There are three main types of reproduction found in alage
1) Vegetative reproduction
2) Asexual reproduction and
3) Sexual reproduction
1) Vegetative reproduction
Vegetative reproduction takes place by fragmentation, each fragment grow into a new algal plant body.
2) Asexual reproduction
Some specialized structures formed by a plant which directly develop into new individuals are considered as mode of asexual reproduction. It takes place by variety of ways.
a) Zoospore formation: Zoospores are motile asexual spores produced by large number of algae belonging to Chlorophyceae and few of Phaeophyceae. In Chlorophyceae, zoospores are formed by Chlamydomonas etc. In Phaeophyceae, zoospores are formed by Ectocarpus. The zoospores found in Ectocarpus bears two laterally placed unequal flagella, one of them is tinsel type and other whiplash type.
b) Aplanospores: These are non motile thin walled spores formed in Ulothrix, Microspora and Vaucheria. The aplanospores formed in Chlorella are called autospores.
c) Hypnospores: These are thick walled spores formed under adverse environmental conditions. In Chlorophyceae, the aplanospores secrete thick wall and form hypnospores, as found in Chlamydomonas.
d) Akinetes: Akinetes is the direct modification of a vegetative cell. In the formation of akinete, the entire protoplast of the vegetative cell rounds off and the original parent cell wall becomes considerably thickened. In Chlorophyceae, akinetes are formed Ulothrix and other algae.
e) Endospores: These are formed in certain members of Cyanophyceae such in Dermocarpa. Endospores are non motile and produced by division of protoplasts.
f) Monospores: Monospores are produced singly in the monosporangium, as in some members of Rhodophyceae.
g) Carpospores: These are produced by division of zygote while within the carposporangium as in certain members of Rhodophyceae.
h) Tetraspores: These non motile spores are characteristically produced in Rhodophyceae in the special structure called tetra sporangia, as in polysiphonia.
2) Sexual reproduction
A wide range of sexuality is found in algae different types of gametes are formed they are following.
Isogamous: If male and female gametes have same shape and size are known as Isogamous.
Anisogamous: If the male and female gametes are morphologically different such gametes are known as Anisogamous.
Oogamous: In this the female gametes is comparatively large, inactive and non motile where as male gamete is smaller, active and motile.