention. I would like you to meet the dwarf sumac (Rhus michauxii). Found only in a few scattered locations throughout the Coastal Plain and Piedmont regions of southeastern North America, this small tree is growing increasingly rare.

Dwarf sumac is a small species, with most individuals maxing out around 1 - 3 feet (30.5 – 91 cm) in height. It produces compound fuzzy leaves with wonderfully serrated leaflets. It flowers throughout early and mid-summer, with individuals producing an upright inflorescence that is characteristic of what one might expect from the genus Rhus. Dwarf sumac is dioecious, meaning individual plants produce either male or female flowers. Also, like many of its cousins, dwarf sumac is highly clonal, sending out runners in all directions that grow into clones of the original. The end result of this habit is large populations comprised of a single genetic individual producing only one type of flower.

Current range of dwarf sumac (Rhus michauxii). Green indicates native presence in state, Yellow indicates present in county but rare, and Orange indicates historical occurrence that has since been extirpated. [SOURCE]

Research indicates that the pygmy sumac was likely never wide spread or common throughout its range. Its dependence on specific soil conditions (namely sandy or rocky, basic soils) and just the right amount of disturbance mean it is pretty picky as to where it can thrive. However, humans have pushed this species far beyond natural tolerances. A combination of agriculture, development, and fire sequestration have all but eliminated most of its historical occurrences.

Today, the remaining dwarf sumac populations are few and far between. Its habit of clonal spread complicates matters even more because remaining populations are largely comprised of clonal offshoots of single individuals that are either male or female, making sexual reproduction almost non-existent in most cases. Also, aside from outright destruction, a lack of fire has also been disastrous for the species. Dwarf sumac requires fairly open habitat to thrive and without regular fires, it is readily out-competed by surrounding vegetation.

A female infructescence. Photo by Alan Cressler

Luckily, dwarf sumac has gotten enough attention to earn it protected status as a federally listed endangered species. However, this doesn’t mean all is well in dwarf sumac land. Lack of funding and overall interest in this species means monitoring of existing populations is infrequent and often done on a volunteer basis. At least one study pointed out that some of the few remaining populations have only been monitored once, which means it is anyone’s guess as to their current status or whether they still exist at all. Some studies also indicate that dwarf sumac is capable of hybridizing with related species such as whinged sumac (Rhus copallinum).

Another complicating factor is that some populations occur in some surprisingly rundown places that can make conservation difficult. Because dwarf sumac relies on disturbance to keep competing vegetation at bay, some populations now exist along highway rights-of way, roadsides, and along the edges of artificially maintained clearings. While this is good news for current population numbers, ensuring that these populations are looked after and maintained is a difficult task when interests outside of conservation are involved.

Some of the best work being done to protect this species involves propagation and restoration. Though still limited in its scope and success, out-planting into new location in addition to augmenting existing populations offers hope of at least slowing dwarf sumac decline in the wild. Special attention has been given to planting genetically distinct male and female plants into existing clonal populations in hopes of increasing pollination and seed set. Though it is too early to count these few attempts as true successes, they do offer a glimmer of hope. Other conservation attempts involve protecting what little habitat remains for this species and encouraging better land management via prescribed burns and invasive species removal.

The future for dwarf sumac remains uncertain, but that doesn’t mean all hope is lost. With more attention and research, this species just may be saved from total destruction. The plight of species like the dwarf sumac serve as an important reminder of why both habitat conservation and restoration are so important for slowing biodiversity loss.

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3]James Henderson, Golden Delight Honey, Bugwood.org.