DESCRIPTION OF THE GREEN ALGAE

EUKARYA> ARCHAEPLASTIDA> VIRIDIPLANTAE> GREEN ALGAE

INTRODUCTION TO THE GREEN ALGAE The Green Algae include a large, diverse assemblage of organisms. As presented here, they are all of the “green plants” that do not develop from embryos. As such they represent a grade of complexity rather than a taxonomic unit because they are not monophyletic. Indeed, they straddle both of the subkingdoms in the Viridiplantae. Their disparity in form, ultrastructure, and molecular structure is greater than that of all the other plants and warrants their separation into at least three phyla and perhaps as many as eleven phyla. The classification that follows is a modification of van den Hoek et al. (1995), and Graham and Wilcox (2000), who based their systems mainly on ultrastructural characters. The molecular relationships between groups of the green algae are illustrated well by Marin and Melkonian (1999), Turmel et al. (2008), and Proschold and Leliaert (2007). Figure 1 is a modification of Proschold and Leliaert (2007).

MAJOR CLADES OF THE GREEN ALGAE 1. CHLOROBIONTS, INCLUDING CLADES OF THE PRASINOPHYTES 2. CHLOROPHYTE CLADE 3. STREPTOBIONT CLADE 4. CHAROPHYTE CLADE 5. EMBRYOPHYTE CLADE

FIGURE 1. MAJOR CLADES OF THE GREEN ALGAE. Relationships between the Green Algae. This is an adaptation of Proschold and Leliaert (2007). 1. This includes all taxa that are Chlorobionts, 8 paraphyletic clades of Prasinophytes and the monophyletic Chlorophyta (clade 2). 2. The Chlorophytes make motile cells that have paired equal flagella, generally that are directed and inserted anteriorly. 3. This clade includes all plants that are Streptophytes: flagella inserted subapically, mitosis with cell plate formation, no centrioles, and no persistent nuclear envelope. 4. The Charophytes usually have simple life histories in which the zygote undergoes meiosis. The Embryophytes generally include those Streptophytes that have well-developed alternation of generation (gametophyte-sporophyte).

TABLE 1. GENERAL CHARACTERS OF THE GREEN ALGAL PHYLA. Information drawn from Marin and Melkonian (1999), Turmel et al. (2008), Proschold and Leliaert (2007), Bold et al. (1987), Hoek et al. (1995), and Graham and Wilcox (2000).
Characters	Prasinophyta	Chlorophyta	Charophyta
mitosis	closed; centric	closed; centric	open; acentric
cytokinesis	furrowing; phycoplast	furrowing; phycoplast	cell plate; phragmoplast
cell wall	cellulosic scales	continuous cellulosic wall; some complex with mucilage	continuous cellulosic wall; some complex with mucilage
flagella	anteriorly-directed (usually); covered with scales; usually subapical; a few with basal bodies associated with a multilayered structure	anteriorly-directed; usually naked; apically inserted	anteriorly-directed; covered with scales; usually subapical; basal bodies associated with a multilayered structure
life history	one known; haplontic	usually haplontic; some diplontic or haplodiplobioltic (alternation of hapliod and diploid vegetative phases)	usually haplontic

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By Jack R. Holt. Last revised: 03/24/2013