An updated systematic catalogue of the seaweeds of the island of Ireland is presented with sources, habitats, distributions, and notes on nomenclature, taxonomy and distribution.
Included are 570 species: 303 species of Rhodophyta, 93 species of Chlorophyta, 13 species of Vaucheria, and 161 species of Phaeophyceae. Three phyla (Rhodophyta, Chlorophyta, and Ochrophyta), 11 classes (5 Rhodophyta; 4 Chlorophyta; 2 Ochrophyta), 35 orders (19 Rhodophyta; 5 Chlorophyta; 11 Ochrophyta), 91 families (50 Rhodophyta; 16 Chlorophyta; 25 Ochrophyta) are represented. English and Irish vernacular names, and sources for these are given, together with a glossary of Irish names. A list of seaweeds found in Britain but not reported from Ireland to date is given together with distributional, taxonomic, nomenclatural, and other details. A preliminary comparative conservation assessment of 334 species of rare or potentially rare species in Britain and Ireland is given (Gigartinales, Rhodophyta), and Schmitziellaceae, M.D.Guiry, D.J.Garbary & G.W.Saunders fam. nov. (Gigartinales, Rhodophyta).
Ninety-six species are known from Britain (including two varieties of species not otherwise known to occur in Britain), but not from Ireland: 53 reds, 14 greens, a single Vaucheria, and 28 browns. Twenty of these (18 reds and two browns) are considered to be adventive or potentially adventive, leaving only 76 native species that are found in Britain but not in Ireland, which results in an Irish seaweed flora that is currently about 88% of the native British seaweed flora, contrasting very favourably with a native flowering-plant flora in Ireland of about 50% of that of Britain (approximately 850 vs 1700 species). Worldwide, there are about 9500 species of seaweeds (6200 reds; 1500 greens; 1800 browns).
Thus, about 7.5% of the worlds known seaweeds occur in Ireland, which is considerable given its geographical location and range, and its relatively narrow temperature ranges and subtidal light penetration. By contrast, the native Irish flowering plant flora is, at most, 0.25% of the worlds 350-400,000 flowering plant species.
"This is a complete catalog of the marine red, green, and brown macroalgae of Ireland. Michael Guiry has done an admirable job. He is uniquely qualified to produce such a work, having consolidated information about algae worldwide for the online database www.AlgaeBase.org, and having written (F.G. Hardy & Guiry) A Check-list and Atlas of the Seaweeds of Britain and Ireland [...] and A Consensus and Bibliography of Irish Seaweeds (1978).
The catalog treats three phyla: Rhodophyta (red algae) and Chlorophyta (green algae) in kingdom Plantae, and Ochrophyta (brown algae and Vaucheria) in kingdom Chromista. The 3 phyla comprise 11 classes (respectively, 5, 4, 2), 35 orders (19, 5, 11), 91 families (50, 16, 25), and 570 species (303, 93, 174) (no stats are given for genera). Taxa are arranged taxonomically to the level of genus following AlgaeBase, with species arranged alphabetically in genera. Users not familiar with tribal classification can consult a complete index.
For each of the 570 species (and a few varieties) Guiry provides: synonymy (if pertinent to the region); type locality (for taxa described from Irish specimens); vernacular names (Irish and English); a brief statement about habitat, distribution, and rarity; and notes about nomenclature and taxonomy.
The catalog has two new taxa, both red algae (Gigartinales): Schmitziellaceae and Rhodophyllis irvineorum (Cystocloniaceae), the latter nicely depicted in a color plate. This is the only figure in the book, which needs a map. There are three appendices: an annotated list of species reported from Britain but presently unknown from Ireland; a list of Irish common names, with derivations; a list evaluating rare seaweed species in Britain and Ireland.
The catalog is preceded by four pages of historical background that introduce the influential Irish phycologists. Guiry has not included his own name, but, of course, it belongs in the list."
– Richard L. Moe, University of California, Berkeley, Taxon 62(1), February 2013, 199-200