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Green algae

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Are green algae plants?

Red algae and brown algae aren’t plants – they’re protists – an entirely different kingdom of life.

Blue-green algae – photosynthetic bacteria.

But what about green algae – are they plants?

It depends on whom you ask:

Green Algae_Pond

Image from Slideshare.net/VijayaraghavanGonuguntla/effluent-treat

Types of algae

The Green Algae Tree of Life (GrAToL)

Botanists (plant scientists) consider green algae plants:

They perform photosynthesis using chlorophyll.
They are the ancestors of modern day land-plants.
They’re part of the land-plant family tree.
End of story -> Plants! 🙂

Zoologists (animal and protist scientists) classify green algae as protozoans (not plants)

In this view, green algae can’t be plants because:

1) Most are single-celled (unicellular), too small to be seen without a microscope.
2) When not single celled, they live in colonies. Don’t form plant tissue.
3) They can move on their own. Some swim with flagella.
4)  They have no vascular system to transport nutrients.
5) They do not have true roots, shoots, or veins.
6)  They have no stems, leaves or roots.

Why can’t the answer be a simple “yes they are” or “no they are not?” Because life wasn’t created with well-defined boundaries – and life today still doesn’t have such boundaries. Life started as simple organisms, and developed over time, slowly branching out to create new forms, with new characteristics. Today’s green algae resembles the early forms of life that later gave rise to both plants and to protists.  It is a kind of “living fossil.

Plant and green algae family tree

Plant Green Algae Prasinophytes chlorophytes clade

from Leliaert F., Verbruggen H. & Zechman F.W. (2011) Into the deep: New discoveries at the base of the green plant phylogeny. BioEssays 33: 683-692

Frederik Leliaert writes:

This figure shows the phylogenetic relationships among the main lineages of green plants. The tree topology is a composite on accepted relationships based on molecular phylogenetic evidence. Uncertain phylogenetic relationships are indicated by polytomies. The divergence times are rough approximations based on the fossil record and molecular clock estimates. These age estimates should be interpreted with care as different molecular clock studies have shown variation in divergence times between major green plant lineages.  Drawings illustrate representatives of each lineage.

Source: Leliaert F., Verbruggen H. & Zechman F.W. (2011) Into the deep: New discoveries at the base of the green plant phylogeny. BioEssays 33: 683-692


Learning Standards

Massachusetts Science and Technology/Engineering Curriculum Framework

Life Science (Biology), Grades 6–8. Classify organisms into the currently recognized kingdoms according to characteristics that they share. Be familiar with organisms from each kingdom.

Biology, High School – 5.2 Describe species as reproductively distinct groups of organisms. Recognize that species are further classified into a hierarchical taxonomic system (kingdom, phylum, class, order, family, genus, species) based on morphological, behavioral, and molecular similarities.

Benchmarks for Science Literacy, American Association for the Advancement of Science

Students should begin to extend their attention from external anatomy to internal structures and functions. Patterns of development may be brought in to further illustrate similarities and differences among organisms. Also, they should move from their invented classification systems to those used in modern biology… A classification system is a framework created by scientists for describing the vast diversity of organisms, indicating the degree of relatedness between organisms, and framing research questions.

SAT Biology Subject Area Test

Evolution and diversity: Origin of life, evidence of evolution, patterns of evolution, natural selection, speciation, classification and diversity of organisms.

Teaching About Evolution and the Nature of Science, National Academy Press (1998)

Biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships. Species is the most fundamental unit of classification.


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