Utah Native Plants for the Landscape: Mountain Mahogany
The mountain mahoganies are a group of shrubs or small trees common across much of the western United States. The name ‘mountain mahogany’ is thought to come simply from the color of the heartwood which does resemble the appearance of the tropical wood, though they are not related. There are two main species of mountain mahogany in the intermountain region, Cercocarpus montanus (true or alderleaf mountain mahogany) and C. ledifolius (curl-leaf mountain mahogany), and a number of varieties (Fig. 1). The taxonomy tends to be complex in part because both the species and their varieties freely hybridize with each other.
True mountain mahogany is a deciduous to semi-evergreen shrub with oval leaves with serrated edges on the distal half. It is rarely over 13 feet in height. It is actinorhizal, meaning the roots can be colonized by the nitrogen fixing bacteria Frankia. The ability to fix nitrogen makes it a valuable plant in sustainable landscaping because it does not require the use of supplemental nitrogen fertilizers. The fruit is characterized by a large cork-screw shaped plumose style that gives the plant a fuzzy appearance from mid to late summer. True mountain mahogany is rejuvenated by fire with new shoots coming from the base of the plant.
While curl-leaf mountain mahogany is closely related to true mountain mahogany and has the same type of flower and the typical corkscrew shaped plume, its thick leaves are evergreen, have smooth edges, and curl down on the outside edges exposing the top and concealing the bottom (Fig. 2). curl-leaf mountain mahogany is significantly larger than true mountain mahogany and can grow to the size of a small tree. It often has multiple stems and is susceptible to serious damage and mortality by fire. It has a very deep root system, and as with true mountain mahogany, it is also actinorhizal. curl-leaf mountain mahogany is not a particularly competitive plant and performs better in plantings where it is protected from competition by grasses or other herbaceous plants. In the wild, it is a desirable browse for deer and elk, and provides shelter and food for birds. Due to its adaptation to browsing, it can be heavily pruned in a landscape situation to retain a small size or modify it to landscape requirements. It is also relatively free of diseases and insects.
Within the curl-leaf mountain mahogany species, C. ledifolius var. intricatus (or little-leaf mountain mahogany) is one of the most interesting. In the wild it is found in very harsh, rocky, dry sites. It is tolerant to high temperatures, minimal water, and is found primarily in Utah, Nevada, and Arizona. It is smaller than the species (less than 8 feet) and stays shrub-sized rather than approaching the small tree category. It also has a very dense and intricate branching pattern, with the stems being a significant part of its appearance and adding a rather coarse textured feel (Fig. 3). The leaves are evergreen, much narrower than those of curl-leaf mountain mahogany, and are so strongly curled under as to appear almost like a needle.
curl-leaf mountain mahogany has great potential as a landscape plant. Its ability to fix nitrogen, relative resistance to disease and insects, and drought tolerance make it an excellent choice for sustainable water conserving landscaping. Its versatility is also enhanced by being tolerant to pruning and even coppicing. It can be high-headed into a tree form or kept in a shrub form with multiple stems. While it does not have a showy floral display, the corkscrew-shaped plume is a very unique and attractive attribute. On the downside, it must be protected from competition, especially during establishment. It should not be considered fire tolerant, nor should it be used in landscape situations where it might add to potential structural damage from fire. The little-leaf mountain mahogany variety arguably has greater potential for use as a landscape shrub than does the species. It is smaller and more manageable than curl-leaf mountain mahogany, and can be found in a number of forms such as procumbent, oval, or fastigiate (Fig. 4). It can be used in the landscape as a specimen plant or as a border or hedge. It is very drought tolerant and can play a significant role in water conserving landscapes. It should be grown in well-drained soils with care not to over-irrigate.
Both curl-leaf mountain mahogany and little-leaf mountain mahogany are easily propagated by seed and produced in the nursery. If unique selections are to be used in the landscaping industry, it is essential that methods of vegetative propagation be developed to retain those characteristics. While there are genetic differences in the ability to root, as a rule they can also be propagated by cuttings (Fig. 5). Both curl-leaf and little-leaf mountain mahogany can also be propagated vegetatively through the use of mound layering. They are easily grown in containers or the field and can be transplanted either bareroot (when dormant) or from containers.
Mee, W., J. Barnes, R. Kjelgren, R. Sutton, T. Cerny, and C. Johnson. 2003. Water wise: native plants for intermountain landscapes. Utah State University Press. pp. 17-19.
R.M. Lanner. 1984. Trees of the Great Basin: a natural history. University of Nevada Press. pp. 179-180.
Shaw, N.L., S.B. Monsen, and R. Stevens. 2004. Rosaceous Shrubs. In: Monsen, S.B., R. Stevens, and N.L. Shaw., comps. 2004. Restoring western ranges and wildlands. Gen. Tech. Rep. RMRS-GTR-136-vol-2. Fort Collins, CO; USDA For. Serv. Rocky Mtn Res. Station pp. 545-552.
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