You want extremely realistic 3d models of plants without a lot of work and with no experience. Don't you think something is amiss? Without experience, you're going to spend a lot of time spinning your wheels in every aspect. Without a technical director you're going to spend a lot of time just on learning how to model, render, texture, and light, before even starting on the art and biology. Extreme realism comes about by proper lighting and proper texturing. If you don't know how to light, then the most amazing plant model will look fake.
Your time is better spent with a plant generator:
http://ngplant.sourceforge.net/
Or plant libraries:
http://yorik.uncreated.net/greenhouse.html
http://www.xfrog.com/
Other misc software:
http://www.vterrain.org/Plants/plantsw.html
If you still wish to model, in general and turn a 2d image into a 3d model, most basic modeling tutorials start with this. Here are two of many. Add the image to your display ports and off you go.
http://www.blendercookie.com/2009/01/09/modeling-a-human-head-series-part-1...
http://www.blendercookie.com/2009/12/05/modeling-a-porsche-911-gt3-rs-part-...
Cory
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Cory Petkovsek
Corporate Video