Exposed blades hanging down

Variety in the Intertidal Reds

Since I laid my hands on the new edition of Druehl and Clarkston’s Pacific Seaweeds, I’ve spent hours letting it guide me through the diversity of west coast seaweeds. It’s a celebration of morphological variety. Chapters on green, red, and brown seaweeds are organized by morphological theme- crusts, cylinders, simple blades, branched, bushy, feather-like, and more.

When it comes to algal variety, you’re going to have a tough time topping the reds. So, inspired by Druel and Clarkston, I’m illustrating some of their common morphological themes (you can find more in Pacific Seaweeds or on your nearest exposed rocky shore).

These images are from the northern Oregon coast where all the types shown are common. Common, doesn’t mean easy to identify. For that, I’ve come across a new helper, the Seaweed Sorter app. It poses questions about color and morphology to help sort your seaweed. I tried it out on one of the examples in this post. Here’s what I was asked:

Is it brown or yellow in color?
Is it red or pink in color?
Does it branch?
Does the branching pattern have a main central axis with branches coming off the sides?
Is it calcified?
Is it entirely round in cross-section?
Are veins apparent, when blades are held up to the light?
Is it epiphytic, growing on another plant?

A few simple questions and photos for comparison was all it took to identify Prionitis (bottom left on my collage). At least I think it’s Prionitis. Identifying seaweeds is tricky. If I blow a call, I’m not going to blame the app.

If you have a thirst for reds, you’ll find more color and morphology variations on my Red Algae page.


Druehl, L. D. and B. E. Clarkston. 2016. Pacific Seaweeds: A Guide To Common Seaweeds of the Pacific Coast. 2nd ed. Harbour Publishing Co.

Variations on a Theme


  1. Very cool. I think I may have to buy this app. I’ve always like dichotomous keys, and this makes it easy enough to help teach my kids how to go about looking through one.

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