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Q. Who is Mr. Smarty Plants?

A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Tuesday - April 12, 2005

From: Pittsburgh, PA
Region: Mid-Atlantic
Topic: Plant Identification
Title: Differentiating between Spiraea betulifolia and Spiraea japonica
Answered by: Joe Marcus

QUESTION:

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.

ANSWER:

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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