Clethras in North Carolina

There are two species of Clethra (summersweet or sweet pepperbush) native to North Carolina that are often confused and this page is supposed to provide some guidance on identification. Their ranges actually do not overlap, so for plants found growing wild, it is safe to assume that any Clethra found growing in the mountains (or more rarely in the foothills) is C. acuminata, whereas any Clethra found in the coastal plain (or more rarely in the Piedmont) is C. alnifolia. (For plants in cultivation, this neat separation of course doesn't hold true. Most plants found in public plantings and gardens are cultivars of C. alnifolia.)

Growth habit, leaves, and bark can be diagnostic when trying to distinguish between the two species based on morphology. C. acuminata is a large shrub to small tree 10-12 ft big on average, whereas C. alnifolia is a thicket-forming shrub usually no taller than 6 ft. Older stems of C. acuminata have reddish and peeling bark ('cinnamon bark' giving it one of its common names, cinnamon clethra), wheres the stems of C. alnifolia are brown-gray with thin and smooth bark. The leaf shapes are what give these plants their scientific names. C. acuminata has pointed leaves with concave sides along the tip (acuminate) and finely toothed margins, whereas C. alnifolia leaves resemble alder (Alnus) leaves and are blunt or pointed with straight sides and serrated margins that do not extent all the way to the base. If the plants are in bloom, it is possible to use flower scent as an indicator as well. C. alnifolia has a sweet fragrance that is hard to miss (hence its common name summersweet), while C. acuminata has a more spicy fragrance that is barely noticeable.

The NC range map above was colored in using data from the Vascular Plants of North Carolina website. The plant drawings are from the USDA PLANTS database and not copyrighted (original source: Britton & Brown: An illustrated flora of the northern United States, published 1913). They are scaled to each other - C. acuminata has indeed larger leaves compared to C. alnifolia. For another comparison of the leaves of the different Clethras and similar species, also see the Native Plants of the Carolinas and Georgia website. (C. tomentosa listed on that page is now mostly treated as a variety or synonym of C. alnifolia and not a separate species.)

Posted on November 10, 2019 05:25 PM by annkatrinrose annkatrinrose


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