Spiraea alba Du Roi



CC = 9
CW = -3
MOC = 8
SRank = S1

© SRTurner

Family - Rosaceae

Habit - Shrub to 2.0 m.

Stems - Ascending or erect. Twigs reddish brown to grayish brown with prominent, small lenticels, somewhat angular, minutely hairy toward the tip when young, glabrous or nearly so at maturity.

Spiraea_alba_stem.jpg Stem and nodes.

© SRTurner

Leaves - Alternate, simple, mostly short-petiolate. Blades 3-6 cm long, somewhat stiff textured, narrowly elliptic to oblanceolate, angled or tapered at the base, angled or tapered to a sharply pointed tip, the margins finely and sharply toothed, the surfaces glabrous or nearly so.

Spiraea_alba_leaves.jpg Stem and leaves.

© SRTurner

Spiraea_alba_leaf1.jpg Leaves adaxial.

© SRTurner

Spiraea_alba_leaf2.jpg Leaf abaxial.

© SRTurner

Inflorescences - Terminal panicles of numerous flowers, longer than wide, cylindrical or ovoid to more or less pyramididal, sometimes elongate.

Spiraea_alba_inflorescence1.jpg Inflorescence.

© SRTurner

Spiraea_alba_inflorescence2.jpg Inflorescence detail.

© SRTurner

Flowers - Hypanthia 1.5-2.0 mm wide, cup-shaped, glabrous or minutely hairy. Sepals 5, 1.0-1.5 mm long, triangular, bluntly pointed at the tip. Corollas of 5 petals, not doubled, these 2.7-3.5 mm long, white. Stamens 15 to numerous, the anthers white or pink. Pistils 5 (except in doubled flowers), free. Ovary superior, glabrous, with 1 locule and 2 to several ovules. Style 1 per pistil, persistent, the stigma more or less capitate.

Spiraea_alba_sepals.jpg Hypanthia and calyces.

© SRTurner

Spiraea_alba_flowers.jpg Flowers.

© SRTurner

Fruits - Follicles 3.0-3.5 mm long, ascending, elliptic-ovate in outline, tapered to an erect beak at the tip, glabrous, tan to brown at maturity, dehiscing along the inner suture and also partially along the outer (dorsal) suture, 1-4-seeded. Seeds 1.5-2.5 mm long, narrowly ellipsoid, the surface with faint longitudinal lines or a fine network of slender ridges and quadrangular pits, yellowish to reddish brown.

Spiraea_alba_fruits.jpg Fruits.

© SRTurner

Flowering - June - August.

Habitat - Bottomland prairies, marshes, lake margins, edges of bottomland forests, ditches, fencerows, railroads, and roadsides.

Origin - Native to the U.S.

Lookalikes - None close.

Other info. - This species is uncommon in Missouri, reported from only a few widely scattered counties. Its main range is predominantly north and northeast of Missouri, and extending into much of Canada. Flowering plants are readily identified by their spikes of small white flowers which bear numerous stamens. The erect follicles of fruiting plants are also distinctive. The leaves are alternate, roughly elliptic, and somewhat stiff.

The species has long been subdivided into var. alba, nominally the form present in Missouri and the one pictured above, and var. latifolia. The latter form predominates in the eastern part of the plant's range, and differs by several subtle characters. There is significant intergradation between the two varieties and individual plants can be difficult to assign.

These plants attract butterflies and beneficial insects, and the fruits are consumed by songbirds. The straight, hollow stems have been used as pipe stems.

Photographs taken near Loda Lake, Newaygo County, MI, 8-27-2020 (SRTurner).