The are in addition to the more than 500 plants in the old AR3/AR4 plants which also work with IRender nXt.
These are 'fractal' plants - meaning that detail is relative to the resolution of your image. Each plant is generated differently which automatically creates a realistic effect when using multiple instances of the same plant.
Create SketchUp components to represent IRender nXt plants. These are then automatically rendered as 'fractal' plants.