Ulvaria obscura var. blyttii (Areschoug) Bliding 1969: 574

Ulvaria obscura var. blyttii (Areschoug) Bliding 1969: 574


Type locality: Coast of Finmark, Norway (as Ulva blyttii) (Scagel 1966).

Etymology: Adjective (Latin), dark, shady, indistinct (Stearn 1973).

Common name: Dark sea lettuce. Like apples, Ulvaria contains the polyphenol oxidase enzyme, which turns it dark green under air exposure (Druehl 1936). This aspect is crucial in distinguishing Ulvaria from other bladed green seaweeds (Druehl 1936). When dried, it can stain paper with a brown color (Taylor 1937). Besides polyphenol oxidase enzyme, Ulvaria also produces dopamine, an adrenaline-like compound (Druehl 1936).


1. Classification:

Chlorophyta: Ulvophyceae: Ulvales: Ulvaceae: Ulvaria.


2. Identification:

Ulvaria obscura var. blyttii is dark green in color and forms very broad, irregular and delicate blades that can reach up 30 cm in length (Taylor 1937; Druehl, 1936) (Fig 1). Ulvaria is very similar to Ulva (sea lettuce), but the former occurs mostly lower on the beach. Ulvaria and blade-forming Ulva spp. are often confused in the field, by the number of cell layers  (Druehl 1936). Ulva exhibits a distromatic (two cell layers) blade, while Ulvaria is monostromatic (one cell layer).


Cross-section of Ulvaria obscura


3. Distribution:

Worldwide, this species is found in the Arctic, Europe, North America and Japan (Guiry & Guiry 2013). Its distribution along Pacific Coast of America is from Southern British Columbia to Northern Washington (Scagel 1966). This species can be found in pools in the upper littoral zone, but also occurs in the littoral and sublittoral regions, over rocks, pebbles or attached to other algae and to shells (Burrows 1987).


The regional distribution was assessed through herbarium specimens deposited in the FHL Herbarium. Vouchers are commonly labeled as Monostroma fuscum and Monostroma fusca. The species was firstly reported in the area in 1904, and is reported for the following sites/dates:

SuciaIsland, 1904;

KanakaBay, San JuanIsland, 1907;

Puget Sound, 1921;

BrownIsland, San JuanIsland, 1921 and 1962;

FridayHarborLabsBay, 1962;

Turn Point, San Juan Islands, 1962;

Minnesota Reef, San JuanIsland, 1964;

Mar Vista, San JuanIsland, 1964 and 1982;

North of Lonesome Cove, San JuanIsland, 1968;


4. Vouchers:

During the development of this page, one herbarium specimen was prepared. The alga was collected on Reuben Tarte, on June 21th, attached to rocky substratum. The specimen was collected and determined by Carolina Azevedo.


5. Research Notes:

Ulvaria is the updated name for a group of green algae that possess a leaf-like monostromatic thallus. Previously, they were known as Monostroma, an illegitimate name for these algae (Burrows 1987). Ulvaria species have thalli that are formed by upwelling of a vesicle from a prostrate disc, in which the vesicle splits open or divides into a uniseriate filament, again forming a vesicle which splits open or forms the monostromatic frond directly (Burrows 1987).

Regarding taxonomic characteristics, this species is characterized by thalli that are 60-72 μm thick, 15-20 μm broad, and with quadrate cells. A single barrel-shaped chloroplast with 1 to 8 pyrenoids is present (Scagel 1966; Burrows 1987). The holdfast is reinforced by rhizoids arising from cells above the holdfast. Cells of the lamina are mostly unordered with occasional formations of rows (Burrows 1987). The species studied here, Ulvaria obscura var. blyttii, has isomorphic alternation of generations, with foliose gametophytic and sporophytic life phases (Burrows 1987), consistent with its placement in the order Ulvales.


6. Literature Cited:

Bliding, C. 1969. A critical survey of European taxa in Ulvales, Part II. Ulva, Ulvaria, Monostroma, Kornmannia. Botaniska Notiser 121: 535-629, 47 figs.


Burrows, E. W. 1987. Seaweeds of the British Isles. NaturalHistoryMuseum Publications, London.


Druehl, L. D. 1936. Pacific Seaweeds. Harbour Publishing, MadeiraPark.


Guiry, M. D. and Guiry, G. M. 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 30 June 2013.


Scagel, R. F. 1966. Marine Algae of British Columbia and Northern Washington, Part I: Chlorophyceae (Green Algae). NationalMuseum of Canada. Bulletin No. 207. Biological Series No. 74. 257p.


Stearn, W. T. 1973. Botanical Latin. History, grammar, syntax, terminology and vocabulary. Timber Press, Portland.


Taylor, W. R. 1937. Marine Algae of The Northeastern Coast of NorthAmerica. Ann ArborUniversity of Michigan Press, Norwood.


7. Links to additional resources:




8. Page Authors & Affiliations:

Carolina Angélica Araújo de Azevedo.

Universidade de São Paulo, Instituto de Biociências, Departamento de Botânica, Laboratório de Algas Marinhas. São Paulo, Brazil.