• In brown algae plant body is attached to substratum by holdfast.

what is substratum and holdfast?

Substratum is the support or a structure where an algae attaches itself. For example algae can attach itself to a rock, here rock is the substratum.

Holdfast is a rootlike or flagella like structure that is present in algae or some other plants which helps them in their attachment with substratum. Holdfast can either be rhizodial or normal type.