Thread by @PetitRmy1

It takes five (5) oaks to make a new oak. Why? My explanations (🧵)

A few days ago I asked the students the following question: how many oaks to make a new oak? It was during a lecture on pollination ecology. I defined an oak as any multicellular genetically unique organism made of oak cells. The answer is blowin’ in the wind.

Of course, they immediately thought about the two parental trees, the maternal and paternal oaks. Oak trees have both male and female flowers, so a single oak can give rise to a new oak following self-fertilization, but this is exceedingly rare.

My picture portrayed an oak seedling vigorously germinating, with the cotyledons still visible, ruling out vegetative propagation. So let’s count two oaks to start with.

These oak trees are in fact spore-producing plants, giving rise to the small spores in the stamens and to the large spores in the pistil. They are not gamete-producing plants. Therefore, you cannot compare them to humans, who need only two gamete-producing parents to make a baby.

One of the 2 gamete-producing oaks is well known: it’s the pollen, avtiny multicellular plant made of 2 cells, one of which will give rise to the pollen tube, the other to the 2 sperm cells. The female gamete-producing oak is also tiny, made of seven cells: the embryo sac.

The embryo sac remains attached to the mother plant, so we have a tiny plant within a plant, like Russian dolls. This makes four oaks so far.

Now one of the two sperm cells combine with the egg cell to produce a new embryo. This embryo is nourished at the expense of its (nearly) identical twin, the endosperm, which results from the fusion of the other sperm cell with two cells from the embryo sac.

Genetically, embryo & endosperm are identical, except that the endosperm is triploid: it has received a double dose of DNA from its mother and a single dose from its father. Never heard of endosperms before? You should if you ❤️ 🥖: wheat endosperm is ground into flour for bread!

This adds up to five genetically unique multicellular ‘oaks’ to make a new oak: two diploid ones (the spore-producing trees), two haploid ones: the gamete-producing ‘parents’, and one triploid: the endosperm, embryo’s twin, which will be sucked to death by its sibling.

In her recent book Vegetal Sex, @stella_sandford asks whether 'male' and 'female' really mean the same when applied to humans or trees, and whether the zoological categories of sex are really adequate for understanding the life cycle of plants.

After reading this thread, would you say that plants are awesome, cool, strange, bizarre, or exhausting?

Are plants:

In the poll I made on Twitter, most of the 77 participants suggested it takes 2 oaks to make a new one: there were only 4 correct answers (5) including at least 3 students that attended my lecture 😅

@UBordeaux_M2BFT @univbordeaux_EN @univbordeaux @INRAE_NA_BDX @BdxSciencesAgro @SocBotaniqueF @TelaBotanica @INRAE_France #botany #flowers #pollen #seed #angiosperm #floweringplant #iloveplants #iamabotanist #livingwithplants #plantslover #loveplants #ihavethisthingwithplants