Characteristics of Phaeophyta
The members of this division are commonly called brown algae because of dominant carotene and fucoxanthin,
The brown algae are widespread and with few exceptions all are marine. They grow attached to the rocks, shells, or coarser algae such as the kelps. In general, the brown algae flourish in colder ocean waters and on rocky coasts, where they grow attached in intertidal or littoral zone e. the members of Fucaceae and Laminariales.
They range from minute discs to thalli,100 meters or more in length.
The filamentous forms (Ectocarpus) are uniaxial, however in parenchymatous species (Fucus) the plant body may be differentiated into a holdfast through which it is attached to the substratum; a long or short stipe; and expanded leaf- like fronds that act as photosynthetic and reproductive organs.
The growth of the thallus in primitive brown algae is by an intercalary meristem at the base of a hair or filament. This type of growth-is called Trichothallic Growth, e. g., in Ectocarpus.
The cell is surrounded by distinct cell wall composed of an inner cellulose layer and an outer pectin layer. The outer layer becomes slimy or gummy due to presence of pectic compounds. The most important constituent of the cell wall is alginic acid found in the outer layer of the cell wall. It forms a colloidal substance algin which is important economically.
The reserve food is mannitol and laminarin starch.
The brown algae reproduce by vegetative, asexual and sexual means of reproduction,
The asexual reproduction is by pyriform or spindle-shaped motile zoospores with two unequal flagella. The zoospores are produced in either in one-celled unilocular sporangia or in many-celled plurilocular sporangia.
The sexual reproduction ranges from isogamy to oogamy through anisogamy.
Except for in Fucales all other members show either isomorphic or heteromorphic type of alternation of generations.