The Gelidiales is a relatively small order of red algae containing ca. 130-140 species placed in ten recognized genera. Many gelidialean species are economically important as sources of high quality agars. The order is defined by the unique set of characters listed below.
Species within the Gelidiales share a unique set of characters that make this a well-defined order of red algae. These characters include:
- a triphasic life history with isomorphic gameto- and tetrasporophytes
- agar as a cell wall component
- pit plugs with a single cap layer
- a special "Gelidium-type" spore germination pattern
- uniaxial filaments that branch in three planes forming a pseudoparenchyma
- intercalary carpogonia that after fertilization produce gonimoblasts that connect to nutritive cells
- transversely divided spermatangia
Evolution and Systematics
Discussion of Phylogenetic Relationships
Tree based on Freshwater et al. 1995, Freshwater and Bailey 1998, Shimada et al. 1999, Rico et al. 2002, and Freshwater unpublished. Clade labels refer to the type of morphology and development of the female reproductive system and carposporophyte as discussed in Bailey and Freshwater (1997).
Four major lineages have been identified by molecular analyses of taxa within the Gelidiales (Bailey and Freshwater 1997, Freshwater et al. 1995, Freshwater and Bailey 1998, Shimada et al. 1999). The morphology and development of the female reproductive system and carposporophyte may also define these lineages (Bailey and Freshwater 1997, Hommersand and Fredericq 1988, 1996, Santelices and Hommersand 1997). Three of the lineages are equivalent to the monophyletic genera Pterocladiella, Pterocladia, and Gelidiella. The fourth lineage defines a large clade that includes species of Acanthopeltis, Capreolia, Gelidium, Porphyroglossum, and Ptilophora. As noted on the Gelidiales tree above, species representing four other genera are also resolved within this lineage, but recent studies have synonimized these with currently recognized genera (Norris 1987, Shimada et al. 1999, Tronchin et al. 2003a). Analyses of nuclear-encoded 28S rRNA gene sequence data (Freshwater and Bailey 1998) and a combined four gene data set (Freshwater unpublished) have resolved Pterocladia and Pterocladiella as sister taxa, but relationships among the four major lineages can not currently be determined based upon non-molecular characters. The morphology and development of the Gelidiella female reproductive system and carposporophyte is unknown, and therefore the associated characters, which define the other three lineages, cannot be used to determine phylogenetic relationships among them.
Most species included in molecular analyses have been resolved within the "Gelidium" lineage. As noted above, this lineage includes species of not only Gelidium, but four other currently recognized genera as well. Molecular analyses identify at least eight clades within this lineage that have been referred to as "species complexes" or "species clades" (Freshwater and Rueness 1994, Freshwater et al. 1995, Shimada et al. 1999, Tronchin et al. 2003a). In contrast to the four major gelidialean lineages, morphological and/or developmental synapomorphies are unverified for all but the Ptilophora clade. The vegetative thalli of all species in the Ptilophora clade are constructed of four tissue layers composed of different cell types (Tronchin et al. 2003b). Santelices (1999) has defined a number of characters associated with the development of the cystocarp that may be synapomorphies for species clades within the "Gelidium" lineage. Further study is needed to determine if these or other characters will be useful for phylogenetic analyses.
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimens with Sequences:950
Specimens with Barcodes:422
Species With Barcodes:129
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