Hildenbrandiales is an order of crustose forms red alga which bear conceptacles[2] and produce secondary pit-connections.[3] They reproduce by vegetative gemmae[4] as well as tetrasporangia, which are produced inside the conceptacles. The way in which the tetraspores are produced is unusual enough to justify the formation of this distinct order.[2]Some members of the order are known from freshwater rivers as well .[5]
Hildenbradiales are difficult to discriminate on morphological grounds; tetrasporangia morphology is the only vaguely reliable character, but molecular techniques have indicated a monophyletic Apophlaea within a paraphyletic Hildenbrandia, with many Hildenbrandia species being recognized as non-monophyletic.[1]