New features in the vegetative and reproductive morphology of Cystoclonium purpureum (Cystocloniaceae, Rhodophyta) from the North Atlantic Ocean

The seminal work of Kylin (1923, 1932, 1956) defined the family Cystocloniaceae (as the Rhodophyllidaceae) for genera having (1) a percurrent central-axial filament surrounded by a well-developed cortex; (2) procarps in which the auxiliary cell is one of the daughter cells borne immediately distal to the supporting cell of the carpogonial branch; (3) gonimoblast filaments that originate from a single initial directed either inwardly or laterally; and (4) zonately divided tetrasporangia. Most of the species currently placed in the Cystocloniaceae produce some kind of secondary gametophytic filaments in conjunction with gonimoblast development, although no such filaments have been reported in Cystoclonium purpureum or C. obtusangulum, the only two species currently recognized under Cystoclonium. Unlike the reports of previous studies, we observed an extensive system of short-celled secondary gametophytic filaments in C. purpureum that form regularly in association with gonimoblast initiation and continue their elaboration throughout gonimoblast and carposporangial development. Terminal cells of the secondary gametophytic filaments fuse with nearby fused and unfused gonimoblast cells throughout carposporophyte development. Secondary gametophytic filaments of one sort or another have been reported in nearly all other species placed in the Cystocloniaceae-Solieriaceae complex, often with linkage occurring between cells of the gonimoblast filaments and those of the secondary gametophytic filaments; however, the particular pattern of gametophyte-gonimoblast interaction described here in C. purpureum is, so far, unique among Rhodophyta.