By Jan63
United Kingdom 
Can anyone tell me what this is? Under the leaf it looked like roots had formed, it only appeared on 1plant...I've never seen it before.
14 Jul, 2016
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Its caused by a gall wasp, and this particular one is commonly known as Robin's Pincushion, occurs usually on wild roses, info here
http://www.cumbriawildlifetrust.org.uk/species/robins-pincushion
14 Jul, 2016