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Comment by gus_massa | Hacker News Reader

I eat mango (10 per year?), but I never opened the shell of the seed. I thought it was the seed.

Does anyone know why the leaves are initially so dark and then become lighter? Is that common in plants?

> I eat mango (10 per year?), but I never opened the shell of the seed. I thought it was the seed.

The seed can be planted with the husk, but removing it speeds up the germination because the embryo can access light and water more easily.

I assume they evolved to have the inedible husk to prevent damage while being eaten and increase the distance from the original tree, effectively delaying germination. (If you can describe evolution as having an intention…)

Isn't there a movie about it, the incredible husk or something? Idk I'm not that into movies

The incredible hulk?

I liked the part where the husk turn green.

And bigger… you could say it grows…

Yes this is exactly it. Mangoes lost their megafaunal partners (giant sloths?) so they're evolutionary anachronisms

Relevant xkcd: https://xkcd.com/1259/

Giant sloths lived in South America, where they were the likely megafaunal partners of the avocado.

The megafaunal partner of the mango is probably the elephant, which is still extant in the native range of the mango.

https://blog.plover.com/bio/urushiol-2.html

Oh you're totally right. I forgot mangoes were from India. Thanks for the correction!

Many seeds need a dormancy period before germinating, and frequently a husk or germination-inhibiting coating (Tomatoes) surrounds the seed as a delay mechanism: the coating/husk has to rot before the seed gets contact with soil and water. For many it's way of ensuring that seeds don't germinate at the start of Winter. For others there's a (sometimes long!) maturation process that happens within the seed (Macadamias) before they're ready to sprout. Other times the husk is there to protect the seed while it goes through the gut of some animal (often birds) so that it gets transported well away from the parent plant.

Nature is pretty clever, imho.

Another example of a seed with long germination time is the coco de mer[1], coming in at 2 years. It also happens to be the largest seed of any plant.

[1] https://en.m.wikipedia.org/wiki/Lodoicea

On the other end of the spectrum there are many seeds with quick germination time but extremely long dormancy periods. Some of the biggest weeds in agriculture are plants whose seeds could last multiple decades in the soil until the right conditions show up

These plants usually evolve to serve a particular ecological niche. It's kinda like the soil's immune system. Exposing bare soil to direct sunlight is one of the most harmful things you can do to a soil ecosystem. So many plants evolved seeds that lay dormant until they're needed to come and protect the soil

Plants like dandelions are known as major weeds, but they only germinate in soils that are too compacted (e.g. a farmland with a history of plowing). These dandelions take over, decompact the soil, and then get "outcompeted" by other plants (usually perennials with longer lifespans).

I use scarequotes for competition because it's a good example of a natural system where "competition" is a lens of analyzing nature that could cause you to miss the bigger picture

> why the leaves are initially so dark and then become lighter? Is that common?

Yes. Red pigments are a common defense against cold and radiation. They are masked later by the green pigments.

Yes, generally dark colors absorb more light, and young leaves do not have any chlorophyll (so not green)

>Does anyone know why the leaves are initially so dark and then become lighter? Is that common in plants?

From what I've seen it's common in at least a subset of plants, that fresh leaves have a very distinctive red-ish colour.

> Does anyone know why the leaves are initially so dark and then become lighter? Is that common in plants?

I’ve noticed the same thing in frangipani. I assume it has something to do with the same amount of chlorophyll being distributed over a greater area, but that’s just a guess.

Also note that the leaves don’t just get lighter as they grow: the older ones also start to become dark again as they die.

Here is a guess.

Some nutritients / elements are rare and plants need to manage them carefully. That also means that they need to protect themselves against animals feeding on them. For that, they develop antifeedants [0] for example. Maybe plants develop the structure of leaves and antifeedants first before eventually loading it with chlorophyll [1] for which e.g. magnesium is required (no idea if that counts as rare but it is certainly harder to acquire than hydrogen, oxygen or carbon.

[0] https://en.wikipedia.org/wiki/Antifeedant

[1] https://en.wikipedia.org/wiki/Chlorophyll#Chemical_structure

I've grown avocados and it's a very similar process - the leaves of avocados also start dark and get lighter. Curiously, I had a fairly large inside plant that I set out during nice weather and it got "sunburned".

Sunburn is indeed the appropriate term. The plant is not used to the strong solar energy so it gets damaged. Most plants will do just fine if you gradually introduce them to more real sunlight.

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