Board Thread:Naruto Discussions/@comment-32617252-20170909181532/@comment-734582-20170913080321

UntappedRage wrote: The only one who could tell was Kaguya, with her Byakugan. Hagoromo also could tell with his Rinnegan. But yea, the point still stands. even Madara with his Rinnegan couldn't tell that Naruto was Hashirama's Reincarnation brother.

Besides, i've pointed out before that Naruto's hand is likely made of (imitation-)Zetsu material, since that isn't prone to overwhelming the user when they're low on chakra (unlike hashirama cells with Danzo for instance, or all the dozens of failed experiments from Orochimaru). Considering Spiral Zetsu could even boost Yamato, it's likely that strong wood release is his "thing" whereas the cloned zetsu seemed to be of a weaker, spying variant.

So Naruto has few of hashi's cells (likely) and we've seen that you need quite a bit to have a wood release.