You have a problem.
If you intend to do above-average renderings, you'll want to investigate Artlantis and the fast-rendering [some seasonally changing] plant libraries they sell.
When exporting the Archicad file, you simply make a layer with Archicad plant material that can be turned off in Artlantis and superior material substituted.
Many users generate complex, botanically convincing trees using Onyx Tree Pro and export them with simplified geometry to Archicad.
I have enjoyed trees from the Hoshino Residential Library for many years, but while they look very plant-like, they are also rather geometric - not 'random'. For schematic design, not rendering.
Dwight Atkinson