Minium parvum gen. et sp. nov., a crustose member of the Rhodymeniales (Rhodophyta)

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Abstract
Minium parvum gen. et sp. nov. exists in all stages as a crust, a growth form previously unknown in the order to which it belongs-the Rhodymeniales. While members of this order exhibit a diversity of thallus form and anatomy, only erect or decumbent types have been described heretofore. The new crustose genus comprises plants which grow epiphytically on subtidal articulated coralline algae. The vegetative crust is extremely thin, consisting of a basal layer one cell thick which bears assurgent filaments one to several cells in length. Gametophytes and tetra-sporophytes are isomorphic. In culture they alternate with one another. Reproductive structures are produced in nemathecia which arise from limited areas of the crust and which often expand laterally over the surface. Cruciately divided tetrasporangia are borne terminally among sterile filaments. Carposporangia develop in dense lobes and no tela arachnoidea is formed. While Minium unquestionably belongs to the Rhodymeniales, its position within that family is unclear.