Hildenbrandia

Hildenbrandia is a genus of thalloid red alga comprising 26 species. The slow-growing, non-mineralized thalli take a crustose form.[1] Hildenbrandia reproduces by means of conceptacles and produces tetraspores.

Hildenbrandia
The darker red alga encrusting this rock fragment is H. crouaniorum
SEM of a H. rivularis gemma. Scale bar: 50 μm
Scientific classification
(unranked): Archaeplastida
Division: Rhodophyta
Class: Florideophyceae
Order: Hildenbrandiales
Family: Hildenbrandiaceae
Genus: Hildenbrandia
Nardo, 1834

Morphology

Hildenbrandia cells are around 3–5 μm in diameter and the filaments are around 50–75 μm in height.[2]

The thallus comprises two layers; the hypothallus, which attaches to the rock, and the perithallus, a pseudoparenchymous layer comprising vertical filaments, which unlike coralline red algae is not further differentiated.[3][4]

Growth

Hildenbrandia comprises orderly layers of vertical oblong cells with thick vegetative cell walls, occasionally connected by secondary pit connections with pit plugs in the septal pores.[5] It grows at its margins, away from the centre, and is able to quickly repair any gaps arising by regenerating from a basal layer of cells.[6] As plants become more mature, they become multi-layered and strongly pigmented near their centres, whilst their single-layered margins begin to grow more slowly.[6] Multi-layered areas may develop in the margins; these will detach and float away as gemmae to form new colonies, leaving a single layer of cells beneath them once they separate from the host plant.[6]

Newly settled gemmae form rhizoids.[7]

Conceptacles develop in a haphazard manner; cells in conceptacle regions deform one another and become less regularly shaped as they grow larger.[5]

In a similar fashion to the coralline algae, the outer layer of the thallus is shed seasonally, presumably to avoid colonization by epiphytes.[8]

Habitat

The freshwater species H. rivularis[6] and H. angularis[7] seems to form a clade,[9] and require an alkaline pH and hard water, preferring clean water.[10] Unlike most other freshwater red algae (which prefer running water), H. rivularis prefers still water, particularly shady lakes or ponds.[10] H. rubra and other marine species are found in brackish waters, but freshwater / gemma-bearing species cannot tolerate even moderate salinities.[11] The genus is often found in a symbiotic partnership with fungi.[12] Hildenbrandia has a remarkable tolerance to stresses including extreme temperatures, desiccation, and Ultra-violet light; it can be up and photosynthesizing near full capacity just minutes after being cooled to −17 °C or subjected to extreme salinities.[13]

Reproduction

Sexual reproduction has never been observed in any Hildenbrandia species.[11] It can reproduce by splitting into multiple colonies by fragmentation, or via stolons (i.e. sending out lateral branches) or gemmae.[6]

Marine Hildenbrandia, on the other hand, reproduce by means of tetraspores that are produced within the thallus by conceptacles.[7]

Systematics

The genus contains these species[14] (this list is out of date):

  • H. angolensis
  • H. arracana
  • H. canariensis
  • H. crouanii
  • H. crouaniorum
  • H. dawsonii
  • H. deusta
  • H. expansa
  • H. galapagensis
  • H. kerguelensis
  • H. lecannellieri
  • H. lithothamnioides
  • H. nardiana
  • H. occidentalis
  • H. pachythallos
  • H. patula
  • H. prototypus
  • H. ramanaginaii
  • H. rivularis
  • H. rosea
  • H. rubra
  • H. sanjuanensis
  • H. yessoensis

Stonehenge

The presence of H. rivularis near Stonehenge has been put forward as a reason for the site's perceived mystical properties. Flint in the Blick Mead spring pools near to the henge takes on a pink hue a couple of hours after being taken out of water due to the presence of the algae. It is assumed that ancient hunter-gatherers would have seen the rocks as having magical properties and would have deemed the site worthy of interest.[15] [16]

References
  1. Dethier, M. (1994). "The ecology of intertidal algal crusts: variation within a functional group". Journal of Experimental Marine Biology and Ecology. 177: 37–71. doi:10.1016/0022-0981(94)90143-0.
  2. Sherwood, A.; Sheath, R. (2000). "Biogeography and systematics of Hildenbrandia (Rhodophyta, Hildenbrandiales) in Europe: inferences from morphometrics and rbcL and 18S rRNA gene sequence analyses". European Journal of Phycology. 35 (2): 143–152. doi:10.1080/09670260010001735731.
  3. "Hildenbrandia Ben: Morphology". washington.edu.
  4. Cabioch, J.; Giraud, G. (1982). "La structure hildenbrandioïde, stratégie adaptative chez les Florideés". Phycologia (in French). 21 (3): 308–315. doi:10.2216/i0031-8884-21-3-307.1.
  5. Pueschel, C. (1982). "Ultrastructural observations of tetrasporangia and conceptacles in Hildenbrandia (Rhodophyta: Hildenbrandiales)". European Journal of Phycology. 17 (3): 333–341. doi:10.1080/00071618200650331.
  6. Wayne Nichols, H. (1965). "Culture and development of Hildenbrandia rivularis from Denmark and North America". American Journal of Botany. 52 (1): 9–15. doi:10.2307/2439969. JSTOR 2439969.
  7. Sherwood, A. R.; Sheath, R. G. (2000). "Microscopic analysis and seasonality of gemma production in the freshwater red alga Hildenbrandia angolensis (Hildenbrandiales, Rhodophyta)". Phycological Research. 48 (4): 241–249. doi:10.1046/j.1440-1835.2000.00208.x. S2CID 84193742.
  8. Pueschel, C. (1988). "Cell sloughing and chloroplast inclusions in Hildenbrandia rubra (Rhodophyta, Hildenbrandiales)". European Journal of Phycology. 23: 17–23. doi:10.1080/00071618800650021.
  9. Sherwood, A. R.; Sheath, R. G. (2003). "Systematics of the Hildenbrandiales (Rhodophyta): gene sequence and morphometric analyses of global collections". Journal of Phycology. 39 (2): 409–422. doi:10.1046/j.1529-8817.2003.01050.x. S2CID 86786840.
  10. Eloranta, P.; Kwandrans, J. (2004). "Indicator value of freshwater red algae in running waters for water quality assessment" (PDF). International Journal of Oceanography and Hydrobiology. XXXIII (1): 47–54. ISSN 1730-413X. Archived from the original (PDF) on 2011-07-27. Retrieved 2010-10-27.
  11. Sherwood, A. R.; Shea, T. B.; Sheath, R. G. (2002). "European freshwater Hildenbrandia (Hildenbrandiales, Rhodophyta) has not been derived from multiple invasions from marine habitats". Phycologia. 41: 87–95. doi:10.2216/i0031-8884-41-1-87.1. S2CID 84894072.
  12. Saunders, G. W.; Bailey, J. C. (1999). "Molecular systematic analyses indicate that the enigmatic Apophlaea is a member of the Hildenbrandiales (Rhodophyta, Florideophycidae)". Journal of Phycology. 35: 171–175. doi:10.1046/j.1529-8817.1999.3510171.x. S2CID 84758802.
  13. Garbary, D. (2007). "The Margin of the Sea". Algae and Cyanobacteria in Extreme Environments. Cellular Origin, Life in Extreme Habitats and Astrobiology. 11. pp. 173–191. doi:10.1007/978-1-4020-6112-7_9. ISBN 978-1-4020-6111-0.
  14. Guiry, M.D.; Guiry, G.M. (2008). "Hildenbrandia". AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Retrieved 2009-04-18.
  15. "Mesolithic settlement near Stonehenge: excavations at Blick Mead, Vespasian's Camp, Amesbury" (PDF). www.silversaffron.co.uk.
  16. Jacques, David (2014). "Mesolithic settlement near Stonehenge: excavations at Blick Mead, Vespasian's Camp, Amesbury". Wiltshire Archaeological and Natural History Magazine. 107: 7–27.
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