Monterey Bay Aquarium Research Institute
Marine Botany

    Morphology
    Prionitis with parts labeled

    Below: Discoid holdfast (with epiphyte). Mouse over picture for back view.

    Prionitis holdfastPrionitis lanceolata is usually dark red, and between 20-50 cm in height. It has a discoid holdfast which usually has multiple stipes growing from it. The thallus* is erect, and there is no clear distinction between the stipes* and the primary blades, which are both relatively flat. Branching is roughly dichotomous, with many irregularities. Secondary blades grow in a pinnate* fashion, with parallel rows of pinnules (secondary blades) running down the lateral margins of the primary blades.
              While the above describes a typical P. lanceolata, there are a wide variety of morphologies expressed depending on the individual's habitat. In general, the higher an individual lives, the smaller, more branched, and lighter in color it is, while the lower individuals are larger, darker, and less frequently branched. For more details on this, see Morphological Variation in the Ecology section.


    Internal Anatomy

     The cortex is the outermost layer of cells and is made up of very small, round cells arranged in rows. These cells contain the photosynthetic pigments, including phycoerythrin, which accounts for their red color. The cortex is usually 5-12 cells thick. The transitional layer is more loosely arranged, with large, round cells arranged in a more scattered fashion. The medulla is the innermost layer and is composed of elongate filaments that run longitudinally through the thallus.

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    Created by Alice Chiu, 2003. Images may be used with permission.