This key is meant to be an aid in identifying seaweeds which are relatively common on the coast of Norway. However, more than 400 taxa of marine macroalgae have been recorded from Norway, and this key only covers around 200 of these. Many rare species and most small or microscopic species are not included here, and only a few crust-forming red and brown algae are included.
How to use the key
The main division of the seaweeds is according to colour. Species of Division Chlorophyta (green seaweeds) have chlorophyll a and b and are green, species of Division Rhodophyta (red seaweeds) have chlorophyll a and some accessory pigments giving a red colour (phycoerythrin and phycocyanin), and species of Class Phaeophyceae (brown seaweeds) have chlorophyll a and c and some accessory pigments giving a brown colour (fucoxanthin). Thus, one can divide seaweeds into the three main groups according to colour. Sometimes this may still be difficult since specimens can be bleached. In such cases one can look at the basal part of the specimens, where the original colour normally can be seen. You should also know that some red seaweeds can have a brownish-red colour. If you do not reach the correct species by using the brown seaweed key, you may instead try the red seaweed key.
The key is based on grouping species according to specific characters, and some species may be intermediate and difficult to place in a group. These may appear more than one place in the key. Some species can have a very variable morphology, and in some species young specimens may look different than adult specimens. Such variations are to some degree incorporated into the key.
For each of the three main groups the key is constructed so that the number on the left-hand side normally gives two choices. Important information is often in bold. Special terms which are used in the key are defined or described in the glossary. The red algae are initially divided in three main morphological groups, and one of these must first be selected. You proceed by following the chosen number on the right-hand side. In order to see some characters a microscope is needed. If you make the right choices, you should arrive at last to the correct species or genus. For some genera systematic keys in the form of tables are made, where you have to compare your specimen with the information given in columns and rows. You should always check the name you have arrived at, by comparing the specimen to the description of the species in an illustrated algal flora. Many of the species are linked to photos from the species list, and these can be checked by opening this link.