Again, among Siphonales only one family (Vaucheriaceae)has reached the stage of oogamy, although an incipient heterogamy is said to occur in two other families (Codiaceae, Bryoosidaceae).
Among Confervales there is no family in which sexual reproduction - isogamy or oogamy - is not known to occur among some of the component species, and as many as four families (Cylindrocapsaceae, Sphaeropleaceae, Oedogoniaceae, Coleochaetaceae) are oogamous.
Of the small family of the Tilopteridaceae our knowledge is as yet inadequate, but they probably present the only case of pronounced oogamy among Phaeosporeae.;.They are filamentous forms, exhibiting, however, a tendency to division in more than one plane, even in the vegetative parts.
Reproduction by conjugation is also known as isogamy, by fertilization as oogamy.
The four species - Ectocarpus siliculosus, Giffordia secunda, Cutleria multifida and Haplospora globosa - may be taken to represent, within the Phaeosporeae, successive steps in the advance from isogamy to oogamy.
The reproduction of Characeae is characterized by a pronounced oogamy, the reproductive organs being the most highly differentiated among Chlorophyceae.