Phaeophyta - Brown Algae-3

Morphological Diversity

Their Size Range is from 1mm -> 50m

Except for Biflagellate Gametes, there are NO Unicellular Forms.

They range in shape from simple filaments to large complex organisms.

Sphacelaria

Macrocystis_mid_depthHue300.jpg (108746 bytes)

Macrocystis is very large

They have the Greatest Degree of Morphological Complexity among the Algae.

Growth Forms

The Unicellular Filaments of some Phaeophytes have Intercalary Growth. This means that cells other than Apical Cells divide and contribute to the overall growth of the Thallus. Growth can thus occur in any part of the Thallus.

In the simplest case the divisions occur in only the Transverse Plane and thus, contribute to the length of the filament. However, longitudinal divisions can occur periodically and produce branches.

Longitudinal divisions by many contiguous cells of the Primary Axis can also produce a partial sheet-like morphology. This is called a Corticated Thallus.

Young Thallus showing Simple Branching along the Primary Uniseriate Axis

Mature Corticated Thallus which shows the effects of Longitudinal divisions along the Primary Axial Filament.

In some cases, a prostrate system of branches produces erect filaments. This is called Heterotrichy (Other Hairs) and is common in the Phaeophyta. Encrusting forms exhibit Heterotrichy. These are composed of short filaments which adhere laterally & attach to the substrate.

Leathesia is Heterotrichous but its small surface filaments can't be seen at this magnification.	A Encrusting Heterotrichous Growth Form (Ralphsia)
Section through an encrusting species (Petalonia). A compact, highly branched assembly of filaments is attached to the substrate. Short unbranched filaments are produced towards the outer surface. This is an example of Heterotrichy!