What kingdom is seaweed in?

Seaweeds belong to three kingdoms:

Kingdom Plantae (chlorophyte, or "green" algae seaweeds),

Kingdom Plantae (rhodophyte, or "red" algae seaweeds),

Kingdom Chromista (phaeophyte, or "brown" algae seaweeds)

Kingdom Chromista (xanthophyte, or "yellow-green" algae seaweeds), and

Kingdom Bacteria (cyanophyte, or "blue-green" algae seaweeds).

Seaweeds that belong to the Kingdom Plantae are plants; the others, strictly speaking, are not. Kombu (kelp), arame (kelp), limu moui (kelp), hijiki, mozuku, and wakame are not plants. Wikipedia places them under Kingdom Chromalveolata because they are classified as "brown" algae seaweeds. However, nori (laver), ogo (limu), and dulse are classified as "red" algae seaweeds and are placed under Kingdom Plantae.

Kingdom Protista, which includes the chlorophyll-containing, self-propelling euglenozoa, is a fourth kingdom of algae which contains no species of seaweeds.

Thomas Cavalier-Smith defined Kingdom Chromista in 1981 and redefined it as Kingdom Chromalveolata in 2005. However, in 2008, other biologists have proposed splitting Kingdom Chromalveolata into at least two smaller kingdoms and this newer version has gained increasing support.

The cancer-preventing marine polysaccharide, fucoidan, and the weight loss causing marine carotenoid, fucoxanthin, are both always plentiful in "brown" algae seaweeds, including kombu, arame, limu moui, hijiki, mozuku, and wakame. "Yellow-green" algae seaweeds, which are never sold commercially, do not contain much fucoidan or fucoxanthin, even though they are still classified as members of Kingdom Chromalveolata together with the "brown" algae seaweeds.