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.
These plants are also available from the 3D Warehouse: IRender Plants