In botany, phyllotaxis or phyllotaxy is the arrangement of leaves on a plant stem (from Ancient Greek phýllon "leaf" and táxis "arrangement").
Describing website silo architecture in this way might be a bit obscure, but it is meant to imply that a website that is well designed using Website Silo Architecture has a higher potential to become self-organizing and rank higher for 100% more keywords using up to 90% fewer links than the competition. In order to accomplish this Russell recommends using Vertical Online Market Analysis in order to confirm the top level silo landing pages and therefore the branches (articles) and leafs (keywords) of the website. Of course this is usually determined by the most profitable keywords as determine by Krakken, Theme Zoom's proprietary natural language processing tool.
For more information on this topic in terms of biology, please visit the Max Planck Institute for Developmental Biology.