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Name derivation:

Dumontia = Named for Georges Louis Marie Dumont de Courset, a French botanist and horticulturist

contorta= L. contortus: twisted, entangled

common names: worm weed or Dumont’s weed


Dumontia  J.V.Lamouroux  1813;  3 of 33 species descriptions are currently accepted taxonomically (Guiry and Guiry 2014).



algae have erect fronds, 10-25 (-60) cm tall, with tendril-like axes, usually clustered, dull red or dull yellow when old, and attached by a shield-shaped holdfast.  Erect axes degenerate during summer and crustose bases regenerate next spring.  Axes are twisted or contorted, simple or often irregularly-alternately (1-2 times) branched, solid near bases and young branches, while older axes are hollow, inflated or compressed, and 12 -26 mm in diam.  Medulla has loose filaments in mucilage with outer ones producing short radial rows of cortical cells.  Tetrasporangia cruciate; gametophytes are dioecious.


Similar genera:

Cystoclonium purpureum is superficially similar but has different anatomical features.


An introduced very common species, particularly during winter-late spring annual, eroding to perennial axes in the fall. On rocks in tide pools and to 10 m, and with a variable morphology.




Guiry, M.D., and G.M. Guiry  2013.  AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.  http://www.algaebase.org; searched on 16 January 2013.

Kilar, J. A. and A. C. Mathieson. 1978. Ecological studies of the annual red alga Dumontia incrassata (O. F. Müller) Lamouroux. Bot. Mar. 21: 423-437.

Taylor, W. R.  1957. Marine Algae of the Northeastern Coast of North America. Revised edition. Univ. Michigan Press., Ann Arbor, ix + 509 pp.( as D. incrassata)