A Lamina in the algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

 is a generally flattened structure which typically forms the principal bulk of macroscopic plants. It is often developed into specialised organs such as flotation bladders and reproductive organs.

The lamina is typically an expansion of the stipe

Stipe (botany)

In botany, a stipe is a stalk that supports some other structure. The precise meaning is different depending on which taxonomic group is being described....

 which in term is attached to the substrate by the holdfast

Holdfast

A holdfast is a root-like structure that anchors aquatic sessile organisms, such as seaweed, other sessile algae, stalked crinoids, benthic cnidarians, and sponges, to the substrate. ...

.