What rose item does Bud Squire need to evolve?

The stamen only matters on the Melloblum branch. Bud Squire can also become Thornblade.

Bud Squire is one of the Aniimo that evolve along a branching path, so it does not have one fixed next form. Each branch has its own requirements, set by the items you collect and the decisions you make in quests. The Stamen of Kubo's Rose is the item that points it toward Melloblum. If you are aiming for Thornblade instead, the stamen does not apply.

You need just one stamen, so a single find covers the whole evolution. Holding the item is not always enough on its own, though. Some evolutions have special conditions that must be met before their materials can be spent, so check that Bud Squire is otherwise ready if the stamen will not take.

You will see the names spelled more than one way: Bud Squire or Budsquire, and Melloblum or Mellowbloom. They are the same creatures and the same evolution.

Not settled: Where the Stamen of Kubo's Rose is found, and exactly what the Thornblade branch asks for instead, are not established here.