Absolutely the answer for Mac altho it was said at ACUE last year something called "Botanica" [or something - as I remember] was superior on PC. Look around.
Onyx comes with a great library of real - ie: non archigeometric but accurate organic trees, and you can edit any aspect of the tree or build from scratch.
The attachment shows one of their "Fantastic" trees - what you'd use with ArchiCAD's new Hobbitown library objects - the toadstool being one of them.
To export to ArchiCAD is a bit tricky - the trunk/branches must be imported independant of the foliage as DXF [later combined as one object in ArchiCAD but this is how you keep the materials separately designated] or by using an intermediate file format with other renderers - see file list in the attachment.
The DXF onyx export process can be filtered to eliminate excess polygons. Leaves can be flattened and enlarged - twigs eliminated - all to get the poly count down. All controlled on a sliding scale.
To increase apparent complexity of larger leaf surfaces is easy in LightWorks because of the new eroded transparency material control that make leaf surfaces dapple.
Dwight Atkinson