DESCRIPTION OF THE PHYLUM GLAUCOPHYTA (SKUJA 1948)

EUKARYA> ARCHAEPLASTIDA> RHODOPLANTAE> GLAUCOPHYTA

Glaucophyta (glau-KA-fa-ta) is formed from two Greek roots that mean blue-green (glauko -γλαυκο); and plant (phyto -φυτό). The reference is to the blue-green color of the cyanelles. Glaukos also was a Greek sea god.

INTRODUCTION TO THE GLAUCOPHYTA All glaucophytes occur in freshwater, but are rarely observed. They tend to be coccoid and occur in loose colonies formed by the persistent cell wall of the parent cell following division (Figure 1). When they form motile cells (Figure 2), the flagella are heterodynamic and covered with mastigonemes. The base of the flagellar apparatus is associated with a multilayered structure (MLS) and cruciate flagellar roots, characters also associated with the Praesinophyta (in the Viridiplantae). They are clearly blue-green and their plastids retain aspects of the primary cyanobacterial endosymbiont not seen in any other taxa (except an unrelated euglyphid amoeba or Cyanomonas). Because the endosymbionts retain a thin murein wall and appear to be cyanobacterial, the plastids are usually called cyanelles (Figure 3). They have subsurface sacs, a character that Patterson (1999) listed as an identifying synapomorphy. If these sacs are alveoli, they might destroy the defining synapomorphy of the Alveolatae.

FIGURE 1. Glaucocystis, a coccoid taxon. Image from http://silicasecchidisk.conncoll.edu/LucidKeys/Carolina_Key/html/Glaucocystis_Main.html	FIGURE 2. A motile cell of Cyanophora. Note the heterodynamic flagella (text with tooltip) Heterodynamic flagella occur on the same cell but beat with different patterns (e.g. anterior-posterior). . Image from http://microscope.mbl.edu/baypaul/microscope/images/t_imgAZ/cyanophora_bgw.jpg	FIGURE 3. A TEM micrograph of Glaucosphaera that shows the cyanobacterial nature of the cyanelles. Image from http://www.biologie.uni-hamburg.de/b-online/d42/10.htm

SYSTEMATICS OF THE GLAUCOPHYTA Moreira et al. (2000) and supertree analyses (Baldauf 2003, Keeling 2004, and Nikolaev et al. 2004) confirm the monophyly of the three groups: the red algae, the green plants, and the glaucophytes. Cavalier-Smith (2002 and 2003) interprets the Rhodophytes and Viridiplantae as sister groups while the Glaucophytes are outgroups within the plant clade. This topology has been recovered Reyes-Prieto and Bhattacharya (2007) and Burki et al. (2008). Other analyses (Bhattacharya et al. 1995, Nikolaev et al. 2004, Kim and Graham 2008) showed them to be very different from the viridiplantae+rhodophytae. The elucidation of the relationships between this phylum and other members of the eukaryotes beyond the primary primary photosymbionts may serve to determine the topology of the Bikont tree. In the past they have been classified with the cryptophytes (Bourrelly 1970, Moestrup 1982), the chlorophytes (Bourrelly 1966), rhodophytes (Schnepf and Brown 1971, Cavalier-Smith 1982 and 1986, Melkonian 1984), and the chlorophytes+euglenophytes (Moestrup 1982, Melkonian 1982 and 1983, Kies and Kremer 1990). Patterson (1999) includes the glaucophytes in his list of sisterless taxa, but includes Cyanidium in that group. Since 1990, the group has been classified independently as its own phylum (e.g. Kies and Kremer 1990, Patterson 1999, Graham and Wilcox 2000, Van den Hoek et al. 1995, and Lee 1999). We have given them a tentative position as a basal group within the red algae after Cavalier-Smith (1981 and 1988) and Doweld (2001).

FIGURE 4. Relationship between the Glaucophyta and other phyla of the Archaeplastida after Cavalier-Smith (1981 and 1988) and Doweld (2001).

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By Jack R. Holt. Last revised: 03/19/2013