Phyllotaxis

Crisscrossing spirals of Aloe polyphylla

Phylotaxy or phylotaxis is the mode of arrangement of leaves on the stem of a plant (from Ancient Greek <span title="Lua error in package.lua at line 80: module 'Module:Language/data/ISO 639 override' not found. transliteration" class="Unicode" style="white-space:normal; text-decoration: none">phýllon "leaf" and <span title="Lua error in package.lua at line 80: module 'Module:Language/data/ISO 639 override' not found. transliteration" class="Unicode" style="white-space:normal; text-decoration: none">táxis "arrangement").

Phyllotaxy has a function: it avoids over-crowding of leaves, and exposes the leaves to the most sunlight for photosynthesis. The four main types of phyllotaxy are alternate, opposite, ternate and whorled.

Phyllotaxis Media

Veronicastrum virginicum has whorls of leaves separated by long internodes.
A Lithops species, showing its decussate growth in which a single pair of leaves is replaced at a time, leaving just one live active pair of leaves as the old pair withers
A decussate leaf pattern
Decussate phyllotaxis of Crassula rupestris