Board Thread:Theories and Speculation/@comment-28323245-20170530200422/@comment-734582-20170601092239

Darksusanoo wrote: Given that the thing that made them was a source of Wood Release (i.e a sentient tree) The tree itself did not show any power.

Anyway, the Zetsu are likely a mixture of actual zetsu material and Hashirama DNA, which is why they're much more plantlike and have much weaker wood release.