Parastichy
Parastichy is a spiral line that connects successive elements in a plant’s phyllotactic arrangement, such as leaves around a stem or seeds in a flowering head. A parastichy traces a path through points that lie roughly along a spiral around the axis, and in many plants two main families of parastichies can be observed in roughly perpendicular directions, producing a characteristic grid-like pattern on the surface.
In many phyllotactic patterns the numbers of parastichies in these two families are consecutive Fibonacci numbers.
Parastichies are typically not exact mathematical spirals but are well approximated by logarithmic spirals that trace
The term parastichy derives from Greek para, meaning beside or alongside, and stichos, meaning row or line.