Belongs within: Corallinales.
The Lithophylloideae are coralline red algae in which cells of adjacent vegetative filaments are joined by secondary pit connections (Bailey 1999).
A coralline joint
Published 21 March 2023
Classification of the coralline red algae has historically swirled around a central conflict. On a superficial level, the corallines can be readily divided between ‘geniculate’ and ‘non-geniculate’ taxa. In geniculate species, the calcified thallus is divided into joints by non-calcified bands (the geniculae); such species usually have an upright growth habit. In non-geniculate species, the thallus forms a unified mass, and typically has a crustose habit. The question is whether this convenient division also reflects an underlying phylogenetic divide. And a good test case for this question can be found in the coralline subfamily Lithophylloideae.
When examined at the microscopic level, it can be seen that the thalli of corallines are made up of masses of filaments, a structure known as ‘pseudoparenchymatous’ (Bailey 1999). Where filaments come into contact, they may form connections in two ways: adjacent filaments may directly fuse with one another, or they may form secondary pit connections. Depending on the species, either one or the other connection may be present, or sometimes both. In Lithophyllum and related genera, thallus filaments form pit connections but do not fuse. However, such an arrangement is found in both geniculate and non-geniculate taxa. As a result, some authors have recognized a single subfamily Lithophylloideae for all taxa containing pit connections only, whereas others have divided them between non-geniculate LIthophylloideae and geniculate Amphiroideae.
Relationships between ‘lithophylloids’ and ‘amphiroids’ were tested using molecular data by Bailey (1999). The resulting tree identified both geniculate and non-geniculate taxa as non-monophyletic, with the geniculate Amphiroa more closely related to the non-geniculate Titanoderma than the geniculate Lithothrix. This could indicate that geniculae evolved on two separate occasions, or that they evolved once and were then lost in Titanoderma. However, it is notable that geniculae in the two genera are structurally distinct. In Lithothrix, palisades of long cells are calcified at one end of the cell but not at the other. In Amphiroa, geniculae represent tiers of entirely uncalcified cells.
Coralline algae in general have an extensive fossil record with Lithophylloideae dating back to at least the middle Miocene (Rösler et al. 2017). However, coralline fossils almost exclusively represent non-geniculate taxa; geniculate forms rapidly fall apart after dying and become unrecognisable. As such, the origins of geniculae seem doomed to remain a matter of inference.
Systematics of Lithophylloideae
Characters (from Bailey 1999): Bisporangia and/or tetrasporangia lacking apical plugs and produced in uniporate conceptacles. Cells of adjacent vegetative filaments joined by secondary pit connections, cell fusions rare. Genicula present or absent; when present, genicula composed of one or more tiers of uncalcified cells, nonmeristematic, often corticated.
<==Lithophylloideae [Amphiroideae, Dermatolitheae, Lithophylleae] |--+--Lithothrix Gray 1867HB03, B99 [Lithotricheae] | | `--L. aspergillum Gray 1867S57 | `--+--Titanoderma Nägeli 1858HB03, B99 [=Dermatolithon Foslie 1898B99] | | |--*T. pustulatumB99 (see below for synonymy) | | |--‘Dermatolithon’ dispar (Foslie) Foslie 1909 [=Fosliella dispar, Lithophyllum dispar]S57 | | `--‘Dermatolithon’ hapalidioidesPP64 | `--Amphiroa Lamouroux 1812HB03, HL09 [Amphiroeae] | |--A. ancepsG05 | |--A. beauvoisii Lamouroux 1816HS14 | |--A. elegans Harvey 1847L27 | |--A. foliacea Lamouroux 1824HS14 | |--A. fragilissima (Linnaeus) Lamouroux 1816 [=Corallina fragilissima Linnaeus 1758]HL09 | |--A. gracilis Harvey 1855HS14 | |--A. rigidaR26 | `--A. vanbosseaeN10 `--Lithophyllum Philippi 1837HB03, HL09 [incl. PseudolithophyllumHB03] |--*L. incrustans Philippi 1837 [incl. L. viennotii Lemoine 1929]BA05 |--L. byssoidesPP64 |--L. carpophylli (Heydr.) Fosl. 1909 [=Melobesia carpophylli Heydr. 1893, Dermatolithon carpophylli]L27 |--L. decipiens (Foslie) Foslie 1900S57 |--L. decussatum (Ell. & Solander) Fosl. 1909L27 |--L. dentatum (Kützing) Foslie 1898 [=Spongites dentata Kützing 1841]BA95 |--L. detrusum Fosl. 1906L27 |--L. exiguum Conti 1946BA95 |--‘Pseudolithophyllum’ expansumPP64 |--L. insipidum Adey, Townsend & Boykins 1982HS14 |--L. jugatum Fosl. 1906 [=Carpolithon jugatum]L27 |--L. kotschyanum Unger 1858HL09 |--L. lichenare Mason 1953S57 |--L. lichenoidesLLL03 |--L. neofarlowii Setchell & Mason 1943S57 |--L. nitorum Adey & Adey 1973 [incl. L. mgarrense Bosence 1983]BA95 |--L. orbiculatum (Foslie) Foslie 1900 [=Lithothamnion orbiculatum Foslie 1895]BA95 |--L. papillosumPP64 |--L. polymorphumB79 |--L. pygmaeum (Heydrich) Heydrich 1897HS14 |--L. racemusPP64 |--L. tamiense (Heydrich) Foslie 1900 [=Lithothamnion tamiense Heydrich 1897]HL09 |--L. tortuosum [=Tenarea tortuosa]PP64 |--L. trochanterPP64 |--L. tuberculatum Fosl. 1906L27 `--L. whidbeyense Foslie 1906S57 Lithophylloideae incertae sedis: Hydrolithon (Foslie) Foslie 1909HB03, HL09 [incl. GoniolithonHB03] |--H. farinosum (Lamouroux) Penrose & Chamberlain 1993 [=Melobesia farinosa Lamouroux 1916]HL09 |--H. gardineri (Foslie) Verheij & Prud’homme van Reine 1993 (see below for synonymy)HL09 |--‘Goniolithon’ improcerumHB03 |--H. munitum (Foslie & Howe) Penrose 1996HS14 |--H. onkodes (Heydrich) Penrose & Woelkerling 1992 (see below for synonymy)HL09 |--H. reinboldiiBB05 `--H. samoense (Foslie) Keats & Chamberlain 1994 [=Lithophyllum samoense Foslie 1906]HL09 PaulsilvellaHB03 Ezo Adey, Masaki & Akioka 1974B99 Tenarea Bory 1832B99 `--T. undulosaPP64
Hydrolithon gardineri (Foslie) Verheij & Prud’homme van Reine 1993 [=Lithophyllum gardineri Foslie 1907, Porolithon gardineri]HL09
Hydrolithon onkodes (Heydrich) Penrose & Woelkerling 1992 [=Lithothamnion onkodes Heydrich 1897, Porolithon onkodes]HL09
*Titanoderma pustulatumB99 [=Melobesia pustulata Lamouroux 1816BA95, Lithophyllum pustulatum (Lamouroux) Foslie 1904BA95]
*Type species of generic name indicated
References
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[BB05] Bassi, D., J. C. Braga, E. Zakrevskaya & E. P. Radionova. 2005. Re-assessment of the type collections of corallinalean genera (Corallinales, Rhodophyta) described by V. P. Maslov. Palaeontology 48 (5): 929–945.
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[N10] Norris, J. N. 2010. Marine algae of the northern Gulf of California: Chlorophyta and Phaeophyceae. Smithsonian Contributions to Botany 94: 1–276.
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[R26] Risso, A. 1826. Histoire naturelle des principales productions de l’Europe méridionale et particulièrement de celles des environs de Nice et des Alpes maritimes vol. 5. F.-G. Levrault: Paris.
Rösler, A., F. Perfectti, V. Peña, J. Aguirre & J. C. Braga. 2017. Timing of the evolutionary history of Corallinaceae (Corallinales, Rhodophyta). Journal of Phycology 53: 567–576.
[S57] Scagel, R. F. 1957. An annotated list of the marine algae of British Columbia and northern Washington (including keys to genera). National Museum of Canada Bulletin 150: 1–289.