What part of a seaweed holds it up?

The part of a seaweed that holds it up is called the stipe, which is similar to a stem in land plants. The stipe provides support and allows the seaweed to reach towards sunlight, while the holdfast anchors it to the substrate, such as rocks or sand, preventing it from being swept away by currents. Together, these structures help the seaweed maintain its position in the water column.