Charles Darwin and the Phylogeny of State Flowers and State Trees

This is a guest post by Rachel Rodman. Photos by Daniel Murphy.


Every U.S. state has its own set of symbols: an official flower, an official tree, and an official bird. Collectively, these organisms form the stuff of trivia and are traditionally presented in the form of a list.

But, lists…well. As charming as lists can sometimes be, lists are rarely very satisfying.

So I decided to try something different.

I am not, of course, the first person to be unhappy with the eclectic, disordered nature of many biological assemblages. In the 18th century, Linnaeus developed a classification system in order to make sense of that untidiness. Kingdom, Phylum, Class, and so on.

In the 19th century, Darwin set biodiversity into an even more satisfying intellectual framework, outlining a model that linked organisms via descent from a series of common ancestors. And, as early as 1837, he experimented with a tree-like structure, in order to diagram these relationships.

Following Darwin’s lead, I’ve worked to reframe the state flowers and state trees in terms of their evolutionary history (*see the methods section below). And today, in honor of Darwin’s 209th birthday, I am delighted to present the results to you.

Let’s start with the state flowers.

In this tree, Maine’s “white pine cone and tassel” forms the outgroup. Among all the state “flowers,” it is the only gymnosperm—and therefore, in fact, not actually a flower.

Notice, also, that the number of branches in this tree is 39—not 50. Most of this stems from the untidy fact that there is no requirement for each state to select a unique flower. Nebraska and Kentucky, for example, share the goldenrod; North Carolina and Virginia share the dogwood.

With the branch labeled “Rose,” I’ve compressed the tree further. The state flowers of Georgia, Iowa, North Dakota, New York, and Oklahoma are all roses of various sorts; with my data set (*see methods below), however, I was unable to disentangle them. So I kept all five grouped.

This is a rich tree with many intriguing juxtapositions. Several clades, in particular, link geographical regions that are not normally regarded as having a connection. Texas’ bluebonnet, for example, forms a clade with Vermont’s red clover. So, similarly, do New Hampshire’s purple lilac and Wyoming’s Indian paintbrush.

Texas bluebonnet (Lupinus texensis) – the state flower of Texas

The second tree—the tree of state trees—is similarly rewarding. This tree is evenly divided between angiosperms (19 species) and gymnosperms (17 species).

Iowa’s state tree is simply the “oak”—no particular species was singled out. To indicate Iowa’s selection, I set “IA” next to the node representing the common ancestor of the three particular oak species: white oak, red oak, and live oak, which were selected as symbols by other states.

Arkansas’ and North Carolina’s state tree, similarly, is the “pine,”—no particular species specified. I’ve indicated their choice in just the same way, setting “AR” and “NC” next to the node representing the common ancestor of the eight particular pine species chosen to represent other states.

In this tree of trees, as with the tree of flowers, several clades link geographical regions that are not usually linked—at least not politically. Consider, for example, the pairing of New Hampshire’s white birch with Texas’ tree, the pecan.

Another phylogenetic pairing also intrigued me: Pennsylvania’s eastern hemlock and Washington’s western hemlock. It evokes, I think, a pleasing coast-to-coast symmetry: two states, linked via an east-west cross-country bridge, over a distance of 2,500 miles

The corky bark of bur oak (Quercus macrocarpa). Oak is the state tree of Iowa.

In this post, I’ve presented the U.S. state flowers and U.S. state trees in evolutionary framework. The point in doing that was not to denigrate any of the small, human stories that lie behind these symbols—all of the various economic, historical, and legislative vagaries, which led each state to select these particular plants to represent them. (Even more importantly, I have no wish to downplay the interesting nature of any of the environmental factors that led particular plants to flourish and predominate in some states and not others.)

The point, instead, was to suggest that these stories can coexist and be simultaneously appreciated alongside a much larger one: the many million year story of plant evolution.

With Darwin’s big idea—descent with modification—the eclectic gains depth and meaning. And trivia become a story—a grand story, which can be traced back, divergence point by divergence point: rosids from asterids (~120 mya); eudicots from monocots (~160 mya); angiosperms from gymnosperms (~300 mya), and so on and so on.

So today, on Darwin’s 209th, here, I hope, is one of the takeaways:

An evolutionary framework really does make everything—absolutely everything: U.S. state symbols included—more fun, more colorful, more momentous, and more intellectually satisfying.

Thanks, Darwin.


To build these two trees, I relied on a data set from, a website maintained by a team at Temple University. At the “Load a List of Species” option at the bottom of the page, I uploaded two lists of species in .txt format; each time, TimeTree generated a phylogenetic tree, which served as a preliminary outline.

Later, once I’d refined my outlines, I used the “Get Divergence Time For a Pair of Taxa” feature at the top of the page in order to search for divergence time estimates. As I reconstructed my trees in LibreOffice, I used these estimates to make my branch lengths proportional.


Rachel Rodman has a Ph.D. in Arabidopsis genetics and presently aspires to recontextualize all of history, literature, and popular culture in the form of a phylogenetic tree. Won’t you help her?


Children’s Books About Evolution

Evolution is a difficult subject to learn, let alone teach. Because evolution is generally such a slow process, it involves a timeline that is challenging for us to comprehend. Evolution is also commonly misunderstood, so misconceptions abound, be they purposeful misrepresentations, gaps in understanding, or otherwise. Wrapping one’s brain around even the basic tenets of evolution can take years of study, yet it is one of the most fundamental concepts of biology; failing to understand it stifles one’s knowledge of and appreciation for the study of life on Earth. On the flipside, gaining an understanding of the workings of evolution can inspire a greater appreciation for our place in the universe and can instill in oneself the urgency of conservation.

Despite being a tough subject to grasp, there is no reason why children should be exempt from learning about it. However, because it is such a complex topic, adults can struggle to find ways to explain it. Luckily, there are some great children’s books about evolution that introduce the subject in basic ways. These books are good starting points and can help cultivate a desire to explore the topic further. Understanding evolution and the science surrounding our world and the broader universe is a lifelong pursuit. Children will benefit from a head start.

What follows are reviews of a handful of books that may be useful in teaching kids about the theory of evolution.

I Used to Be a Fish by Tom Sullivan


This book is an excellent place to start. It is a quick and easy read, and it introduces – in a very simple way – the evolutionary lineage of humans. It doubles as a lesson on evolution and, as Sullivan puts it, “a tribute to every child’s power to transform their lives and to dream big,” which is achieved by highlighting the imagination of the main character and defining evolution as the gradual development over a lifetime towards achieving goals and aspirations.

In the Author’s Note, Sullivan briefly explains some important aspects of evolution: it is “a very slow process” that “occurs over generations to entire populations of creatures,” it doesn’t occur in a straight line like the book implies but instead looks “more like a tree with many complicated branches,” and “it doesn’t happen because a creature wants it to.”

One step in our evolutionary lineage as depicted in I Used to Be a Fish by Tom Sullivan

One step in our evolutionary lineage as depicted in I Used to Be a Fish by Tom Sullivan

Life history

Timeline from I Used to Be a Fish by Tom Sullivan. Look how far we’ve come!

Grandmother Fish by Jonathan Tweet; illustrated by Karen Lewis


This book is similar to Sullivan’s book, but it adds a little more detail to the story and invites interaction from its audience. As major periods in our evolutionary lineage are reached, readers are asked to “wiggle” like our Grandmother Fish, “crawl” like our Grandmother Reptile, “squeak” like our Grandmother Mammal, “hoot” like our Grandmother Ape, and so on. As the story transitions from one main character to another, simplified versions of evolutionary trees are shown (like the one below).


A larger version of “Our Evolutionary Family Tree” is featured at the end of the story followed by several pages of additional information that adults can use to further explain evolution to children, including discussions on three major concepts of evolution (descent with modification, artificial selection, and natural selection), more details on the main characters in the book, and a guide to correcting common errors about evolution.


When Fish Got Feet, Sharks Got Teeth, and Bugs Began to Swarm by Hannah Bonner


This book is much more text heavy than the first two, but is still very approachable. The illustrations are both humorous and informative, and Bonner excels at explaining complex topics in a way that makes them easy to digest. Rather than covering hundreds of millions of years of evolution like the first two books, this book focuses mainly on events that occurred during the Silurian and Devonian periods – between 360 and 444 million years ago. It was during this time that plants were making their way to land and diverging into many different forms. Arthropods were doing the same. During this period, the earth’s atmosphere became more oxygen rich and soil began to accumulate largely due to the growth and expansion of land plants.

Recipe for a land plant from When Fish Got Feet by Hannah Bonner

Recipe for a land plant from When Fish Got Feet by Hannah Bonner

This was also a period of great diversification in the fish world. Jaws were becoming more common and skeletons made of bone (as opposed to cartilage) were developing.  The first tetrapods (fish with legs) emerged from the oceans and onto land in the Devonian period. These tetrapods were our early ancestors, and Bonner explains how some of the skeletal features that fish developed during this time period were precursors to our current skeleton.

Unlike the first two books, the evolution of plants receives some attention in Bonner’s book. It is during the Devonian period that the first trees and seed-bearing plants appear. As in the other books, there are additional resources at the end, including this important warning by Bonner: “Please remember that anyone can set up a Web site, so not everything you will encounter will be good science.”

A time line of life on earth from When Fish Got Feet by Hannah Bonner

A timeline of life on earth from When Fish Got Feet by Hannah Bonner

Key to helping children understand evolution is understanding it ourselves, and there are, of course, endless resources out there to help with this. I will suggest just two additional books. In keeping with the spirit of children’s books, there is a great illustrated biography of Charles Darwin (who is considered the Father of Evolution) called Darwin For Beginners by Jonathan Miller and Borin Van Loon. It’s basically Darwin’s life told in graphic novel form. And keeping with the fish theme, you can’t go wrong with Neil Shubin’s, Your Inner Fish, a fascinating look into the origins of many of the parts, pieces, and other features of the human body.

Do you have a favorite book, children’s or otherwise, about evolution? Please share it in the comment section below.