A leaf petiole is the stalk of a leaf. There is no absolute distinction between absence and presence of the leaf stalk and for purposes of identification, a stalk less than 2mm long may be regarded as "absent".
Present (petiolate)
There is a distinct leaf stalk.
Absent (sessile)
There is no distinct leaf stalk. This is most often seen in juvenile leaves when the base of the blade may touch the stem or branchlet, or even extend around it.
