Hildenbrandiales is an order of crustose forms red alga which bear conceptacles and produce secondary pit-connections. They reproduce by vegetative gemma

Gemma

Gemma may refer to:In science:* Gemma , an asexual reproductive structure in plants and fungi* , a genus of clam in the family Veneridae; see amethyst gem clam...

e 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.
Some members of the order are known from freshwater rivers as well .

Systematics

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.