Algae
From Memory Alpha, the free Star Trek reference.
Algae are photosynthetic, eukaryotic organisms classified as protista.
Kelp buds are a type of Human seafood. They are produced by kelp, an algae, which can be found in Earth's oceans and is sometimes informally referred to as "seaweed" by Humans. (TNG: "The Wounded")
The uniforms worn by Starfleet personnel in the 23rd century were made from xenylon, a material which was made from processing a type of algae. Since the Starfleet uniforms were synthesized from an organic form of matter, they contracted along with the crew exposed to the shrinking ray. (TAS: "The Terratin Incident")
In 2269, the crew of the USS Enterprise was on a mission to the planet Argo, where they had to collect seawater and algae specimens. (TAS: "The Ambergris Element")
Algae is among the sea foliage the Aquans harvest for what they term as "edibles". (TAS: "The Ambergris Element")
In 2373 during their attempt to teach an infant Changeling how to shapeshift, Doctor Mora suggested that he and Odo expose the Changeling to simple lifeforms such as algae, fungus and then invertebrates. (DS9: "The Begotten")
Slug-o-Cola is a Ferengi beverage that contains 43% live algae. (DS9: "Profit and Lace")
The Breen fed Ezri Dax and Worf a diet of algae paste while they were being held as prisoners aboard a Breen warship. (DS9: "'Til Death Do Us Part")
