Originally posted by Siegfried67:

Spear and mace gameplay are completely different, so i see no reason not to have a Plains Tier spear.

The problem is taht Porcupine does split prierce and blunt damage, which makes it the best weapon against the Lox, but it's crap on Yagluth and the BM sword is better for Fulings. A Plains tier spear would outperform it against Lox and render the weapon irrelevant.
Btw for Growths the best weapon is the Iron Mace.