Conjugatae, Protococcales and Characeae are exclusively freshwater; Confervales and Siphonales are both freshwater and marine, but the latter group attains its greatest development in the sea.
Again, while Conjugatae may be shut out from Chlorophyceae as an independent group co-ordinate with them in rank, the Characeae constitute so aberrant a group that it has even been proposed to raise them as Charophyta to the dignity of a main division co-ordinate with Thallophyta.
In Characeae no fewer than four methods of vegetative reproduction have been described, and the facility with which buds and branches are in these cases detached has been adduced as an evidence of affinity with Bryophyta, which, as a class, are distinguished by their ready resort to vegetative reproduction.
Of the Characeae many are so exceedingly brittle that it is best to float them out like sea-weeds, except the prickly species, which may be carefully laid out on bibulous paper, and when dry fastened on sheets of white paper by means of gummed strips.
The Characeae among freshwater algae and the Sargassaceae among marine algae might be cited as examples.
The reproduction of Characeae is characterized by a pronounced oogamy, the reproductive organs being the most highly differentiated among Chlorophyceae.
Attached to the bottom of pools series of the Confervales, the thallus consists of filaments branched by means of rhizoids, the thallus of Characeae grows upwards by or unbranched, attached at one extremity, and growing almost means of an apical cell, giving off whorled appendages at regular wholly at the free end.
In Characeae and Muscineae they are of elongate spiral form, and consist of an elongate dense nucleus and a small quantity of - cytoplasm.
Thus simple forms included in the Heteroconteae, Chlorophyceae and Phaeophyceae show an obvious connection with the Flagellatae; the Peridineae may be regarded as a further developed branch; the Conjugatae and Diatomaceae cannot be directly connected; the origin of the Rhodophyceae is also obscure; while the Characeae are an advanced and isolated group (see ALGAE).