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 sexual organs - oogonia and antheridia - are borne on special portions of the thallus in cavities known as conceptacles.
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.
In Dictyota the oospheres arise singly in oogonia, crowded together in sori on the surface of the female plant.
The discovery by Brebner of the specific identity of Haplospora globosa and Scaphospora speciosa marks an important step in the advance of our knowledge of the group. Three kinds of reproductive organs are known: first, sporangia, which each give rise to a single tetra-, or multi-nucleate non-motile, probably asexual spore; second, plurilocular sporangia, which are probably antheridia, generating antherozoids; and third, sporangia, which are probably oogonia, giving rise to single uninucleate non-motile oospheres.