This goal of this build is to be able to continually burst down enemies as a % damage burn in teamfights. Liandry's burns 5%, combined with Rylai's slow it burns 10% of current hp PER HIT with a thornspitter. I cannot overstate how good this is on Zyra. Combined with the reduced healing from Morellonomicon, and the spell vamp from WoTa, you should have an incredible presence mid and late game.

The goal is to get Liandry's and Rylai's ASAP so you can use them to burn the enemy team's HP down in teamfights. Stay on the edges of teamfights and continually lay down plants and spells to burn as you allow your teammates to distract them.

The main downside to this build is that you may find yourself relying on teammates to deal the final blow to enemies because your damage will be mostly % of current health. You will probably end up with many near kills that your teammates grab from you simply because your skills are on cooldown.

If you have a few tanky champions on your team, you will be near unstoppable in teamfights as long as you can snare and dodge the enemies while setting up thornspitters on the sidelines of teamfights.