GELIDIALES
Wilson Freshwater
University of North Carolina at Wilmington
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GELIDIALES
The Gelidiales are a relatively small red algal order that includes species of economic importance as sources of high quality agars.
Lamouroux chose the name Gelidium when originally describing the type genus because “most of the species composing it can be
reduced to a gelatinous substance by boiling and maceration” (Lamouroux 1813:40). Kylin (1923) erected the order Gelidiales based on
the presence of a diplobiontic life cycle and absence of typical auxiliary cells. Papenfuss (1966) further characterized the order by the
presence of nutritive cells formed during carpogonial development, apical growth by transverse division of a single apical cell, and
“Gelidium-type” spore germination (Chihara & Kamura 1963). Hommersand & Fredericq (1988) conducted detailed morphological studies
of vegetative and reproductive development and redefined the order.
Despite the economic importance of some Gelidiales species, solid vegetative characters for recognizing genera and species are
generally lacking (e.g. Rodriguez & Santelices 1988, Satelices 1990), and reproductive structures are often not available on specimens
collected in nature. Consequently the classification of genera and species in the order has been difficult, and its taxonomy historically
confused. Molecular analyses have proven very useful for resolving the relationships of Gelidiales species (e.g. Freshwater et al. 1995,
Shimada et al. 1999) and integrated molecular and morphological analyses are refining the intra-ordinal classification of the Gelidiales
(e.g. Tronchin et al. 2002, Tronchin & Freshwater 2007).
Wynne (1998) lists 23 Gelidiales species in the Caribbean. Six of these reports are questionable and probably do not represent
Caribbean species. Many are inconspicuous and part of the algal turf community. These turf species may be exceptionally difficult to
identify.
Chihara M & Kamura S (1963) Phycologia 3:69-74.
Freshwater DW et al. (1995) J. Phycol. 31:616-632.
Hommersand MH & Fredericq S (1988) Phycologia 27:254-272.
Lamouroux JVF (1813) Ann. Mus. Natl. Hist. Nat. 20:21-47.
Papenfuss GF (1966) Phycologia 5:247-255.
Rodriguez D & Santelices B (1988) Taxonomy of Economic Seaweeds...Vol. II. Pp. 115-125.
Santelices B (1990) Hydrobiologia 204/205:125-135.
Shimada S et al. (1999) Phycologia 38:528-540.
Tronchin EM et al. (2002) Bot. Mar. 45:548-558.
Tronchin EM & Freshwater DW (2007) Phycologia 46:325-348.
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What to look for when identifying Gelidiales species
-Is there a single apical cell?
(will separate small gelids from other wirey turfs like Gelidiopsis and Wurdmania)
-Size of thallus?
-What does it look like in transverse section?
Are there rhizines? (cells with thick walls & tiny lumens)
What is x.s. shape? (terete, compressed, flattened)
Is the arrangement of medullary cells distinct near apical tips?
-What do cystocarps look like?
Bilocular or unilocular?
How are nutritive filaments, gonimoblast, carpospores arranged?
-What do tetrasporangial branches look like?
Is there a sterile margin?
How are tetrasporangia arranged (number per segment, pattern)?
-How are rhizoidal holdfast arranged? (Perrone et al. 2006. Botanica Marina 49:23-33)
Are they scattered, clumped as brushes or cylindrical or tapered pegs?
-What does branching look like?
Are branch bases constricted, tapered, or not?
Are reproductive branchlets clustered in lower parts of thallus?
Is there a bilateral series of small branchlets along the main axis?
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Apical Cell
single apical cell
Millar & Freshwater 2005
Gelidiales will have a
single apical cell
Millar & Freshwater 2005
Millar & Freshwater 2005
multiple apical cells
Gelidiopsis, Wurdmania
will have multiple apical
cells
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Littler & Littler 2000
Littler & Littler 2000
Transverse
Section
Characters
Are there rhizines?
Rico et al. 2002
NO
Gelidiella
Parviphycus
no rhizines
Millar & Freshwater 2005
rhizine pattern may not be consistent
Thomas & Freshwater 2001
rhizines scattered in
medulla
Thomas & Freshwater 2001
rhizines concentrated
in central medulla
YES
Gelidium
Pterocladiella
Thomas & Freshwater 2001
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Transverse
Section
Characters
What is shape?
Millar & Freshwater 2005
compressed
terete
Millar & Freshwater 2005
sub-terete
flattened
Millar & Freshwater 2005
Millar & Freshwater 2005
Is medullary cell arrangement distinct near apical tips?
central axial cell
3rd order branch cell
NO
Gelidiella
2nd order branch cells
YES
Parviphycus
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Millar & Freshwater 2005
Millar & Freshwater 2005
central axial cells
2nd order branch cells
Cystocarps
characters
Millar & Freshwater 2005
Millar & Freshwater 2005
Millar & Freshwater 2005
Gelidium
Millar & Freshwater 2005
Bilocular cystocarp
Central bisecting placental tissue
Two ostioles
Carpogonia develop on both sides of blade
Nutritive filaments develop around 2nd order branch cells
Pterocladiella
Unilocular cystocarp
Placental tissue surrounds central axis
One ostiole (usually)
Carpogonia develop only as part of cell filaments
immediately adjacent to the central axis
Nutritive filaments develop around central axis
Thomas & Freshwater 2001
Tronchin & Freshwater 2007
Tronchin & Freshwater 2007
Pterocladia
Unilocular cystocarp
Placental tissue on floor of cystocarp cavity
One ostiole
Carpogonia develop on one sides of blade
If you see anything like this you’ll be famous
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Millar & Freshwater 2005
Rhizoids-holdfasts
Refined and expanded by Perrone et al. (2006) Botanica Marina 49:23-33.
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Rhizoids-holdfasts
Gelidiella & Parviphycus (Gelidiellaceae)
Independent unicellular rhizoidal filaments originating
from surface cortical and that remain in open connection
with their mother cells
Rico et al. 2002
“independent”
Millar & Freshwater 2005
Gelidium & Ptilophora? (Gelidiaceae)
Complex brush-like haptera consisting of both internal
rhizoidal filaments growing independently and between
surface cortical cells, and pigmented multicellular
uniseriate filaments originating from surface cortical cells.
Rhizoidal filaments independently attaching to or
penetrating the substrate
“peg”
Tronchin in Millar & Freshwater 2005
Millar & Freshwater 2005
Pterocladia & Pterocladiella (Pterocladiaceae)
Complex peg-like haptera consisting of both internal
rhizoidal filaments coalescing in a thick sheath and
protruding between surface cortical cells, and pigmented
multicellular uniseriate filaments originating from surface
cortical cells around the hapteron base and forming a
basal cortication. Coalesced rhizoidal filaments attaching
to or penetrating the substrate
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“tapered”
Tronchin & Freshwater 2007
Tronchin & Freshwater 2007
Tetrasporangial
branch
characters
Is there a sterile margin?
Millar & Freshwater 2005
sterile margin
Thomas & Freshwater 2001
How are tetrasporangia arranged?
Millar & Freshwater 2005
Millar & Freshwater 2005
no sterile margin
Millar & Freshwater 2005
chevrons
Millar & Freshwater 2005
specific or
non-specific
number per
segment
Millar & Freshwater 2005
Less organized
Millar & Freshwater 2005
Santelices 2002
Abbott 1999
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Some Caribbean Species
of the Bocas Region
Gelidium microdonticum
Small turfy species with flattened
blades that have serrated margins.
Thomas & Freshwater 2001
Pterocladiella bartlettii
Thomas & Freshwater 2001
Small slender species often with a
bi-lateral series of small branchlets
along the main branch.
Gelidium floridanum
Small to medium species with
reproductive branches often
clustered towards the base of
thallus; apex of main axes
sometimes elongated, and
tetrasporangial branchlets with a
wide sterile margin.
Thomas & Freshwater 2001
Pterocladiella caerulescens
(including P. beachiae)
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Small flattened species constricted
branch bases, monoecious
Millar & Freshwater 2005
Thomas & Freshwater 2001
This presentation is a contribution of the
Pan-American Advanced Studies Institute
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