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1 GELIDIALES Wilson Freshwater University of North Carolina at Wilmington.

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1 1 GELIDIALES Wilson Freshwater University of North Carolina at Wilmington

2 2 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: Freshwater DW et al. (1995) J. Phycol. 31: Hommersand MH & Fredericq S (1988) Phycologia 27: Lamouroux JVF (1813) Ann. Mus. Natl. Hist. Nat. 20: Papenfuss GF (1966) Phycologia 5: Rodriguez D & Santelices B (1988) Taxonomy of Economic Seaweeds...Vol. II. Pp Santelices B (1990) Hydrobiologia 204/205: Shimada S et al. (1999) Phycologia 38: Tronchin EM et al. (2002) Bot. Mar. 45: Tronchin EM & Freshwater DW (2007) Phycologia 46: GELIDIALES

3 3 -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 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? What to look for when identifying Gelidiales species

4 4 Apical Cell single apical cell multiple apical cells Gelidiales will have a single apical cell Gelidiopsis, Wurdmania will have multiple apical cells Millar & Freshwater 2005 Littler & Littler 2000

5 5 Transverse Section Characters Are there rhizines? no rhizines NO Gelidiella Parviphycus rhizines scattered in medulla rhizines concentrated in central medulla rhizine pattern may not be consistent YES Gelidium Pterocladiella Millar & Freshwater 2005 Rico et al Thomas & Freshwater 2001

6 6 Transverse Section Characters What is shape? Is medullary cell arrangement distinct near apical tips? terete sub-terete compressed flattened central axial cell 3 rd order branch cell 2nd order branch cells central axial cells 2nd order branch cells NO Gelidiella YES Parviphycus Millar & Freshwater 2005

7 7 Cystocarps characters Gelidium Bilocular cystocarp Central bisecting placental tissue Two ostioles Carpogonia develop on both sides of blade Nutritive filaments develop around 2 nd 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 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 Millar & Freshwater 2005 Thomas & Freshwater 2001 Tronchin & Freshwater 2007

8 8 Rhizoids-holdfasts Refined and expanded by Perrone et al. (2006) Botanica Marina 49:23-33.

9 9 Rhizoids-holdfasts Gelidiella & Parviphycus (Gelidiellaceae) Independent unicellular rhizoidal filaments originating from surface cortical and that remain in open connection with their mother cells 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 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 “independent” “peg” “tapered” Millar & Freshwater 2005 Tronchin in Millar & Freshwater 2005 Millar & Freshwater 2005 Rico et al Tronchin & Freshwater 2007

10 10 Tetrasporangial branch characters sterile margin no sterile margin Is there a sterile margin? chevrons Less organized How are tetrasporangia arranged? specific or non-specific number per segment Millar & Freshwater 2005 Thomas & Freshwater 2001 Millar & Freshwater 2005 Santelices 2002 Abbott 1999

11 11 Some Caribbean Species of the Bocas Region Gelidium microdonticum Small turfy species with flattened blades that have serrated margins. Pterocladiella bartlettii 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. Pterocladiella caerulescens (including P. beachiae) Small flattened species constricted branch bases, monoecious Thomas & Freshwater 2001 Millar & Freshwater 2005

12 12 This presentation is a contribution of the Pan-American Advanced Studies Institute


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