Taxonomy and Nomenclature of Plocamium pacificum (Linnaeus) Kylin 1925

Taxonomy:

 

Division:	Rhodophyta	Very ancient division, as can be seen on the Tree of Life
Class:	Rhodophyceae	There is only one class in the Division
Subclass:	Florideophyceae	Only other subclass is Bangiophyceae
Order:	Gigartinales (Plocamiales)	Although some still consider Plocamium to belong to the Gigartinales (Sze 1998), there is molecular evidence for the Plocamiales, (Saunders & Kraft 1994.)
Family:	Plocamiaceae	Silva 1980b, showed that Thamnophoraceae decaisne 1330, was a taxonomic synonym and Plocamiaceae was retained.
Genus:	Plocamium	Only other Genus is Plocamiocolax, which is parasitic on Plocamium. (Goff 1997)
Species:	Plocamium pacificum Kylin 1925	Currently there are 47 species of Plocamium distributed around the globe. Other species on Pacific coast of America: Plocamium violaceum Farlow 1877 Plocamium tenue Kylin 1925 Plocamium oregonium Doty 1947

Nomenclatural History:

For centuries one of the four species of Plocamium that grows on the pacific coast of Northern America was referred to as Plocamium cartilagineum, which inhabits most of Europe and the Indian Ocean. However, in 1925 Kylin collected a specimen of what should have been P. cartilagineum from San Juan Island, Washington. After analyzing that specimen he pointed out that the eastern Pacific version is more robust, has a more cartilaginous appearance, has a rounder cross section and has more branching in the tetrasporangia. Based on these observations Kylin assigned the new species name P. pacificum to what is today commonly referred to as P. cartilagineum. The latter species still exists, but not on the western coast of northern America. This was confirmed by leading phycologist Paul Silva of the Jepson Herbarium.

Plocamium cartilagineum has undergone many name changes over the years. Linnaeus, the same Linnaeus who created the scientific binomial naming system, first named the species Fucus cartilagineus in 1753. Fucus, however, was a catchall genus used to describe most large fleshy algae. The name has evolved through a pattern of confusing personal opinions, faulty identifications and more recently, through molecular research.

The table below summarizes the many names that have been used to refer to P. cartilagineum. It is because P. pacificum is often referred to as P. cartilagineum that the entire nomenclatural history of P. cartilagineum is also given below. Plocamium pacificum was referred to as Plocamium angustum J. (Linnaeus) Agardh 1863 until the Eastern Pacific population was renamed P. pacificum (Linnaeus) Kylin 1925. P. angustum went through a series of name changes, and in 1967 Dixon renamed it P. cartilagineum. This name included changing P. pacificum by including the Eastern Pacific in the distribution of P. cartilagineum. However, there are physical characteristics that have been reported to separate the two species and P. cartilagineum is not found in the Eastern Pacific. Even though P. pacificum is the correct name for the species appearing on America's northwestern coast, it is still often referred to as P. cartilagineum.
 
 
 

Species:	Identified by:	Year:	Notes, if any:
Fucus cartilagineus	Linnaeus	1753	Type (original reference specimen) allegedly from "Oceano australiore," but probably actually from Northern Europe
Conferva rubra	Hudson	1762	Illegitimate synonym for Plocamium cartilagineum, according to Silva
Fucus plocamium	Gmelin	1768
Fucus coccineus	Hudson	1778	Illegitimate name
Plocamium vulgare	Lamouroux	1813
Plocamium coccineum	Lyngbye	1819	Illegitimate name, but was used extensively in the literature
Plocamium pussillum	Sonder	1845	Taxonomic synonym
Plocamium brachiocarpum	Kützing	1849	Taxonomic synonym
Plocamium cruciferum	Harvey	1855	Taxonomic synonym
Plocamium angustum	J. Agardh	1863	Taxonomic synonym
Plocamium leptophyllum	V. May	1965	Taxonomic synonym
Plocamium cartilagineum	Dixon	1967	Plocamium cartilagineum is in Indian Ocean and Europe - NOT the Pacific Americas.
Plocamium pacificum	Kylin	1925	Plocamium pacificum is on Pacific coast of northern America only. Type (original reference specimen) collected from San Juan Island, Washington.

Table compiled, in part, from information from the Jepson Herbarium.

Note:

Taxonomic Synonym means that someone believes two different specimens are actually the same species.

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