The area between the two lobes of this Cyclamen persicum leaf is a sinus.
In
botany, a sinus is a space or indentation between two lobes or teeth, usually on a leaf.[1] The term is also used in
mycology. For example, one of the defining characteristics of North American species in the Morchella elataclade of
morels is the presence of a sinus where the
cap attaches to the
stipe.[2]