the immortal red crust

  FHL Marine Botany  ::::::::::::::::::::::::::::::   Taxonomy | Habitat | Morphology | Life History | Ecology | Overgrowth




[L.2] Diagram of a conceptacle in Hildenbrandia (adapted from Dethier 1987).



The life history of Hildenbrandia is mysterious. Unlike many other encrusting algae, Hildenbrandia is not an alternate life cycle stage of an erect alga. It is isomorphic, cycling from crust to crust (1, 2, 3). However, no sexual reproduction has been documented in this genus, not even in culture studies; the only observed form of propagation is via tetraspores (2, 3). As such, we can guess that most Hildenbrandia individuals we come across are haploid, but even these reproduce via tetraspores (i.e., mitotic tetrasporogenesis) (4).




As in the Corallinaceae, the tetrasporangia of Hildenbrandia develop in conceptacles. But conceptacle formation in Hildenbrandia is unusual, and it has been used to place Hildenbrandiaceae into its own order (3, 5). The tetrasporangia of coralline algae are derived from intercalary cells, which then form into conceptacles as surface cells are sloughed off. In contrast, the tetrasporangia of Hildenbrandia spp. are derived from surface cells, which "erode" the perithallus to form a conceptacle (5). This process of tetrasporogensis is reported to occur year round (6).




The anatomy of Hildenbrandia's conceptacles is debated. In addition to tetrasporangia, there are more ambiguous filamentous structures that have been identified by different scientists as paraphyses, trichogynes (suggesting sexual reproduction?), the walls of emptied tetrasporangia, and also fungal hyphae (3).

  1. Bertness, M.B. et al. 1983. Snail grazing and the abundance of algal crusts on a sheltered New England rocky beach. Journal of Experimental Marine Biology and Ecology 71:2, pp. 147 - 164.
  2. Dethier, M. N. 1987. The distribution and reproductive phenology of intertidal fleshy crustose algae in Washington. Canadian Journal of Botany 65:9, pp. 1838 - 1850.
  3. Pueschel, C.M. 1988. Ultrastructural observations of tetrasporangia and conceptacles in Hildenbrandia (Rhoodophyta, Hildenbrandiales). European Journal of Phycology 17:3, pp. 333 - 341.
  4. For more information about tetrasporangia forming via mitosis, see Cole, K.M. & Sheath, R.G. (eds.). 1990. Biology of the Red Algae. Cambridge. pp. 32 - 34 and 359 - 362.
  5. Pueschel, C.M. & Cole, K.M. 1982. Rhodophycean pit plugs: an ultrastructural survey with taxonomic implications. American Journal of Botany 69:5, pp. 703 - 720.
  6. Unfortunately, no conceptacles or tetrasporangia were found on the samples I collected on San Juan Island, but references (2) and (3) have excellent pictures for both H. rubra and H. occidentalis.