Know Your Natives – American Snowbell

American snowbell or storax (Styrax americanus) of the Storax (Styracaceae) family is a large deciduous shrub with bell-shaped snowy-white flowers. The genus name is the ancient Greek name for a European species, Styrax officinalis. The specific epithet refers to the native range of the species. In the U.S., it occurs from Illinois and Virginia south to the Atlantic and Gulf Coasts. In Arkansas, it is found across the state except for the Highlands of the northwestern one-third of the state. An understory species in nature, it prefers hydric soils in and along borders of swamps, boggy areas and drainages. In its natural semi-shaded habitat, it is a broad shrub with an open structure.

A deciduous, non-suckering, multi-stemmed shrub with thin, smooth, finely textured bark, storax grows to about 15 feet. Older stems are finely mottled in gray and pale green while previous year’s twigs are finely lined in tans and browns. Twigs of new growth are light to medium green.

Photo 1: American snowbell is an understory shrub that favors wet soils. Main stems tend to be straight and ascending. Photo – May 12.
Photo 2: Main stems join near ground level. Bark is thin and smooth.

New twigs grow from terminal and lateral buds (buds are without protective scales) along previous year’s twigs. New twigs are covered with very short and dense woolly pubescence. The terminal bud and several distal lateral buds develop vigorous new leafy twigs with no or few terminal flowers. Lateral buds occur in pairs, one above the other. Proximal buds develop into less dominant leafy twigs that bear one to several individual flowers in leaf axils. While distal twigs may be 6 inches long, proximal twigs are shorter, to 3 inches long. These tend to die out within a year or two so that the interior of a shrub tends to be open. Twigs are slightly zigzagged.

Leaves are elliptic to oval with larger elliptic leaves occurring toward the twig apex and smaller oval leaves occurring toward the twig base. Large leaves may be 3 inches long, including a ⅛- to ¼-inch-long petiole, and 1½ inches wide. Small leaves, to as small as ¼ inch long, have the same proportions, with petioles remaining about ⅛ inch long. Pubescence of twigs decreases onto petioles and underside of leaf blades. New leaves have a medium green upper surface that darkens with age. The lower surface is paler.

Venation is prominent, with four to six widely spaced, off-set lateral veins. Secondary veins arch toward blade margins, but blend with tertiary veins a short distance from margins. Upper veins are recessed, lower veins expressed.  Tertiary veins form a reticulate pattern. Leaf margins are distinctive, bearing tiny soft-tipped teeth.

Photo 3: The divide between current-year twig and previous-year twig is indicated by the red arrow, the site of the previous year’s terminal bud. Inflorescences are borne on lateral twigs growing from lateral buds along previous year’s twig. Upper side of twigs shown.

Pendulous, bell-shaped (campanulate) flowers, blooming in May, are evenly distributed around the shrub, with flower-density greater in brighter light. Most flowers grow from leaf axils (axillary) sited along new lateral twigs, one or two flowers per leaf. Additionally, racemes of two to five flowers grow directly from the tip of lateral twigs (terminal flowers).

Photo 4: Underside of same twigs shown in Photo 3. Leaf axils of lateral twigs bear one or two individual flowers, while short racemes of flowers terminate the same twigs. Note differences in leaf color and venation between this photo and Photo 3.

Flowers are showy, and the shrubs are often used ornamentally. The corolla is sympetalous, with 5 snowy-white, recurved lobes, measuring about ¼ inch broad. The 8-10 white stamens form a compact group around the pistil. The slender white style extends just beyond the stamens. Stamens are free-standing in their upper two-thirds and fused to one another at their base. The ring of stamens is also fused to the base of the corolla tube. Anthers are elongate and vertically aligned with the filaments. They dehisce on their inward side to release yellow pollen. The style is tipped with a slightly green flat stigma. The corolla tube is set in a short, cuplike calyx rimmed with five short teeth.  Ovaries are superior. With the passing of anthesis, the corolla, with the stamen group intact, separates from the calyx, exposing the ovary. Pedicels are about ¼ inch long.

Photo 5: Display shows: #1) a flower bud (over-draped by a discarded corolla), #2) flowers at anthesis, #3) corolla and stamens separating from calyx, and #4) ovary within a calyx, with style still attached.

In mid- to late September, fertilized flowers produce globose, ¼-inch-long drupes that each contain a single nutlet surrounded by a thin but tough shell. Fruits are secured by pedicel and calyx until maturity. Exterior of fruit, calyx and pedicel are light yellowish green with a fine dense pubescence. As fruit develops, the shell splits along three lines from the base, while remaining connected at the tip. At maturity, the shell  becomes yellowish tan, ultimately opening fully and releasing a dark brown, hard globose nutlet.

Photo 6: Twig with leaves and fruit, the fruit before dehiscence held by the calyx and pedicel. Open fruit: shell dehisced from base to apex and globose nutlet fallen out.

American snowbell would be attractive in a garden or natural area with consistently wet soil and sufficient space for a large shrub. It can do well in a partially to fully sunny site. Sunnier sites will produce a denser shrub that has a greater floral display.

Big-leaf snowbell (Styrax grandifolius), a shrub to small tree, also occurs in Arkansas. American snowbell can be distinguished from big-leaf snowbell by its preference for hydric sites, its smaller, more-elliptic leaves, and fewer flowers per terminal raceme.

Article and photographs by ANPS member Sid Vogelpohl

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