phyl·lo·taxy \|filə|taksē, -si\noun orphyl·lo·tax·is\-ksə̇s\ (pluralphyllotax·ies \-sēz, -siz\ ; orphyllotax·es \-ˌsēz\) Etymology: New Latin phyllotaxis, from phyll- + -taxis 1.: the arrangement of leaves on a stem and in relation to one another < decussate phyllotaxy > < alternate phyllotaxy > — compare genetic spiral, orthostichy, parastichy 2.: the study of phyllotaxy and of the laws that govern it