4. mostly marine,
Sphacelaria,Bodanella,Heribaudiella-fresh
water. Pleurocladia-fresh & marine.
most spp. in cold sea, Dictiyota, Sargassum in
atlantic sea.
some- lithophytic, submerged spp. Holdfast for
attachment. Laminaria-branched holdfast,
Fucus- discoid holdfast, grows upper region.
Sargassum, Macrocystis- middle region of sea.
Laminaria, Postelsia-benthic.
5. Thallus
most developed in algae.
branched and heterotrichous- Ectocarpus.
heterotrichy when young-Dictiyota, Laminaria
condensed and multicellular thallus with tissue
differentiation, called kelps or rockweeds.
Macrocystis-upto 60 m in length.-gaint kelp.
Necrocstis-bulb kelp, Postelsia- sea palm.
thallus- holdfast, stipe and leaf like blades. Thallus
is internally differentiated- epidermis, cortex and
medulla.
9. Cell structure:
Cell wall –gelatinous, 2parts-inner-cellulosic
outer- pectin & mucilage. Algin, fucoidin, fusin
deposited over pectin.
chromatophores- flat, parietal or discoid.
Single nucleus per cell.
Reproduction: Vegetative– mostly by fragmentation. In
Sargassum propagules are formed.
Asexual:--- by zoospores except-dictyotales And fucales.
Zoospores are formed in unilocular and plurilocular
sporangia.
unilocular – meiosis-haploid zoospores are formed.
Zoospores- biflagellated, unequal .
in Dictyota- unilocular sporangia-aplanospores-
nonmotile.
10. Sexual:
motile gametes could be isogametes or
anisogamete.they are formed in gametangia.
Fucus, Sargassum- oogamy.- antheridia, oogonia.
Ectocarpales,Spacaelariales—Isogamy
Cutelariales--- anisogamy
Dictyoales ,Laminariales- oogamy.
diploid zygote germinates and forms sporophytic
thallus. Isomorphic alternation of generation. in
Laminariales-heteromorphic.
Fucales-haplobiontic ,diplontic, monogenetic
.Ectocarpales- diplobiontic-digenetic.
Cutlariales-gametophyte dominant.
Laminariales-sporophyte dominant
