The twisted, curly stems will be the best identification feature. Salix matsudana ‘Tortuosa’ called corkscrew willow, also has twisted stems; but its leaves and buds look very different from Corylus avellana ‘Contorta’. Once you see both plants you will not get them confused!
Karren Wcisel, TreeTopics.com
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Betulaceae, Corylus avellana, contorta, deciduous, shrub