I favour Picene. I don't think a setter would use Pine(s), and the definition is only Compound. The 'found in conifers, mostly' is wordplay, I feel - and a little bit of misdirection.
ChrisE, I agree - that it's not a good clue! I favour Picene, simply because it's a very poor setter who'd use a plural, especially just an 's' and then get solvers to remove it. PS There have been mistakes in quite a few recent EVs.
As malone says, the conifers have no bearing on the definition (the rather vague 'compound') but simply deliver either PICEA or PINES ready for truncation. If 'Compound found in conifers' were the definition, it would be an even worse clue as the 'conifers' would be performing double duty.
I agree that PINE(s) would be clumsy and unlikely, but I think that connie's original point is valid - the clue does not rule out PINENE as the answer.
Yes, ChrisE, Pinene isn't ruled out , so it's a poor clue. I also think focussing on 'compound from...' lead people astray a little. A definitive answer is always best.
Yes, looking at it from all angles, there is a possible case for either answer.
Perhaps Connie should take up her point with the crossword editor?
His./her answer might be interesting!