Phylogenetic Arts and Crafts

This is a guest post by Rachel Rodman.

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The foods we eat – namely fruits, vegetables, and grains – are all products of their own evolutionary stories. Some of the most well-known chapters in these stories are the most recent ones – dramatic changes in size and shape mediated by human selection.

One especially striking example is that of Brassica oleracea –the source of broccoli, cauliflower, kale, Brussels sprouts, kohlrabi, and cabbage. Each of these diverse vegetables belongs to the same species, and each is the product of a different kind of selection, exerted on different descendants of a common ancestor.

Corn is another famous chapter. The derivation of corn – with its thick cobs and juicy kernels developed from the ancestral grain teosinte, which it barely resembles – has been described as “arguably man’s first, and perhaps his greatest, feat of genetic engineering.”

But these, again, are recent chapters. Relatively. They unfolded over the course of consecutive human lifetimes –hundreds of years or thousands at the outset (sometimes much less). They are the final flourishes (for the moment) on a much older story — a story that significantly precedes agriculture as well as humans.

It is this older story that lies at the heart of truly deep differences, like those at play in the idiom “apples and oranges.” The contrast between these two fruits can be mapped according to many measures: taste, smell, texture, visual appearance, and so on. When used colloquially, the phrase serves as a proxy for unmanageable difference — to describe categories that differ along so many axes that they can no longer be meaningfully compared.

However, in evolutionary terms, the difference between apples and oranges is not ineffable. It is not a folksy aphorism or a Zen puzzle at which to throw up one’s hands. To the contrary, it can be temporalized and quantified; or at least estimated. In fact, in evolutionary terms, that difference comes down to about 100 million years. That is, at least, the date (give or take) when the last common ancestor of apples and oranges lived — a flowering plant from the mid-Cretaceous.

The best way to represent these deep stories is with a diagram called a phylogenetic tree. In a phylogenetic tree, each species is assigned its own line, and each of these lines is called a branch. Points at which two branches intersect represent the common ancestor of the species assigned to these branches.

Phylogenetic trees can serve many purposes. Their classical function is to communicate a hypothesis – a pattern of familial relationships supported by a particular set of data based on DNA sequence, fossils, or the physical characteristics of living organisms.

But here are two alternate reasons to build trees:

  • To inspire wonder
  • Or (my favorite) just because

To reflect these additional motivations – this conviction that trees are for everyone and for all occasions and that an evolutionary tree belongs on every street corner – when I build trees, I often avail myself of a range of non-traditional materials. I’ve written previously about creating edible trees using cake frosting and fruit, as well as building trees out of state symbols and popular songs. Now here are two additional building materials, which are arguably even more fun.

First: Stickers. This one is titled: “Like Apples and Oranges…and Bananas.”

Bananas split ways with the common ancestor of apples and oranges about 150 million years ago, 50 million years before the split between apples and oranges. On this tree, these relationships are represented like so: the banana branch diverges from the apple branch at a deeper position on the trunk, and the orange branch diverges from the apple branch at a shallower position. 

All of the data required to build this tree  (and essentially any tree) is available at TimeTree.orgOn TimeTree, select “Get Divergence Time For a Pair of Taxa” at the top of the page. This is where one can obtain a divergence time estimate for most pairs of species. The divergence time is an approximate date, millions of years ago, at which the organisms’ last common ancestors may have lived. For more heavy duty assistance, there is the “Load a List of Species” option at the bottom of the page. Here, one can upload a list of species names (.txt), and TimeTree will generate a complete tree – a schematic that can serve as a guide in patterning one’s own phylogenetic artwork.

Here, by way of additional illustration, are three more sticker trees, equally charming and equally mouthwatering:

Carrot, watermelon, broccoli, strawberry, and pear.

Onion, asparagus, tomato, cucumber, and cherry.

Raspberry, apricot, pea, grape, and green pepper.

Sticker trees are festive takes on traditional trees. They are brighter, livelier, and more lovely. But, like traditional trees, they are also 2D, restricted to a flat sheet of paper. To extend one’s phylogenetic art projects into three dimensions, one must modify the choice of materials. There are many options. The following 3D tree, for example, employs 13 pieces of plastic toy food, the accouterments of a typical play kitchen. Segments of yarn serve as branches.

Trees like these, made of stickers or toys, constitute playful takes on deep questions. In pencil and yarn, they sketch a network of primeval relationships. They tell the history of our foods, a narrative whose origins profoundly precede us, as well as our intention to selectively breed them. To the Way-Before, to the Way-Way-Way-Before, these projects give shape and color. If and where they succeed, it is because they manage to do two things at once: To communicate a vast biological saga extending across many millions of years, and to be completely cute. Perhaps best of all – and let it not go unmentioned – anyone can make them.

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Bio: Rachel Rodman has a Ph.D. in Arabidopsis genetics and presently aspires to recast all of art, literature, and popular culture in the form of a phylogenetic tree.

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Maize Anatomy and the Anatomy of a Maze

Commonly known as corn throughout much of North America, maize is a distinctive emblem of the harvest season. It is one of the most economically important crops in the world (the third most important cereal after rice and wheat) and has scads of uses from food to feed to fuel. The story of its domestication serves as a symbol of human ingenuity, and its plasticity in both form and utility is a remarkable example of why plants are so incredible.

The genus Zea is in the grass family (Poaceae) and consists of five species: Z. diploperennis, Z. perennis, Z. luxurians, Z. nicaraguensis, and Z. mays. Maize is the common name of Zea mays subsp. mays, which is one of four Z. mays subspecies and the only domesticated taxon in the genus. All other taxa are commonly and collectively referred to as teosintes.

The domestication of maize, apart from being an impressive feat, has long been a topic of research and a challenging story to tease apart. The current understanding is that maize was first domesticated around 9000 years ago in the Balsas River valley in southern Mexico, the main progenitor being Zea mays subsp. parviglumis. It is astonishing how drastically different in appearance teosintes are from modern day maize, but it also explains why determining the crop wild relative of maize was so difficult.

Teosinte, teosinte-maize hybrid, and maize - photo credit: wikimedia commons

Teosinte, teosinte-maize hybrid, and maize – photo credit: wikimedia commons

Teosintes and maize both have tall central stalks; however, teosintes generally have multiple lateral branches which give them a more shrubby appearance. In teosinte, each of the lateral branches and the central stalk terminate in a cluster of male flowers; female flowers are produced at the nodes along the lateral branches. In maize, male flowers are borne at the top of the central stalk, and lateral branches are replaced by short stems that terminate in female flowers. This is where the ears develop.

Ears – or clusters of fruits – are blatantly different between teosintes and maize. To start with, teosinte produces a mere 5 to 12 fruits along a short, narrow cob (flower stalk). The fruits are angular and surrounded in a hard casing. Maize cobs are considerably larger both in length and girth and are covered in as many as 500 or more fruits (or kernels), which are generally more rounded and have a softer casing. They also remain on the cob when they are ripe, compared to teosinte ears, which shatter.

Evolutionary biologist, Sean B. Carroll, writes in a New York Times article about the amazing task of “transform[ing] a grass with many inconvenient, unwanted features into a high-yielding, easily harvested food crop.” These “early cultivators had to notice among their stands of plants variants in which the nutritious kernels were at least partially exposed, or whose ears held together better, or that had more rows of kernels, and they had to selectively breed them.” Carroll explains that this “initial domestication process which produced the basic maize form” would have taken several hundred to a few thousand years. The maize that we know and love today is a much different plant than its ancestors, and it is still undergoing regular selection for traits that we find desirable.

Female inflorescence (or "ear") of Zea mays subsp. mays - photo credit: wikimedia commons

Female inflorescence (or “ear”) of Zea mays subsp. mays – photo credit: wikimedia commons

To better understand and appreciate this process, it helps to have a basic grasp of maize anatomy. Maize is an impressive grass in that it regularly reaches from 6 to 10 feet tall and sometimes much taller. It is shallow rooted, but is held up by prop or brace roots – adventitious roots that emerge near the base of the main stalk. The stalk is divided into sections called internodes, and at each node a leaf forms. Leaf sheaths wrap around the entirety of the stalk, and leaf blades are long, broad, and alternately arranged. Each leaf has a prominent midrib. The stalk terminates in a many-branched inflorescence called a tassel.

Maize Anatomy 101 - image credit: Canadian Goverment

Maize Anatomy 101 – image credit: Canadian Government

Maize is monoecious, which means that it has separate male and female flowers that occur on the same plant. The tassel is where the male flowers are located. A series of spikelets occur along both the central branch and the lateral branches of the tassel. A spikelet consists of a pair of bracts called glumes, upper and lower lemmas and paleas (which are also bracts), and two simple florets composed of prominent stamens. The tassel produces and sheds tens of thousands of pollen grains which are dispersed by wind and gravity to the female inflorescences below and to neighboring plants.

Female inflorescences (ears) occur at the top of short stems that originate from leaf axils in the midsection of the stalk. Leaves that develop along this reduced stem wrap around the ears forming the husk. Spikelets form in rows along the flower stalk (cob) within the husk. The florets of these spikelets produce long styles that extend beyond the top of the husk. This cluster of styles is known as the silk. When pollen grains land on silk stigmas, pollen tubes grow down the entire length of the silks to reach the embryo sac. Successful fertilization produces a kernel.

The kernel – or fruit – is known botanically as a caryopsis, which is the standard fruit type of the grass family. Because the fruit wall and seed are fused together so tightly, maize kernels are commonly referred to as seeds. The entire plant can be used to produce feed for animals, but it is the kernel that is generally consumed (in innumerable ways) by humans.

There is so much more to be said about maize. It’s a lot to take in. Rather than delve too much further at this point, let’s explore one of the other ways that maize is used by humans to create something that has become another feature of the fall season – the corn maze.

Entering the corn maze at The Farmstead in Meridian, Idaho

Exploring the corn maze at The Farmstead in Meridian, Idaho

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