|Flowers and foliage|
Sieb. ex Blume
Spiraea thunbergii (common names : baby's breath spirea, Thunberg spirea; Japanese common name : yuki-yanagi) is a small, long-lived shrub with thin, flexible stems. It is native to Japan and China. It is also a popular landscape shrub in southeastern U.S.
The flowers are white, borne in early spring (late March to early April) and late fall. It reaches a height of 1.5-1.8 meter and is about as wide. The alternate, simple, almost linear leaves are semideciduous.
This plant produces phytotoxic cis-cinnamoyl glucosides and cis-cinnamic acid  The plant-growth inhibition characteristics can be used against diverse species as lettuce (Lactuca saliva), pigweed (Amaranthus retroflexus), red clover (Trifolium pratense), timothy (Phleum pratense), and bok choy (Brassica rapa var chinensis). The characteristics of these natural chemicals indicate a potential role of cis-cinnamic acid and its glucosides as allelochemicals (chemicals, released from plants, that cause an interaction between plants and other living organisms) for use as plant growth regulators and weed suppression in agricultural fields and in natural ecosystems. 
This species forms an interspecific hybrid with Spiraea japonica L. fil. 
In the horticultural trade one can obtain several varieties of Spiraea thunbergii, such as 'Mt Fuji' (white flowers), 'Ogon' (bright yellow-green leaves and white flowers), 'Mellow yellow' and 'Fugino pink'