The way in which the individual parts in a leaf- or flower-bud are folded. (Contrasted with vernation, aestivation, the arrangement of the parts collectively.).
Late 19th century; earliest use found in Asa Gray (1810–1888), botanist. From Hellenistic Greek πτύξις fold from the stem of ancient Greek πτύσσειν to fold (from πτυχ-, πτύξ fold: see note) + -σις.