(the little one making all the noise is Stormy, an adult storm-petrel who seemingly has a faulty navigation system and comes to this cahow/bermuda petrel nest every year instead of to his breeding range further north. As far as he’s concerned this is his nest, the cahows disagree!)
Along that vein (that xylem? :p), let’s talk about angiosperm reproduction! (As always, if I mess up, tell me! This is all for me studying.)
Angiosperm reproduction is mostly sexual. Gametes are deposited on another flower (well, hopefully another one for the sake of genetic diversity.) Some are entirely sexual, some entirely asexual, many both.
Some forms of asexual reproduction are vegetative reproduction and apomixis. Vegetative reproduction is making a new individual from another non-flower part of the plant. Differentiated plant cells can de-differentiate more easily than fully differentiated animal cells. Some plants use the leaves for this, like this beautiful plant!
Other plants use special underground structures to make new versions of themselves. These aren’t roots - they’re really more like stems, but underground! We call them rhizomes. A new plant from root tissue is called a sucker. That leads to aspen forests like this one.
There’s also apomixis (‘without mixing") - it’s like parthenogenesis in animals. An embryo is made without sex - eggs are already diploid. There is no meiosis in the megaspore mother cell.
Why would asexual reproduction be a good thing? Well, for one thing, it increases fitness - if you’re already perfectly adapted, sexual reproduction will mess that up for you. If one genotype works, here you just make a lot of it, and then you’re set! (for now)
But then why sexual reproduction? The genetic diversity is helpful long-term. Say that environment your asexually reproducing plant was perfect for changes a lot, and it no longer works. Sexual reproduction would ensure there’s a chance one genotype will work now.
Pollination is the most important sexual reproduction strategy in flowering plants. There are a couple of main types - animal and wind pollination.
With animal pollination, you have to attract your pollinators, and animals want a reward. This doesn't have to be a real reward if they think it’ll be one.
This plant attracts wasps! It smells like a female wasp - so male wasps come and try to mate with it. This doesn’t work out, except for the plant, which puts pollen onto him. He’ll fly to another plant and try again - and he’ll pollinate that one! (image source here)
You have to signal that rewards are present. This is why flowers are so beautiful! And finally, you have to get the pollen onto the pollinator. Animal pollinated plants generally have less pollen per flower.
Wind pollination does not make flowers with sepals and petals - they’re not colourful and pretty. That would waste energy for these plants, which just want to make more pollen. They make tons of pollen per flower, because with wind, most of it’s not going to go anywhere near the right place.
So now that we’ve gotten those choices down, let’s say our plant has pollinated another plant successfully. A plant baby is coming! How does this work?
A zygote divides into two cells, then four, and so on. Eventually you’ve got two parts - an embryo with its callose coat (prevents chemical signals from coming in, actually!) and the suspensor (basically the umbilical cord - get sugar from parent). This becomes an embryo, cotyledons, and a seed coat down below (from parental tissues). Cotyledons are “seed leaves” - they store food and are the very first surface that does photosynthesis for the plant!
All of that wrapped together makes a seed. The first part of the shoot apical meristem is actually here! So now, we have our baby plant, but what are we going to do with it? We have to get it somewhere! It’s probably in a fruit with lots of other seeds.
Again, we have a few choices! Unsurprisingly, they’re wind and animal dispersal, with the addition of water dispersal! Wind dispersal leads to beautiful “engineering” like this.
…or the wings on this maple seed! (Image source here! Has other examples of seeds dispersed various ways. Warning for trypophobia a little while down.)
Animal dispersal either sticks to the animal with burrs or some such thing, or tastes good enough that they eat it and…disperse the seeds at a later time.
Water dispersal is cool! Basically, seeds float on water till they reach dry land. Coconuts might be an example of this. (Another warning for trypophobia: a lot of water dispersal plants, like water lilies and lotus seed pods, have lots of holes. Don’t look up water dispersal, because one of the first images on Google is a lotus seed pod.)
So that’s about it for angiosperm reproduction! Hope you enjoyed it :)
