UC specimens and range limits for Ulva lactuca

• Blue markers: specimen records
• Yellow marker: type locality, if present
• Red markers: endpoints of range from literature

View map from the Consortium of Pacific Northwest Herbaria

Notes: Ranging from Alaska to central California. Very few herbarium specimens have been confirmed by DNA sequence, but see photographs of WTU specimens.

Status: Most Ulva species are difficult to identify to species. This species is more common in the north than in California, and is difficult to differentiate from other broad-bladed species. Photographs of WTU specimens have been confirmed by DNA sequences (Hayden & Waaland 2004).

Habitat: Mid-low intertidal, subtidal

Life History: Alternation of isomorphic phases, with the sporophyte producing quadriflagellate zoospores and unisexual gametophytes producing biflagellate anisogametes; male and female gametes capable of parthenogenetic development (Tanner 1986; Chihara 1969a; Smith 1947).

Search Sequences in GenBank

Illustration from DeCew's Guide to the Seaweeds of British Columbia, Washington, Oregon, and Northern California

Ulva Linnaeus 1753

Thalli membranous blades, broadly expanded, distromatic, mostly without hollow margins. Blades annual, mostly without stipe; rhizoidal processes from multinucleate lower cells extending downward between blade margins forming usually perennial holdfast. Cells of blade mostly uninucleate. Chloroplast single, laminate or cup-shaped, usually on outer face of cell, with 1 to several pyrenoids. Sporangial and gametangial thalli usually morphologically similar; fertile areas marginal or terminal; zoospores quadriflagellate. Gametes biflagellate, isogamous or anisogamous. Zygote germinating without dormant period.

"Gomontia polyrhiza," which may be a stage in the life history of species of Ulva, is described on p. 120.

Ulva lactuca L.

Linnaeus 1753: 1163; Setchell & Gardner 1920b: 265; Smith 1944: 45; Papenfuss 1960: 304.

Blades light to medium green, with discoid attachment, soft and lubricous, sometimes deeply incised, the margins plane or ruffled, to 18 cm tall, sometimes broader than long, 35-40 µm thick at margins, 45-90 µm in middle; cells irregularly arranged, 10-20 µm diam., quadrate to slightly elongate anticlinally; chloroplast cup-shaped, filling outer third of cell, with 1-3 pyrenoids; gametes conspicuously anisogamous; thalli probably monoecious.

Occasional on rocks or other algae, upper intertidal to subtidal, sometimes floating on mudflats in lagoons, Bering Sea to Chile; in Calif., known from Humboldt Co. to San Diego Co. Widely distributed. Type locality: N. Europe.

Field experience on the Monterey Peninsula has demonstrated that this species is far less abundant than herbarium material would indicate, and that U. lactuca is probably misidentified more frequently than any other species of Ulva. Size of cells in section, and shape of cells, are far more critical for the identification of this species than for that of other species in the flora. Ulva expansa and U. lobata are frequently identified as U. lactuca, but have cells often twice the thickness of those of this species, and are more vertically elongate. Both U. expansa and U. lobata are far more abundant than U. lactuca.

Excerpt from Abbott, I. A., & Hollenberg, G. J. (1976). Marine algae of California. Stanford University Press, Stanford, California. xii [xiii] + 827 pp., 701 figs.

Notes: Some specimens are expanded blades with perforations, growing in subtidal and intertidal zones and formerly known as Ulva fenestrata (e.g., Gabrielson et al. 2006). Small, upper intertidal specimens are difficult to distinguish from U. californica.