What is "parastichy"

Parastichy \Pa*ras"ti*chy\, n. [Pref. para- + Gr. sti`chos a row.] (Bot.) A secondary spiral in phyllotaxy, as one of the evident spirals in a pine cone.

n. (context botany English) A secondary spiral of leaf

Parastichy, in phyllotaxy, is the (invisible) spiral line of the pattern of the areoles on some plants, such as cactuses and pinecones. These spirals involve the insertion of a single primordium. They have been described as an effect of the human eye and the way it connects "nearest points" on certain spiral patterns.