Comment by photochemsyn | Hacker News Reader

Comment by photochemsyn | Hacker News Reader

Humans care about wood, so they made tree (thing which produces wood) a category, as it can be used to build bridges, ships and other structures. Wood being dense also made it a better feedstock for charcoal (one can use grass, however).

As far as why trees don't seem to evolve into grasses, (or grasses into trees), it might be all about C3 vs C4 carbon metabolism, the latter being a complex structural system that pre-concentrates atmospheric CO2 before feeding it into the photosynthetic biochemistry (which is the right way to do artificial photosynthesis as well). This is apparently difficult to do in trees?

https://pubmed.ncbi.nlm.nih.gov/32409834/

> "Since C4 photosynthesis was first discovered >50 years ago, researchers have sought to understand how this complex trait evolved from the ancestral C3 photosynthetic machinery on >60 occasions. Despite its repeated emergence across the plant kingdom, C4 photosynthesis is notably rare in trees, with true C4 trees only existing in Euphorbia."

And here we have the world's largest Euphorbia:

https://www.wikidata.org/wiki/Q5851367

>As far as why trees don't seem to evolve into grasses

There is obviously no non-teleological answer for this, but it can be much much more straight forward than metabolism.

Think of plants as basically solar panels. We can think of the 'grass' phenotype as competing through r-type selection. Lots and lots of individuals, lots of surface area, short life cycles. Short bursty growth, convenient loss resilience, easy mobility.

'Trees' are the also optimizing for surface area (among other things), but are relying on k-type selection. Longer life-cycles, lower probability of successful reproduction, specialized pollinators, and very significantly, vertically stratified growth habit. Being an individual in a k-type species is like a very significant advantage for that individual, since its unlikely that the vast majority of k-type seeds will successfully reproduce.

Being k-type may not be more competitive for the species overall, but it may result for a selection bias at the individual member resolution, and so may be unlikely to be selected against.

There are many many advantages to lignification when your whole thing is basically being solar panels on a pole. It would seem extremely unlikely this has anything to do with metabolism other than 'doing more of it'. We already know why monocots don't make trees more significant than palms (read: vascular bundles and eusteles). My money goes to species level versus individual level selection in k versus r.

Lots of trees are wind pollinated. It's one of the reasons pollen season can be unpleasant.

When I see the ground under an oak tree covered in acorns, most of which will be food, my first thought is definitely not that the tree is engaging in k-selection.

The tree relies on squirrels to disperse the acorns (hiding them and then forgetting where they were buried, or being eaten by a grue before retrieving the acorns).

Fruit is another common way to disperse seeds. Animals & birds eat the fruit, and then disperse the seeds with a dollop of fertilizer (poop).

Lots of co-evolution going on.

Well, yes, that's all true, but I was specifically addressing the claim "trees are k-selectors".

The big split between flowering plants is between monocots (grass, palm trees) and dicots (say a Rose bush and a Apple Tree.)

You can find non-trees and trees that are monocots and dicots and also non-flowering trees and non-trees for that matter. The main issue is that when plants get big they get woody and take on the characteristics of trees.

I like the irony of that title that a "tree" (in the computer science sense) is the basic unit of phylogeny with the caveat that it is broken at the top because the three operating systems for a cell are described here

https://en.wikipedia.org/wiki/Domain_(biology)

they do show a tree on that page based on a particular set of genes but if you picked a different set of genes you would get a different tree because complex cells have a mixture of Archaea and Bacteria because they merged in some horizontal gene transfer event long ago.

Bamboo being the obvious exception of a grass that really wants to be a tree.

And Palm "Trees".

Palms are not grasses.

Is that true? Most of the internet says they are, and I first learned it from a local guide several years back.

Per Wikipedia, under the clade commelinids there are 4 orders:

Arecales (palms)

Commelinales (spiderwort, water hyacinth)

Poales (grasses, rushes, bromeliads)

Zingiberales (gingers, banana)

So depending on how you measure, palms and "grasses" are distinct but closely related groups of plants.

All grasses are monocots (single part seeds) - https://en.wikipedia.org/wiki/Monocotyledon and its got things like corn, oats, lawn grasses, wheat, horsetail grass ... and sugar cane, bamboo, Joshua trees, and palm trees.

>As far as why trees don't seem to evolve into grasses, (or grasses into trees)

They are different branches of the tree of life. Dicots (trees) vs monocots (grasses)

Palm Tree is monocot, and it is a notable tree. A lot of grasses are dicot, any one with ornate leaves (monocots have blade-like leaves).

Palm tree is not very useful for structural wood.

Bamboo is monocot, not a tree, and is highly useful for structural wood. These are all orthogonal.

Only with a lot of glue added or as entire culms

Tell the pacific islanders that.

Idk if you've dealt with palm wood but most of it is very very soft. You would not want to try to do anything you would recognize as structural framing with it.

I have and as long as we count coconut lumber it's suitable for low-rise structures.

Being structurally a tree and producing useful wood are two distinct things.

But a palm "tree" is not structurally a tree -- it does not have branches.

Completely beside the point, but coconut lumber is used for structural applications. The trees need to be fairly mature though.

>Palm Tree is monocot, and it is a notable tree

The least tree-like tree ever

>A lot of grasses are dicot

Such as?

Clover is a grass and dicot. Is clover a tree?

How tall are you?

Clover is grown on lawns...not sure how many people would call it a grass

Most people?

No? My guess would have been "zero people", for the obvious reason that clover isn't grass.

Wiktionary doesn't even list a sense for "grass" that would include clover, and anyone can just add glosses there.

How do you call all the short-lived, green dicots growing in the meadows?

Depends. What are you referring to? "Dicots" is not a category with any significance.

Grass is mostly characterized by having blades instead of leaves. Other plants would be called... whatever they're called. If you want a generic term, it's "plants".

If you want a term that refers to the specific function of covering what would otherwise be bare earth, that term is "ground cover", but ground cover is not restricted to plants. It applies just as well to gravel.

I'm confused. If you know clover is different from the green stuff with narrow leaves that grows in lawns, but you call clover grass, then what do you call the green stuff with narrow leaves?

"Grass" as well.

It's on the lawn, it's green, it's not a weed. Therefore, it's grass. ;)

By this criterion a rosebush is "grass".

Nah. Clearly a bush or tree, unless it's still just at grass height. :)

Sorry, was the rosebush off the lawn, not green, or a weed?

I don't know, you seem to be the expert. You tell me. :)

Is pine a tree? Cedar? Fir? Magnolias? How about cabbage?

Conifers (pine, cedar, fir) are trees but neither dicot or monocot, so outside the scope of this question.

Magnolias are trees and dicots (so expected).

Cabbage is a dicot but not a tree - not all dicots are trees. Maybe you misinterpreted my parent comment as me suggesting all dicots were trees? I more wanted to illustrate the key difference between grasses (which are monocots) and most trees

Cabbage is an interesting item in that list...

I give you the Jersey cabbage https://en.wikipedia.org/wiki/Jersey_cabbage

> The Jersey cabbage (Brassica oleracea longata) is a variety of cabbage native to the Channel Islands that grows to a great height and was formerly commonly used there as livestock fodder and for making walking sticks. It is also known as Jersey kale or cow cabbage, and by a variety of local names including giant cabbage, long jacks, tree cabbage and the French chour and chou à vacque.

> The 'Jersey cabbage' develops a long stalk, commonly reaching 6 to 10 feet (1.8 to 3.0 m) in height, and can grow as tall as 18 to 20 feet (5.5 to 6.1 m). ...

https://www.atlasobscura.com/articles/jersey-kale

Rosewood is similar, I believe.

I'd give even odds that brassica oleracea could be bred into a tree, yes.

Brassica oleracea longata

Is green a color? There is a continuous set of colors between green and blue, but when I see a green I often know it.

My wife and I disagree quite strongly on the crossover point fairly consistently. I also saw some research showing a supposed gender gap in that observation. Whether or not the gender part is true it seems very much that different people crossover some of these at different points.

Have you considered evolutionary selection as reason for c4 not being adapted by trees?

Grasses profit much more from growing quick than trees, where new opportunities (e.g. trees dying, fires etc) are rather rare & being able to grow extremely quickly wouldn't provide much of a benefit?

> ... being able to grow extremely quickly wouldn't provide much of a benefit?

After any substantial ground clearing event (eg bushfire, etc), wouldn't the subsequent "winners" be those who grew the fastest to capture the available sunlight + suppress their competitors?

There are multiple waves of succession in trees.

So no, being the first does not give you a clear advantage.

https://en.m.wikipedia.org/wiki/Ecological_succession

So true. I live in an area that was clearcut a century ago. The battle of the first movers vs the usurpers is well underway if you know what to look for. It's a fight to the death, in very very slow motion.

Thanks, that's interesting. :)

If tree is a category, does it have limits?

came here for the grassy tree, not entirely disappointed.

Reply on news.ycombinator.com