Sentence:  The species that characterize the heathland are wooly willow (Salix lanata), broadleaved willow (Salix callicorpea) and <WSD>least willow</WSD> (Salix herbacea), especially wooly willow. 
Meaning of the word marked with <WSD> tags:  (ver=180323), a tiny creeping shrub widely distributed in alpine and Arctic environments.