Watermelon is a vine-like flowering plant originally from southern Africa.
It is a large, sprawling annual plant with coarse, hairy pinnately-lobed leaves and white to yellow flowers.
It is a special kind of berry with a hard rind and no internal division, botanically called a pepo.
The fruit has a smooth hard rind—usually green with dark green stripes or yellow spots.
It has a sweet, juicy interior flesh—usually deep red to pink, but sometimes orange, yellow, or white.
Watermelons have many seeds, which can be soft and white or hard and black. (source)
So can hamsters eat watermelon seeds?
They are not the best for them and should be avoided as a food.