Looks familiar.
You can also use this technique to animate plants that branch. Set up a set of control path splines that provide the branch structure of the plant as it would be fully grown. Each branch will be set up essentially like Robert described above. Basically a tube with each spline ring assigned to a separate bone and constrained to the particular control path spline in a percentage pose. In addition, scale the spline ring bones very small at the zero percent end of the pose slider. At the other end scale them to 100%. That way the branch grows in thickness as it grows in length. Once you have all the branch poses set up, animate the whole set in a new overall percentage pose. Strart with the "trunk" which will define the duration of the growth animation. As the trunk passes the base of a branch, start the branch growing and complete its growth at the same time the "trunk" completes. Of course you can add layers of branching, timing each layer accordingly. Leaf clusters can be associated with their own bone. These bones do not need to be constrained to a path, but they do need to be placed where each leaf cluster will sprout. Use pose sliders to scale the leaf cluster bones. Animate the leaf clusters in the overall percentage pose as well, once each leaf cluster percentage pose is set up.
The two movies attached demonstrate the idea.
If you are a real masochist, you can build a whole tree like this:
Tree Growth Animation