\Quin*cun"cial\, [L. quincuncialis, from quincunx.
See {Quincunx}.]
1. Having the form of a quincunx.
2. (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 [ae]stivation.
{Quincuncial phyllotaxy} (Bot.), an arrangement of five
   leaves in a spiral, each leaf two fifths of a circle from
   the next.