Letting the spore settle: what is seaweed?

Seaweed has started to feature a fair bit in discussions about new super-foods, as diversifying our palate, as seasoning, as food for free or just bringing back something that was once a feature of many a coastal inhabitants diet. Let us face it, this is exactly what Slate Islands Seaweed is about, look it is in the name! Sea Veg would have possibly carried fewer connotations of something olive-brown covering the rocks and clinging to us as we go for a swim in the sea but even then this would not do justice to this incredibly diverse group of macro-algae. For what we group together as seaweed are far more diverse by nature than our common edible terrestrial plants.

So, what are seaweeds?

This is a good question, one that is in some ways simple to answer as well as quite hard to get across. Seaweeds do not fall nicely as a single group, as in, they are not in evolutionary terms or phylogenetically similar. They are a heterogeneous or polyphyletic. In fact they are not even all considered plants. Yes they are all photosynthetic (i.e. use the sun as a primary source of energy) organisms and broadly all eukaryotic (i.e. not bacteria) but that is about as far as it goes. Ok so generally they kind of look similar, the, whatever they should be called, do all consist of a holdfast (can resemble a root system, merely the anchor of the organism to the substrat), a stipe (looks like a stem, but is not hollow and does not have a phloem and xylem system) and a thallus (stop being rude, it is the highly characteristic blade or leaf like structure).  Classically they were broadly grouped by their visible pigment as red, green and brown macro-algae (water living plant, as it were), or rhodophyta, chlorophyta and phaeophyta. This difference kind of still holds true, each group produces very different pigments used in photosynthesis, different storage and protective (against predation and dessication) compounds as well as have very distinct life cycles. Cell structure and even cellular connections differ markedly between the groups. All this has lead to determining the red and green (rhodophycae and chlorophycae) belong in the plant kingdom where as the brown (phaeophycae) belong in the Kingdom of Chromista, which include some fungi, water moulds and the phytoplankton group of diatoms.

Or to put it another way, this makes brown seaweeds as different from red and green seaweeds as animals are from red and green seaweeds. Yeah, they are that similar.

So classification wise, red seaweeds are Kingdom Plantae, Phylum Rhodophycae; green seaweeds are Kingdom Plantae, Phylum Chlorophycae and brown seaweeds are Kingdom Chromista, Phylum Ochrophyta, class Phaeophycae.

What does this mean?

Well in a way it makes my job a bit more interesting and possibly the company name redundant (oops). It means I look at that seashore in a whole new light. But what it means is that these organisms only superficially interact with their environment in the same way. It means that each group will have very different compounds (secondary metabolites as they should strictly be called) for say coping with oxidative stress from being left out in the sun, for dealing with UV radiation for even just undergoing photosynthesis. It kind of means we may need to look at the browns in a different light, maybe as sea mushrooms or something. It does mean we need to stop clumping them in altogether and start re-evaluating how we use them, what role they play in the inter-tidal and shallow sub-littoral marine system, which species we should focus on, open up the EU table to more than 22 recognised edible species (that is probably later on).

Maybe to start with, we really should stop calling them all seaweed.  Or maybe restrict that to one group, the greens maybe? The reds become sea beets or sea carrots (they do have a fair number of carotenoids)? The browns can stay as sea shrooms.

I am now digressing and speculating. What I think it means is we do need to diversify our use, in the same way we have a diverse use of different terrestrial plants, mushrooms and other fungi. We need to diversify our tastes, so that if someone says “I don’t like seaweed” we can say “OK which one? Have you tried this?”. After all, I don’t like peas much but doesn’t stop me loving broccoli.   Though this does beg the question: does eating sea spaghetti count as one of my 5-a day if it isn’t a plant?