UC specimens and range limits for Desmarestia herbacea

• 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: Species limits in the ligulate Desmarestia have been debated; herbarium records are hard to interpret. Under the names, D. ligulata, D. herbacea and D. munda, this species apparently ranges from Unalaska Island, Alaska through British Columbia, Washington, Oregon, California, and through Baja California, Mexico, and down into South America.

Status: Specimens of this species from Bamfield, British Columbia, Canada, San Juan Island, Washington, San Francisco, and Santa Barbara, California, have been analyzed with SSU, ITS (nuclear), cox1 (mitochondrial), and psaA, rbcL (plastid) markers (Yang et al. 2014). These authors concluded that width of blade varies, and consider wide-bladed D. munda and D. latissima to be conspecific with D. herbacea.

Habitat: Low intertidal to subtidal, where it can be common in kelp forests and urchin-dominated or disturbed areas

Life History: An alternation of heteromorphic generations, with large foliose sporophytes and minute filamentous dioecious gametophytes

Search Sequences in GenBank

Desmarestia Lamouroux 1813

Sporangial thalli perennial, elongate, remarkable in the field owing to large amounts of acids produced when plants are collected, bleaching nearby plants and producing an acrid odor. Holdfast stout, disklike, producing single erect axis, this soon forming opposite or alternate branchlets according to species, rarely unbranched. Axes and branches slightly to markedly compressed; some species remaining finely branched throughout, others becoming foliose. In Calif., a seasonal occurrence of hairs at margins of branches. Thalli containing unangia rarely collected in Calif.

Despite large size of some species (to 3 m long), internal structural features and cell modifications not as elaborate as in order Laminariales. Center of thallus with several axial strands having thick walls and surrounded by thick cortex of colorless cells, interspersed by colorless rhizoids. Surface layer of cells containing many lenticular chloroplasts, without pyrenoids. Tufts of hairs in which the intercalary meristem is found are terminal on branches. In older thalli, some transverse and longitudinal walls frequently pitted; cytoplasmic threads traversing the pits probable.

Desmarestia ligulata (Lightf.) Lamour.

Fucus ligulatus Lightfoot 1777: 946. Desmarestia ligulata (Lightf.) Lamouroux 1813: 45; A. Chapman 1972: 1 (incl. synonymy). Fucus herbaceus Turner 1808: 77. D. herbacea (Turn.) Lamour. 1813: 45; Smith 1944: 121. D. munda Setchell & Gardner 1924b: 7. D. jordanii Gardner 1940: 269. D. linearis Smith 1944: 120. D. mexicana Dawson 1944a: 236.

Thalli annual, some perhaps perennial, to 8 m tall, the holdfast lobed or smooth, conical or flattened, 2-4 cm diam.; stipe flattened; axes usually broader at base and tapering upward or broad throughout, (0.5)1-2.5 cm broad; midrib usually prominent in mature plants, with opposite veins leading to branches; second-, third-, or rarely fourth-order branches appearing stipitate from these veins, the "stipes" becoming spines with loss of higher order of branching; trichothallic filaments forming dense marginal fringe in some forms, quickly formed and early deciduous in others.

Any set of characters chosen for taxonomic purposes shows an overlap in the young thalli of D. herbacea and D. munda, whereas mature thalli show quite distinct habits. When examined in large series and compared with specimens from the N. Atlantic, these taxa do not remain distinct. In our own flora, the taxon previously known as D. linearis (which resembles the earlier D. jordanii) is known only from subtidal collections; in the same way, the supposedly distinct D. mexicana is separated geographically from other populations. Thus, although it is possible to select out certain specimens as distinct, such distinctions blur with increased numbers.

Desmarestia ligulata var. ligulata

Margins of young plants densely fringed with hairs, these deciduous with age; thalli compressed, less than 1 cm to 2-3 cm broad at base when young, to 1 m wide in some forms when mature, with several orders of branching.

Locally abundant, saxicolous or on wood, low intertidal to subtidal (15 m), Alaska to S. America; in Calif., from Humboldt Co. to La Jolla.

Widely distributed in N. Hemisphere. Type locality: Scotland.

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: Chapman's treatment, followed by Abbott & Hollenberg (1976), has not held up in the molecular era. D. munda, D. mexicana, D. latissima are synonyms of D. herbacea. D. ligulata is probably also in California; see Similar Species.