Hello Mahalo ..

I am not an expert either on Kelps and Seaweeds ...

This is what Harold C. Bold Professor Emeritus of Systematic Botany at the University of Texas at Austin has to say in "The Plant Kingdom" a good book by the way :

He places the "Kelps" in the Kingdom "phyta" or Kingdom plants and then into the division Phaeophyta ( Brown Algae ) the "seaweeds" I believe would fall into the Division Chlorophyta "Green Algae" ...

He defines Algae as follows : "Chlorophyllous organisms having one of the following "

1. Gametes but no specalized sex organs ( this is a charecteristic of certain unicellular Algae )
2. unicellular sex organs
3. multicelluar sex organs in which every cell forms a gamete.

Now here is the confusing part ... those or at least quite a few Algae that can be by item #1 of the above definition have been moved somewhat recently to a new kingdom Protista. These include the divisions Pyrrophyta ( Dinoflagellates ) , Euglenophyta ( Euglena ) , Chrysophyta ( Diatoms ) . These are all unicellular .. chlorophyllous and mostly autotrophs. Kelp and Seaweed are multi cellular and have been left in the plant Kingdom.

There are four other Divisions of Protista that are heterotrophs mostly... and are refered to as Protozoans.

Hope that helps a bit .. myself I spend most of my time with desert plants ... perhaps a expert in this area can chime in.

Good Day ..

Seaweed used to be in the Kingdom Protoctista but is now divided amongst two Kingdoms; the Chromista and the Eumycota. Kelp is actually a seaweed. The Divisions that Kelp fall into include: Phaeophyta, Chromophyta and Rodophyta. Phaeophyta are the brown algae, Chromophyta are the green algae and Rodophyta are the red algae.
This post is probably to late for your presentation but, if you have any other questions, just ask.