I read this article yesterday in the Weekly Standard about the Swiss government who are looking into the protection of the "dignity" of plant life.
Wesley Smith brings up some good points that relate to the nature of man (what does the Bible say about man in relationship to beasts and plants?), there difference from animals, what defines humanity, etc. Here is the article in the link below:
"The Silent Scream of the Asparagus"
Psalms 8:3-9 When I look at your heavens, the work of your fingers, the moon and the stars, which you have set in place, (4) what is man that you are mindful of him, and the son of man that you care for him? (5) Yet you have made him a little lower than the heavenly beings and crowned him with glory and honor. (6) You have given him dominion over the works of your hands; you have put all things under his feet, (7) all sheep and oxen, and also the beasts of the field, (8) the birds of the heavens, and the fish of the sea, whatever passes along the paths of the seas. (9) O LORD, our Lord, how majestic is your name in all the earth!
Psalms 104:14-15 You cause the grass to grow for the livestock and plants for man to cultivate, that he may bring forth food from the earth (15) and wine to gladden the heart of man, oil to make his face shine and bread to strengthen man's heart.