What is the functional group for polysaccharides?

The two important functional groups in most polysaccharides are the hydroxyl group and the acetal group.

Starch is a typical polysaccharide. Its partial structure is

There are many OH groups (alcohol or hydroxyl groups).

There is also the glycosidic linkage that joins C-1 of one ring to C-4 of the next ring.

It looks like an ether.

But it isn't an ether, because it has two O atoms attached to C-1 of the glucose unit. It is an acetal.

The general structure of an acetal is

It has a C, an H, and two OR groups directly attached to the central C atom.

So a polysaccharide contains both hydroxyl and acetal functional groups.