Monterey Bay Aquarium Research Institute
Marine Botany


The three species of Microcladia that grow on the Pacific Coast of the United
States, M. borealis, M. californica, and M. coulteri, are very similar and can be easily mistaken. However, they can be distinguished from one another by studying the physical characteristics, location, and nature of the epiphytic growth.

(Left) M. coulteri (typically 35-40 cm tall) has a regular, alternate branching pattern that is pinnate (feather-like) and distichous (arranged in two rows on opposite sides of an axis).

(Center) M. borealis (8-20 cm tall) has a regular, unilateral branching pattern, which is to say it only branches on one side of an axis, and the branching is pectinate (comb-like).

(Right) M. californica (20-25 cm tall) actually has two forms. This version has a branching pattern that is irregular, spiny, and divaricate, or widely spreading. However, it also has an alternate form that looks almost exactly like M. coulteri, with smooth, regular, alternate branching.

These size measurements should be taken with a grain of salt (no pun intended); they are highly variable. Although it is easy to tell apart M. coulteri and M. borealis due to the branching, to distinguish between M. coulteri and M. californica one must examine the carpogonia.


M. coulteri (above left and center) has involucres on its carpogonia, which are surrounding branches that hold and protect the carpogonia. M. californica (figure above right) does not have involucres on its carpogonia.


map of distribution of Microcladia

M. coulteri has been found from Vancouver Island, British Columbia, Canada, to Baja California, Mexico. M. borealis has been found from Alaska, US, to San Luis Obispo, California, US. Thus originates its "northern" name. M. californica has been found only in California, US, from San Francisco to San Diego, and only in isloated localities. It is very possible that it is not entirely a different species but a variation of M. coulteri.

M. borealis is typically found on high rocks exposed to surf. M. californica is found in the low intertidal. M. coulteri is found mostly in the midtidal to subtidal zone (10 m).


M. coulteri grows as an abundant epiphyte on large red algae, occasionally on large brown algae. M. borealis is only occasionally epiphytic. M. californica is mostly epiphytic on Egregia menzesii, commonly referred to as the feather boa. M. coulteri can also resemble Plocamium when found on the beach, but can be distinguished because Microcladia grows epiphytically and Plocamium does not.