Question

Evolution has been a common theme throughout this course. Beginning with a heterotrophic protist from the super group Archaeplastida, describe the major evolutionary steps that have resulted in the Kingdom Viridiplantae. For full points, be sure to correctly use the following terms in your answer: common ancestor, green algae, secondary endosymbiosis, chlorophyl a & b, embryophytes, monophyletic

Answer 1

Viridiplantae (literally "green plants")nare a clade of eukaryotic organisms that comprise approximately 450,000–500,000 species and play an important roles in both terrestrial and aquatic ecosystems. The green lineage (Viridiplantae) comprises the green algae and their descendants the land plants, and is one of the major groups of oxygenic photosynthetic eukaryotes.

The green lineage originated following an endosymbiotic event in which a heterotrophic eukaryotic host cell captured a cyanobacterium that became stably integrated and ultimately turned into a plastid.  This primary endosymbiosis, which likely happened between 1 and 1.5 billion years ago, marked the origin of the earliest oxygenic photosynthetic eukaryotes. The Viridiplantae are comprised of two clades—the Chlorophyta and the Streptophyta.

From this starting point, photosynthesis spread widely among diverse eukaryotic protists via secondary and tertiary endosymbioses, which involved captures of either green or red algae by non-photosynthetic protists

Secondary endosymbioses involving green algae as the autotrophic partner have given rise to three groups of algae: the chlorarachniophytes, the photosynthetic euglenids and the “green” dinoflagellates

The other eukaryotic algal groups, the cryptophytes, haptophytes, photosynthetic stramenopiles (e.g., diatoms, chrysophytes and brown seaweeds) and dinoflagellates, have acquired plastids from a red algal ancestor, either by a single or multiple endosymbiotic events

Chlorophyta Streptophyta Land plants charophytes core chlorophytes Ulvophyceae Chlorophycese Trebouviophyceae prasinophytes Chlorodendrophyceae Picocystis Mariellophyceae Pyramimonadales Coleochatophyceae Zygnematophyceae Charophyceae Pycnococcaceae Klebsordiophyceae Nephrosemido phyceae Chlorokybophyceae Prasinococcales AGE Palmophyllales Mestigatophyceae Puteti secondary symbious in progress Matene Katablepharid Secondary endosymbios Euglenophytes Chlorarachnio- phytes Serial secondary endosymbiosis Green dinoflagellates Putative ancient endosymbioses Chromalcolates Choanoflagellates Leiartolot Rex. Plot S3166 (2012

Members of the Chlorophyta are common inhabitants of marine, freshwater and terrestrial environments and exhibit a remarkable morphological diversity . As one of the deepest branches of the green lineage, the Streptophyta are certainly old, quite likely a billion years or more, and both molecular sequence divergence and the few available fossils are consistent with that view.