What does "quincuncial" mean?

Quincuncial: (Bot.) Having the leaves of a pentamerous calyx or corolla so imbricated that two are exterior, two are interior, and the other has one edge exterior and one interior; as, quincuncial æstivation. Quincuncial phyllotaxy (Bot.), an arrangement of five leaves in a spiral, each leaf two fifths of a circle from the next.