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Key to Corylus

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1 Mature involucre of the fruit 4-7 cm long, extended into a tubular beak; young twigs and petioles villous, glandless; [section Corylus, subsection Siphonochlamys]
1 Mature involucre of the fruit 1-3 cm long, the lobes flattened and laciniate; young twigs and petioles stipitate-glandular; [section Corylus, subsection Corylus]
  2 Peduncles of the staminate catkins (visible from summer until early spring) 1-5 mm long; staminate catkins in clusters of 1-2; mature involucres of nuts 1.2-2× as long as the nut; [widespread in our region, though rare or absent in parts of the deeper South]
  2 Peduncles of the staminate catkins (visible from summer until early spring) 5-12 mm long; staminate catkins in clusters of 2-4; mature involucres of nuts 0.8-1.2× as long as the nut; [rarely spread from horticultural use]