The Sourwood (Oxydendrum arboreum) is a deciduous tree native to the forests of the Eastern United States. It is the sole member of its genus and belongs to the Ericaceae family. Primarily found from southern Pennsylvania down to the Gulf Coastal Plain, it often thrives on the rocky, acidic slopes of the Appalachian Mountains. The tree is highly valued for its ornamental features, providing visual interest across all four seasons.
Size, Shape, and Appearance of the Trunk
The Sourwood is a small to medium-sized tree, reaching 20 to 35 feet in cultivation, though it can exceed 50 or 60 feet in its native forest environment. When young, the tree develops a narrow, pyramidal, or oval crown. This crown matures into a more rounded or irregular shape with slightly arching branches.
The trunk is usually slender and may have a slightly crooked or leaning posture, especially when growing in the understory. The bark changes as the tree ages. On mature specimens, the bark is grayish-brown or reddish-brown and develops deep vertical furrows. These furrows separate the bark into thin, scaly, and pointed ridges, often likened to alligator hide.
The Unique Foliage and Fall Color
The foliage consists of simple, alternately arranged leaves that are oblong or lanceolate in shape. These leaves are finely toothed along the edges and possess a glossy, dark green surface throughout the summer. They measure between four and eight inches in length, providing a medium texture to the canopy.
The name Sourwood refers to the leaf’s acidic taste, caused by the presence of oxalic acid. This flavor differentiates it from many other woodland species. The leaves emerge with a reddish tint in the spring before maturing to a rich green.
The Sourwood is one of the earliest trees in the eastern forest to begin its color transition. The foliage transforms into brilliant, consistent shades of scarlet, crimson, deep red, and purplish-burgundy. This spectacle often occurs by late summer or early fall, long before most surrounding trees change color.
Identifying the Flowers and Seed Capsules
The Sourwood is identified by its late-season bloom, flowering in mid-summer (late June through August), an uncommon time for a large woody plant. The small, creamy-white flowers are bell- or urn-shaped and hang in long, slender clusters called racemes or panicles.
These drooping flower clusters are highly fragrant and bear a strong resemblance to the blossoms of Lily-of-the-Valley. The nectar produced is attractive to bees, making the Sourwood a source for light-colored honey. The panicles can be quite large, sometimes reaching up to ten inches long.
The flowers give way to small, dry seed capsules that mature over the summer. These five-angled, five-valved capsules ripen from green to a silver-gray or tan color. The persistent capsules remain attached to the drooping stalks long after the leaves have fallen, providing a lace-like appearance against the winter sky.