RICOCHETSCIENCE.COM: Unveiling the Origins of the Plants

Unveiling the Origins of the Plants

While it is clear that plants evolved from a green algal ancestor some 470-500 MYA, the question has always been.. which one? We know that plants and the green algae share the same photosynthetic pigments (chlorophyll a and b), store their energy as starch, and contain the fiber cellulose in their cell walls. But that is a general description for many of the green algae. After all, there are lots of green algae, from the mobile Chlamydomonas to the multicellular Ulva. Saying that the ancestor of the plants was a green algae is like saying that your ancestors came from Europe, a nice general statement, but it really doesn't tell you much about who you are.

Biology, 10th edition - McGraw-Hill Publishing, used by permission

A team of researchers out of Germany and Canada have provided a possible answer to this question - a group of conjugating algae that includes Spirogyra. Conjugating green algae reproduce sexually by temporarily linking the cytoplasm of two cells, allowing the exchange of genetic information. By studying the genomics of over forty different types of green algae, the researchers were able to construct an evolutionary tree that suggests that Spirogyra, or its close relatives, were the ancestor of the green plants. (these trees are available online)

Spirogyra is no stranger to the introductory biology classroom. Since it is easy to culture and observe, it is a common specimen in freshman labs. Furthermore, as can be seen in the video below, it has a unique configuration of its cloroplasts that gives the organism its name.

So the next time Spirogyra is mentioned, don't consider it just another green algae. Instead, think of it as one of those pivotal species that played an important role in forming the ecosystems that are the basis of our modern world.