Polysiphonia: one of the reds from the largest of the red families, Rhodomelaceae

Note the vegative branches below and the mature cystocarp containing carposporangia below it. The 2N carpospores form the tetrasporophyte stage which them produces tetraspores which form the gametophytic stage.. 3 life stages instead of the 'norma'l 2.

In the second major grouping, the Corallinaceae, we note in the photo below a special area referred to as the geniculum
which allows flexing in this otherwise rigid calcarous plant