Fungi with segmental thallus; sexual reproduction sometimes with typical antheridia and oogonia (ascogonia) but usually much reduced.
The sexual organs - oogonia and antheridia - are borne on special portions of the thallus in cavities known as conceptacles.
Mycelium poorly developed or absent; oogonia and antheridia (without antherozoids) known in some cases; zoospores common: Chytridiaceae.
The oogonia arise on a stalk cell from the lining layer of the cavity, the contents dividing to form eight oospheres as in Fucus, four as in Ascophyllum, two as in Pelvetia, or one only as in Halidrys.
Monoblepharis has oogonia with single oospheres and antheridia developing a few amoeboid uniciliate antherozoids; these creep to the opening of the oogonium and then swim in.
Species referred on good evidence to the Charophyta are represented by a few casts of oogonia and stem fragments, found in Jurassic and Wealden beds, which bear a striking resemblance to existing species.
The antheridia and oogonia are formed at the nodes of the appendages.
Mycelium present; antheridia but no antherozoids; oogonia with one or more oospheres: Peronosporaceae, Saprolegniaceae.
In the rotting tissues branches of the older mycelium similarly swell up and form antheridia and oogonia (fig.
The Peronosporaceae reproduce themselves sexually by means of antheridia and oogonia as described in Pythium.