Spiraea arcuata

Family / Families: Rosaceae
Scientific Name(s): Spiraea arcuata Hook. f.
Institution(s): University of California Botanical Garden at Berkeley
Location(s): Berkeley, California, USA
Entry Author(s): Madeline Iseminger
Copyright Holder(s): J.G. In S.F.@Flickr aka James Gaither
Image Permissions: Please contact the copyright holder's estate for permission to use.
Photographer(s) Appreciation: Today's photographs (photo 2) of Spiraea arcuata buds and blossoms were captured by the late James Gaither (aka J.G. in S.F.@Flickr) at the University of California Botanical Garden at Berkeley.
Tags: Rosaceae, Rosales, University of California Botanical Garden at Berkeley, via Flickr

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Spiraea arcuata is a small woody shrub species native to temperate regions of eastern Asia, specifically India, Myanmar, Nepal, Bhutan, Tibet, and Yunnan (China). It can be found growing at altitudes ranging from 3000m to 4200m (~10000 to 13750 feet) in forests, rocky subalpine areas and the edges of riverbanks. There doesn’t seem to be any commonly-used English vernacular name, but arching spiraea or Himalayan spiraea have been used in a few references.

In Forests and Forestry in Nepal (Ashish Publishing House, New Delhi, 1994), S. S. Negi writes that Spiraea arcuata is one of the major constituents of dry alpine scrub vegetation in the inner valleys of Nepal. In the dry western valleys, Spiraea arcuata is associated with Berberis sp., Caragana gerardiana, Rosa sericea, and Dasiphora fruticosa as part of an open forest habitat that eventually blends into the dry alpine scrub and extends to the snow line.

Plants of Spiraea arcuata have a compact, arching shape. Depending on nutrient availability, plants can sometimes exceed heights of 1m (3 ft.) tall. New stems are coated with downy hairs. These become smooth by their first autumn. The bark of older branches is glossy, deeply furrowed, and dark reddish-brown in colour.

Corymbs of cream-coloured to deep-pink blossoms appear on short branchlets from May to June. These corymbs are densely packed, and approximately 4cm (<2 in.) wide. The five-petalled flowers possess triangular sepals and turbinate or cone-shaped hypanthia. These insect-pollinated blossoms are each 6-8mm (~.25″) across.

Fruits are dry follicles, which ripen from August to September. These follicles are exserted from the hypanthia in clusters of five. Each glabrous and lustrous follicle is a mere 2-3mm (0.1″) long.