Living members of the Characeae
sensu lato grow in
freshwater and
brackish environments worldwide, and have large, macroscopic
thalli growing up to 120 cm long, they are branched,
multicellular, and use
chlorophyll to
photosynthesize. Their only
diploid stage in the life cycle is the unicellular
oospore. They may be called
stoneworts, because the plants can become encrusted in lime (
calcium carbonate) after some time. The "stem" is actually a central stalk consisting of giant, multinucleated
cells. They are unique in having a whorl of small branchlets at each node in the
stipe which gives them a superficial resemblance to the genus
Equisetum. In these whorls it is possible to see the phenomenon of
cytoplasmic streaming. Streaming in
Chara is the fastest recorded of any cell. Cytoplasmic streaming is caused by the microfilaments found inside the cell, as proven by the use of
cytochalasin B to stop streaming. There are about 400 extant
species worldwide, with 33 in
Britain and
Ireland according to Groves and Bullock-Webster), however Stewart and Church (1992) reduce this to 21. Characeae are the principal photosynthesizers of some of the volcanic crater lakes of
Nicaragua, and can be found in excess of 20 meters depth in some circumstances. Introduced
tilapia (
Oreochromis niloticus) consumed all the Characeae in
Lake Apoyo. The
antheridia (or globules) and
oogonia (or nucules) are protected by a layer of sterile
cells when mature; the
oogonium is oblong in shape and consists of a single egg, while the spherical antheridium is packed with threadlike cells that produce spermatia. As a result, the Characeae have the most complex structure of all green algae. ==Genera==