I've toyed with the idea occasionally. The best one I came up with was a "outdoors" morph for Venus based on the Green Man -http://en.m.wikipedia.org/wiki/Green_Man. This would almost certainly be a pod, although a brainbox with a mixed solar power/ algae greenhouse life support system could work- it would be kind of huge!

Simply looking like a plant is simple enough: biosculpt yourself leaves for hair and a variation of carapace armor that looks like bark skin. You could easily get yourself looking like a sylvari or Groot with a trip to the nanovats or two. But I thought of another option when you mentioned habitat sleeving. Smartgardens. Like sleeving into a mini-habitat, this. Several habitats in the books mention the trees being modified to include processor capacity as a space-saver and design statement, and while this would limit your mobility just like any habitat, any given smartgarden is going to have a small army of bots at hand too.

Ever read Neuromancer? Flying horticulture drones include lots of sharp bits. And most agricultural chemicals are generally toxic. Hell, most polinating insects are probably mesh-rigged to the smartgarden AI/sleeved ego. Smartbees. My god.

True plants would make extremely poor morphs. The amount of energy harvested from sunlight is too low to power strong muscular movement or to power a brain capable of cognizant thought (human brains use something like 40% of our calories). It should be noted that the Whiplash is not a plant. It is a planimal from the planet Sunrise. Planimals on Sunrise that live purely through photosynthesis do not move very quickly. Top speeds are about .5 kilometers per hour. The reason that the Whiplash is able to move more quickly is because it does not survive purely on photosynthesis. It is a predatory planimal that eats other planimals, thereby gathering energy that has been concentrated. As a result a Whiplash is not capable of surviving without eating, barring the installation of a Personal Power Plant. That's not to say that you couldn't make a 'Groot' morph. For one thing, it's your game and I can't tell you how to run it. For another the Whiplash shows that the basic idea is there. All I am really saying is that if a player were to come to me asking to make a 'Groot' morph for a campaign I was running it would need to be based on planimal biochemistry rather than true plant and if they wanted to avoid eating they would have to have a PPP. Photosynthesis alone would not be enough to power them.