There’s no such thing as a tree (phylogenetically)

There’s no such thing as a tree (phylogenetically)

So that you just’ve heard about how fish aren’t a monophyletic crew? You’ve heard about carcinization, the job whereby ocean arthropods convergently evolve into crabs? You verbalize you receive it now? Sit down down. Sit down down. Shut up. Listen. You don’t know nothing but.

“Trees” are seemingly to be no longer a coherent phylogenetic category. On the evolutionary tree of vegetation, trees are incessantly interspersed with issues that are fully, 100% no longer trees. This methodology that, as an example, either:

  • The classic ancestor of a maple and a mulberry tree turn out to be no longer a tree.
  • The classic ancestor of a stinging nettle and a strawberry plant turn out to be a tree.
  • And that’s magnificent for many trees or non-trees you can converse of.

I belief I had a quite magnificent wager at this, however the topic is a long way worse than I’m able to also maintain imagined.

CLICK TO EXPAND. Partial phylogenetic tree of various vegetation. TL;DR: Tan is certainly, 100% trees. Yellow is tree-treasure. Green is 100% no longer a tree. Sourced mostly from Wikipedia.

I realized after making this chart that tree ferns exist (h/t seebs), which I converse proper emphasizes my level additional. Also, h/t kithpendragon on LW for suggestions on rising accessibility of the graph.

Why enact trees withhold going on?

First, what’s a tree? It’s a mammoth prolonged-lived self-supporting plant with leaves and wood.

Also of ardour to us are the non-tree “woody vegetation”, treasure lianas (thick woody vines) and shrubs. They’re no longer trees, however finally to me, it’s quite obvious how a tree can also evolve proper into a shrub, or vice-versa. The confusing fragment is a tree evolving proper into a dandelion. (Or vice-versa.)

Wood, as it’s good to per chance also simply maintain guessed by now, is additionally no longer a particular phyletic category. But it indubitably’s an more affordable category – a lignin-dense structure, in total that grows from the exterior and that forms a quite readily identifiable self-discipline cloth when separated from the tree. (…Okay, no longer essentially the most explainable, however you understand wood? You know if you procure something in your hand, and it’s made of wood, and it’s good to per chance uncover that? Yeah, that thing.)

All vegetation maintain lignin and cellulose as structural parts – wood is plant subject that is dense with each and each of these.

Botanists don’t seem to converse it easiest can also maintain long gone one methodology – as an example, the classic ancestor of flowering vegetation is theorized to maintain been woody. But we additionally maintain quite sure evidence of up to the moment evolution of woodiness – verbalize, a brand new plant arrives on a quite barren island, and a number of the offspring of that plant becomes treelike. Of vegetation native to the Canary Islands, wood independently developed finally 38 times!

One relevant element is that each one woody vegetation enact, in a sense, start life as herbaceous vegetation – by and wonderful, a tree sprout shares one blueprint of properties with any herbaceous plant. Indeed, botanists name this form of elephantine, relaxed increase from the heart that elongates a plant “most critical increase”, and the later increase from towards the exterior which causes a plant to thicken is “secondary increase.” In a woody plant, secondary increase additionally methodology growing wood and bark – however other vegetation on occasion enact secondary increase as effectively, treasure potatoes of their roots.

This paper addresses the query. I don’t understand many of the closely genetic info, however my affect of its thesis is that: Analysis of convergently-developed woody vegetation display cloak that the genes for secondary woody increase are similar to most critical increase in vegetation that don’t enact any secondary increase – even in unrelated vegetation. And woody increase is an adaption of secondary increase. To abstract a little bit more, there is a classic and purposeful structure in herbaceous vegetation that, when a bit tweaked, “dendronizes” them into woody vegetation.

Dendronization – Evolving proper into a tree-treasure morphology. (Within the form of “carcinization“.) From ‘dendro‘, the extinct Greek root for tree.

Can this be tested? Yep – knock out a few genes that administration flower trend and trade the light stages to mimic summer season, and researchers found that Arabidopsis rock cress, a distinctly herbaceous plant vulnerable as a mannequin organism – grows a woody stem never in some other case considered in the species.

The tree-treasure woody stem (e) and morphology (f, left) of the gene-altered Aridopsis, in contrast to its distinctly non-tree-treasure accepted carry out (f, magnificent.) Photos from Melzer, Siegbert, et al. “Flowering-time genes modulate meristem determinacy and increase carry out in Arabidopsis thaliana.” Nature genetics 40.12 (2008): 1489-1492.

So no longer easiest can wood attach quite without hiss in an herbal plant, it goes to attain from messing with a number of the genes that withhold a watch on annual behavior – an herby plant’s frequent lifecycle of reproducing in warm weather, death off in frigid weather. So as that will get us two properties of trees immediately: woodiness, and being prolonged-lived. It’s mild a much explain from turning a plant proper into a tree, however additionally, it’s in reality no longer that a long way.

To ogle at it one other methodology, as Andrew T. Groover put it:

“Clearly, in the survey which genes attach a tree versus a herbaceous plant, it will seemingly be folly to ogle for genes contemporary in poplar and absent in Arabidopsis. Extra seemingly, tree forms converse variations in expression of a equivalent suite of genes to these display cloak in herbaceous relatives.”

So: There are seemingly to be no longer any unparalleled “tree” genes. It’s proper a unparalleled expression of genes that vegetation already exercise. Analogously, it’s good to per chance attach a cake with flour, sugar, eggs, sugar, butter, and vanilla. That it’s good to per chance per chance additionally attach frosting with sugar, butter, and vanilla – a subset of the substances it’s good to per chance also simply maintain already purchased, however in assorted ratios and exercise.

But again, the reverse additionally happens – a tree wishes to enact each and each most critical and secondary increase, so it’s quite simple for a tree lineage to tumble the “secondary” increase stage and stay an herb for its total lifespan, thus “poaizating.” As talked about above, it’s hypothesized that the earliest angiosperms maintain been woody, a few of which would maintain misplaced that in change into essentially the most familiar herbaceous vegetation lately. There are additionally some vegetation treasure cassytha and mistletoe, herbaceous vegetation from tree-heavy lineages, who’re each and each parasitic vegetation that grow on a bunch tree. Gleaming fully nothing about the evolution of these lineages, I converse it’s life like to speculate that they each and each came from a tree-treasure ancestor however poaized to change into parasites. (Evolution is amazingly engrossing in parasites.)

Poaization: Evolving into an herbaceous morphology. From ‘poai‘, extinct Greek term from Theophrastus defining herbaceous vegetation (“Theophrastus on Herbals and Herbal Therapies”).

(I make an apology to anybody I’ve ever complained to about jargon proliferation in rationalist-diaspora blog posts.)

The trend of staying in an earlier stage of trend is in total identified as neotenizing. Axolotls are an example in animals – they resemble the juvenile stages of the closely-associated tiger salamander. Did you understand very infrequently, or when exposed to hormone-affecting substances, axolotls “grow up” into something that looks loads treasure a tiger salamander? Not unlike the gene-altered Arabidopsis.

A accepted axolotl (left) vs. a spontaneously-metamorphosed “adult” axolotl (magnificent.)

[Photo of normal axolotl from By th1098 – Own work, CC BY-SA 3.0, Photo of metamorphosed axolotl from deleted reddit user, via this thread: ]

Does this mean something?

A chum requested why I turn out to be so drawn to this discovering about trees evolving convergently. To me, it’s that a tree is this kind of neatly-diagnosed, on a typical basis thing. You know birds? Agree with if in reality there maintain been amphibian birds and mammal birds and insect birds flying all the blueprint in which via, and so all of them looked quite worthy the identical – feathers, beaks, little claw ft, the lot. You had to be a proper bird expert with a thought to uncover an insect bird from a mammal bird. Also, most of us don’t know that there isn’t proper one trend of “bird”. That’s what’s occurring with trees.

I turn out to be additionally drawn to culinary applications of this recordsdata. You know of us who receive all excessive about “don’t you understand a tomato is a fruit?” or “a blueberry isn’t in reality a berry?” I turn out to be one once, it’s k. Listen, neglect all of that.

There could be a trend of botanical definition of a fruit and a berry, speaking about which parts of classic plant anatomy and reproduction the structure in query is derived from, however they’re certainly no longer associated to the culinary or classic understandings. (An apple, arguably essentially the most central fruit of all to many folk, is doubtlessly no longer a botanical fruit either).

Let me be very sure right here – mostly, that is no longer what biologists treasure to reveal. After we verbalize a bird is a dinosaur, we mean that a bird and a T. rex fragment a classic ancestor that had recognizably dinosaur-ish properties, and that we are able to customarily level to some these properties in the bird as effectively – feathers, bone structure, no subject. That it’s good to per chance per chance analogize this to equivalent statements it’s good to per chance also simply maintain heard – “a whale is a mammal”, “a spider is no longer an insect”, “a hyena is a pussycat”…

But that is no longer what’s going on with fruit. Most “fruits” or “berries” are seemingly to be no longer descended from a classic “fruit” or “berry” ancestor. Citrus fruits are all derived from a classic fruit, and so are apples and pears, and plums and apricots – however an apple and an orange, or a fig and a peach, enact no longer fragment a fruit ancestor.

In attach of searching to receive uppity about this, can also simply I counsel the following:

  • Acknowledge that each one in every of our categories are unparalleled and a little bit arbitrary
  • Witness wistfully of photos of Welwitschia
  • Ship a fruit basket to your native botanist/plant evolutionary biologist for hanging up with this, or change into one yourself
While natural different is continuously belief to easily be an ongoing job with no “targets” or “stop parts”, most scientists take into consideration that life peaked at Welwitschia.

[Photo from By Sara&Joachim on Flickr – Flickr, CC BY-SA 2.0, ]

Some more nice looking findings:

  • A mulberry (left) is no longer associated to a blackberry (magnificent). They proper… each and each did that.
[ Mulberry photo by Cwambier – Own work, CC BY-SA 4.0, Blackberry photo by By Ragesoss – Own work, CC BY-SA 3.0, ]
  • Avocado and cinnamon are from quite closely-associated tree species.
  • It’s you can converse of that the ultimate classic ancestor between an apple and a peach turn out to be no longer even a tree.
  • Of particular ardour to my Pacific Northwest readers, the Seattle neighborhood of Magnolia is misnamed after the native madrona tree, which Europeans perplexed with the (equivalent-taking a leer) magnolia. In actuality, these two species are easiest very distantly associated. (Yow will stumble on them each and each on the chart to envision precisely how a long way apart they are.)
  • None of [cactuses, aloe vera, jade plants, snake plants, and the succulent I grew up knowing as “hens and chicks”] are associated to each and each other.
  • Rubus is the genus that contains raspberries, blackberries, dewberries, salmonberries… that trend of thing. (Be acutely aware, a genus is the category proper above a species – which is trend of a made-up distinction, however suffice to reveal, that is a closely-associated groups of vegetation.) A pair of of its members maintain 14 chromosomes. A pair of of its members maintain 98 chromosomes.
  • Seriously, I’m going to hand $20 in money to the following plant taxonomy expert I meet in person. God is aware of bacteriologists and zoologists don’t must take care of this.

And I in reality maintain one more unanswered query. There doesn’t seem to be a receive have a tendency of vegetation evolving into grasses, no subject the truth that grasses are quite sufficient and seem trend of treasure essentially the most anatomically simple plant there will seemingly be – root, mammoth leaf, little flower, you’re magnificent to gallop. But most grass-treasure vegetation are in the identical crew. Why don’t more vegetation evolve towards the “grass” system?

Let’s receive non-public for a 2nd. One of my philosophical takeaways from this venture is, clearly, “convergent evolution is a hell of a drug.” A 2nd is something treasure “taxonomy is no longer automatically a monumental category for traditional utilization.” Phylogenetics are fully charming, and I enact wish of us understood them better, and doubtlessly “there’s no such thing as a fish” is an efficient meme to maintain around on story of most of us enact no longer take into accout that they’re genetically closer to a tuna than a tuna is to a shark – and “no such thing as a fish” invitations that inquiry.

(That it’s good to per chance per chance, finally, verbalize that a tree is a technique. Wood is a technique. Fruit is a technique. A fish is additionally a technique.)

At the identical time, I in reality maintain this vision in my thoughts of a intellectual individual that takes this meandering essay of mine and goes around asserting “did you understand there’s no such thing as wood?” And they’d be trend of magnificent.

But on the identical time, insisting that “wood” is no longer a purposeful or understandable category would be essentially the most fascinatingly noxious rhetorical gallop. Criminal the head of selecting the curiously abstract over the honest appropriate total. A high-quality occasion of missing the forest for – uh, the forest for …

… Fail to bear in mind it.


Timeless Slate Superstar Codex / Astral Codex Ten half: The categories maintain been made for man, no longer man for the categories.

In direction of the stop of writing this half, I discovered that proper botanist Dan Ridley-Ellis made a tweet thread about this topic in 2019. Sight that for more treasure this from any individual that is aware of what they’re speaking about.

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