False spirea (Sorbaria sorbifolia, (L.) A.Braun 1860)

Identity

False spirea (Sorbaria sorbifolia (L.) A.Braun, 1860), also called Ural false spirea, is a deciduous shrub in the Rosaceae family and the type species of Sorbaria. Linnaeus originally described it as Spiraea sorbifolia in 1753. German botanist Alexander Braun transferred it to Sorbaria in 1860, the placement still accepted today. ^{1 2}

Two resemblances explain its names. The epithet sorbifolia refers to compound leaves like those of rowan (Sorbus), a more distant relative in the same family. False spiraea, an alternative spelling, refers to flower panicles resembling those of true spireas (Spiraea spp.). The leaves readily separate the genera: false spirea has many leaflets, while true spireas have simple, undivided leaves. ⁷

Recognition

Root suckers produce dense stands of upright stems, reaching 1–3 m (3–10 ft) tall with a similar spread. ^{4 7}

Alternate, pinnately compound leaves contain 13–25 toothed leaflets and measure 20–30 cm (8–12 in) overall. Their appearance recalls a fern or rowan. Separate leaflets immediately rule out true spireas (Spiraea spp.), which have simple leaves. ⁴

During June and July, hundreds of small white flowers open in upright terminal panicles 10–25 cm (4–10 in) long. Individual flowers measure about 6–8 mm (0.24–0.31 in) across. Their fragrance attracts numerous pollinating insects. ^{4 3}

Clusters of small follicles turn reddish brown as they ripen in September. They often remain on the shrub after leaf fall, extending its ornamental interest into winter. ⁷

Useful taxonomy

As the type species of Sorbaria, S. sorbifolia represents a genus of related shrubs from temperate Asia. Botanical references often discuss two close relatives alongside it: Sorbaria kirilowii (Regel) Maxim., from China and Korea, and the more southerly Sorbaria tomentosa (Lindl.) Rehder, ranging from Afghanistan to Nepal. ¹

The accepted variety Sorbaria sorbifolia var. stellipila Maxim. has star-shaped hairs on its young shoots and a more easterly range, from northeastern China through Korea to Japan. Historical synonyms, including Schizonotus sorbifolius (L.) Lindl. and the basionym Spiraea sorbifolia L., still appear in older horticultural literature. ^{1 2}

Habitat and range

For false spirea, the native range runs from Siberia and the Russian Far East to Inner Mongolia. Related populations extend into northeastern China, Korea and Japan, depending on the variety. ^{1 6}

Open woods, forest margins and riverbanks provide its natural habitat. In northern China it generally grows at 250–1,500 m (820–4,920 ft) elevation. ³

Extreme cold presents little difficulty for this shrub. Hardy to USDA zone 2, it survives in regions too cold for many temperate hedge shrubs. While dormant in winter it tolerates temperatures below −40 °C (−40 °F). ⁴

Ornamental introductions are widespread in Europe and North America. Garden escapes can establish colonies on uncultivated ground through suckering alone. Finland officially classifies it as an invasive alien species. In metropolitan France no invasive status is documented, and it remains mainly a cultivated shrub. ⁷

Life cycle and reproduction

Flower buds develop on the current season’s wood. Hard spring pruning therefore allows flowers in the following summer, unlike shrubs that bloom on the previous year’s shoots. ⁴

After insect pollination, flowers form dry follicles that release seeds in fall. Gardeners seldom use seed propagation in practice. Division of suckers and stem cuttings with a node are faster methods that preserve the original cultivar more reliably. ³

Suckering shapes the shrub’s development from its second or third year onward. New stems arising from roots expand the edge of each stand, allowing the colony to persist without depending on sexual reproduction. ⁴

Uses and risks

False spirea serves almost entirely as an ornamental shrub, in informal hedges and back-of-border plantings. Its dense, spreading roots also help stabilize riverbanks and slopes. ^{4 3}

Major toxicity has not been established for cats, dogs or horses. Raw young shoots and flowers contain traces of cyanogenic glycosides when eaten in large quantities; cooking first removes this risk. ³

Vigorous suckering is the chief gardening drawback, particularly in light soil. Regular removal of suckers is needed; unchecked, the shrub can spread into neighboring beds within a few seasons. ⁴

Serious pests and diseases rarely cause lasting damage to its foliage. This relatively undemanding plant is therefore suitable for beginner gardeners who can keep its spread in check. ⁴

Varieties, look-alikes and related plants

The compact cultivar ‘Sem’ produces colorful spring foliage that passes through yellow, bronze and red before turning green. Its panicles stand more upright than those of the typical species, and it has received the Royal Horticultural Society’s Award of Garden Merit. ⁷

True spireas (Spiraea spp.) are its main look-alikes because of their similar name and white flower panicles. One readily visible feature separates the genera: spireas have simple, undivided leaves, whereas false spirea has pinnate leaves with numerous leaflets, recalling rowan foliage. ^{7 8}

Main sources

• Plants of the World Online / Kew, Sorbaria sorbifolia (L.) A.Braun
• International Plant Names Index, Sorbaria sorbifolia (L.) A.Braun
• Plants For A Future, Sorbaria sorbifolia
• North Carolina Extension Gardener Plant Toolbox, Sorbaria sorbifolia
• ITIS, Sorbaria sorbifolia (L.) A.Braun
• USDA GRIN Taxonomy, Sorbaria sorbifolia
• Wikipedia EN, Sorbaria sorbifolia
• Wikipedia FR, Sorbaria sorbifolia