to finish the Ghost in the Underworld's first "quest"

[Algester]

Crystalized Flowers have a chance to grow in the underworld so I suggest that you just go to these 2 areas that are crazy convenient to farm them

there are 2 flower spots on the area before the checkpoint for Ankah-Vayeh, then another check point where you beat Quos (where the campfire is if you escorted the kemonomimi NPC to the underworld)

[Moomoo]

Thank for information. i have stuck this quest

[ArcBiter]

in the big room right that leads to the last safe area in the underworld, there's a chance for corpse flowers (and therefore crystal flowers) to spawn on the left side of the room. Worth checking out as well since there's no enemies there.

[Youth Spinner]

Personally I farmed my crystallized flowers somewhere in the Giant's Nest & they seem to spawn there rather constantly. Although the problem with this spawn is that one needs to break a number of beryl barriers on the way and kill a metallum giant guarding it.