New material collected from the Rhynie Chert Bed (Siegenian age) has revealednewfilamentous and unicellular algae. Two of the filamentous forms and one palmelloid form are described. Filamentous and unicellular algae are particularly common in a white kind of chert not previously reported and which is interpreted as having been formed by thein situsilicification of a silicate‐rich pond.Some rhizoid‐nodes ofPalaeonitella cranii(Kidston&Lang) Pia and a possible rhizoid‐borne pro‐embryo are also described and compared with similar structures in living Cha