At this point "Plant slime" is such a saturated name that it would probably better to differentiate yours...
For instance, this sounds a lot like a
carnivorous plant! There are a lot of carnivorous plants to potentially base your slime off of - flytraps, pitcher plants, giant stinking corpse flowers...
So, what I am guessing is that this is a slime that can produce a "free" plort as long as it is in a sunny place, but will eat meat that passes by (the risk)? Does it plort if it eats meat and become "full", or does it go through meat like a Tarr?
edit: I saw it eats "future meat" and not just meat ... this makes it less dangerous, because careful management of a coop, or even not having a coop nearby at all, would totally negate its risk. In this case, I would think that this slime's plort should be valued at the Pink slime's plort or less (~7) since it's very unlikely it will deal very much damage. I would suggest it can eat ALL THE MEAT ... that would make it worth maybe ~15 coins and make it much more interesting/risky to house!
Also, can this slime move, or is it rooted to the spot? Since it can get out of its pen, I assume it moves. How does it move? Does it bounce or slide?