How can I tell the difference between Spiraea betulifolia var. corymbosa (an imperiled species) and Spiraea japonica (an invasive species) in the wild? They both seem to be the same size, color, habit, etc.
There are a couple ways to distinguish Spiraea betulifolia var. corymbosa from Spiraea japonica. Unfortunately, there are also some pitfalls in these distinctions! In general, our native spirea is white-flowering (occasionally lightly blushed pink), while S. japonica is typically pink to rose-red flowered. The exceptions are uncommon, but can make positive identification difficult. The leaves of S. betulifolia var. corymbosa are broadly ovate to oblong or obovate, between 4 and 7 cm long and usually less than twice as long as wide. If you are not familiar with botanical terminology think, "arrowhead shaped". Spiraea japonica leaves are lanceolate or lance-ovate, between 8 and 15 cm long and 2.5 to 5 cm wide, or typically more than twice as long as wide. Think, "spearpoint or lancehead shaped". Further, the toothed edge of Spiraea betulifolia var. corymbosa usually extends only from the leaf tip to 1/2 to 2/3 of the length of the leaf toward the base, while the toothed edge of S. japonica leaves typically extend nearly to their base. Spiraea japonica escapes from cultivation and can often be found growing in the wild. To further complicate matters, the many cultivars of S. japonica can confuse identification.
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