There are two kinds of Sparklium flowers; a small and a bigger variant. They both contain small Sparklium Seeds but work in different ways.
The smaller one drops a Sparklium Seed for every Pikmin thrown at it. After the first Pikmin has been thrown at the flower, it starts to shrink and disappears once it's small enough.
The bigger variant contains a set amount of Sparklium Seeds. Thrown Pikmin stick to the flower and damage it over time draining its health. Once its health bar reaches zero it breaks and releases all of the Sparklium Seeds inside.
Sparklium flowers are found in most levels.