Laminaralga megafolium

From OurFoodChain

This large relative of Taxonomum extensiensus has grown to gigantic proportions as a result of intraspecific competition, being favored to grow taller to collect more sunlight than its rivals. As a result, Taxonomum megafolium has become capable of growing up to six meters above the ocean floor. It can also be found growing in areas of water less than 75 meters in depth, where its photosynthesis works most efficiently.

Taxonomum megafolium continuously grows seed pods at the side of its stem and produces food for the marine ecosystem while also providing places for smaller creatures to hide in its leaves. The seed pods loosen with age and will either drop off or become food other organisms, which isn't much of a problem as mature individuals produce many tiny seeds, which are carried off by the ocean currents to grow in favorable locations away from the parent polyph.