Desmarestia viridis has annual sporophytic thalli ranging 15 - 45 cm in length. Each thallus is elongate with a cylindrical stipe and discoid holdfast. When bleaching (secreting acid) it has an acrid odor and is extremely fragile. The percurrent axis has opposite cylindrical branches (0.75 - 1.5 mm wide) that are lax. The primary branches are pinnately branched (or occasionally bipinnate) and covered with short branchlets (1).

The axes have circular or oval shape (1-3 mm diameter, lower portion) with a pseudoparenchymatous structure. In the main axis, axial cells (20 - 40 µm diameter) are surrounded by colorless medulla of a fine mesh of small cells (diameter 10 -40 µm fig 2). In third order branches (diameter 200-300 µm), the axial cells (30 -40 µm diameter) are surrounded by 1-2 layers of small cells (30 -50 µm diameter) (2).

The parenchymatous tissue construction of D. viridis is associated with its trichothallic growth, where meristematic cells are localized at the base of pluriseriate filaments formed by vertical cell division (Lobban and Harrison, 1994). The bidirectional meristem is evident at the tip of any branch.

Literature cited

(1) Abbott A. I., Hollenberg G. J. 1976. Marine Algae of California. Standford University Press, Standford, CA.

(2) Belleno G. et al. 2001. First report of filamentous species of Desmarestia (Desmarestiaceae, Fucophyceae) in the lagoon of Venice (Italy, Mediterranean Sea). Botanica Marina 44: 541-545

Website, pictures and drawings created by:

Noemi Ramirez

ramirezmiss1@gmail.com

ZooBot Spring Quarter 2009

Friday Harbor Laboratories

University of Washington