Are Algae Plants?


I was nibbling on some nori the other day when a thought suddenly hit me. I don't know squat about algae. I know it comes in many shapes, sizes, and colors. I know it is that stuff that we used to throw at each other on the beach. I know that it photosynthesizes. That's about it. What are algae? Are they even plants?

The shortest answer I can give you is "it depends." The term algae is a bit nebulous in and of itself. In Latin, the word "alga" simply means "seaweed." Algae are paraphyletic, meaning they do not share a recent common ancestor with one another. In fact, without specification, algae may refer to entirely different kingdoms of life including Plantae (which is often divided in the broad sense, Archaeplastida and the narrow sense, Viridiplantae), Chromista, Protista, or Bacteria.

Caulerpa racemosa , a beautiful green algae.

Caulerpa racemosa, a beautiful green algae.

Taxonomy being what it is, these groupings may differ depending on who you ask. The point I am trying to make here is that algae are quite diverse from an evolutionary standpoint. Even calling them seaweed is a bit misleading as many different species of algae can be found in fresh water as well as growing on land.

Cyanobacteria are photosynthetic bacteria, not plants.

Cyanobacteria are photosynthetic bacteria, not plants.

Take for instance what is referred to as cyanobacteria. Known commonly as blue-green algae, colonies of these photosynthetic bacteria represent some of the earliest evidence of life in the fossil record. Remains of colonial blue-green algae have been found in rocks dating back more than 4 billion years. As a whole, these types of fossils represent nearly 7/8th of the history of life on this planet! However, they are considered bacteria, not plants.

Diatoms (Chromista)

Diatoms (Chromista)

Diatoms (Chromista) are another enormously important group. The single celled, photosynthetic organisms are encased in beautiful glass shells that make up entire layers of geologic strata. They comprise a majority of the phytoplankton in the world's oceans and are important indicators of climate. However, they belong to their own kingdom of life - Chromista or the brown algae.

To bring it back to what constitutes true plants, there is one group of algae that really started it all. It is widely believed that land plants share a close evolutionary history with a branch of green algae known as the stoneworts (order Charales). These aquatic, multicellular algae superficially resemble plants with their stalked appearance and radial leaflets.

A nice example of a stonewort ( Chara braunii ).

A nice example of a stonewort (Chara braunii).

It is likely that land plants evolved from a Chara-like ancestor that may have resembling modern day hornworts that lived in shallow freshwater inlets. Estimates of when this happen go back as far as 500 million years before present. Unfortunately, fossil evidence is sparse for this sort of thing and mostly comes in the form of fossilized spores and molecular clock calculations.

Porphyra umbilicalis   - One of the many species of red algae frequently referred to as nori.

Porphyra umbilicalis  - One of the many species of red algae frequently referred to as nori.

Now, to bring it back to what started me down this road in the first place. Nori is made from algae in the genus Porphyra, which is a type of Rhodophyta or red algae. Together with Chlorophyta (the green algae), they make up some of the most familiar groups of algae. They have also been the source of a lot of taxonomic debate. Recent phylogenetic analyses place the red algae as a sister group to all other plants starting with green algae. However, some authors prefer to take a broader look at the tree and thus lump red algae in a member of the plant kingdom. So, depending on the particular paper I am reading, the nori I am currently digesting may or may not be considered a plant in the strictest sense of the word. That being said, the lines are a bit blurry and frankly I don't really care as long as it tastes good.

Photo Credits: [1] [2] [3] [4] [5] [6]

Further Reading: [1] [2] [3] [4]




There are many luxuries that we take for granted that are rather recent developments in our history. One such luxury is avoiding what was known as milk sickness. During the 19th century, milk sickness claimed the lives of countless thousands and it did so in a very violent manner, often manifesting in serious tremors, vomiting, coma and eventually death. It took a long time for early settlers to figure out what was causing milk sickness. We owe it to a woman named Dr. Anna Pierce Hobbs Bixby along with the rumored input of a Shawnee woman for getting to the root of the mystery.

As it turns out, milk sickness is caused from consuming the meat or milk of cattle that have fed on white snakeroot (Ageratina altissima). Once belonging to the same genus as boneset and Joe Pye weed, white snakeroot loves growing in the same kinds of areas that settlers grazed their cattle. It contains a toxin known as tremetol that, when consumed by cattle, builds up in the meat and milk. If cattle products are then ingested by humans, milk sickness is soon to follow. Famously, Abraham Lincoln's mother is said to have been killed by milk sickness.

White snakeroot blooms in late summer and continues through fall. In some areas it is the dominant species growing, which is great if you are one of the many pollinators that utilize this plant. Thankfully, today milk sickness is an almost unheard of occurrence and we owe much of that to Dr. Bixby.

Further Reading:

The Truth About Clover


Irish or not, four-leaf clovers are ingrained in our culture. They are a symbol of good luck and finding one is quite exciting. When one speaks traditionally about finding a four-leaf clover they are usually referring to a member of the genus Trifolium, which is a genus of true clovers in the legume family. As the generic name suggests, true clovers typically exhibit leaves of three. 

The odds of finding a four-leaf clover is roughly 1 in 10,000. You stand the best chance of finding them in patches of either white clover (Trifolium repens) or red clover (Trifolium pratense), which are actually native to parts of Europe and Africa. The mutation doesn't stop at four leaves either. Clovers with five or more leaves have been found and the world record for most leaves on a single clover is 56! What causes this mutation is a bit of a mystery. Some feel that it is environmental while others feel it is the result of recessive genes. A study done on white clover lends some support to the genetic connection. 

I find it interesting that some of the most the famous depictions of four-leaf "clovers" are not clovers at all but rather varieties of Oxalis tetraphylla. This Mexican species produces leaves divided into four with the characteristic lobe-like shape. Since it only ever produces four leaves, it is a failsafe for those looking to add a bit of "luck" to the season. 

Photo Credit: loriejeanne (

Further Reading: