BCSS - Forum

When we sow seeds most germinate as we sow under optimal conditions. We go on to keep the ones we like most. Those are probably not the ones that would have survived in habitat where only a few seeds of the same lot would have germinated and only the fittest would have survived. The fittest in habitat are most likely not the same specimens as the fittest (read: selected by us to be kept) in our seed trays.

Human selection is different from natural selection. That is how we eventually get cultivars that would never have survived in the natural world.

Kees wrote: ↑Sun Jul 04, 2021 6:31 am When we sow seeds most germinate as we sow under optimal conditions. We go on to keep the ones we like most. Those are probably not the ones that would have survived in habitat where only a few seeds of the same lot would have germinated and only the fittest would have survived. The fittest in habitat are most likely not the same specimens as the fittest (read: selected by us to be kept) in our seed trays.

Human selection is different from natural selection. That is how we eventually get cultivars that would never have survived in the natural world.

But what I am saying is that seed collected from solitary habitat plants has produced seedlings that cluster at an early age, all of them, every single one, no human selection involved at all.

Is it possible to prevent it happening? Maybe I'll buy a packet of Aylostera seed next year, (it doesn't look like I'll be able to go to Argentina again for a while) and see if I can keep them single headed by starving them. I doubt it.

I'm guessing that if you decapitate an old single headed Rebutia pygmaea in habitat and then grow that head in cultivation, the head will quickly offset as opposed to staying single?

Nick_G wrote: ↑Sat Jul 03, 2021 7:26 pm But why does a cactus that is single headed in habitat cluster in cultivation? Why should more water and nutrients provoke this? If it was as simple as that they all would do it and they don't.

Plants vary in their expression of apical dominance which is related to the amount of hormones produced by the apical meristem which in turn suppresses the lateral buds that have the potential to form branches. This is largely genetically determined so for instance a Rebutia will branch early in optimal growing conditions whereas a Ferocactus will not branch unless something damages the apical meristem turning off the supply of hormones. Size of the plant has an influence too so for example an Oreocereus will branch from the base once it has got tall enough for the lateral buds at the bottom to escape the apical meristems dominance. So it’s a combination of environment and genetics

Ali Baba wrote: ↑Sun Jul 04, 2021 9:38 am

Nick_G wrote: ↑Sat Jul 03, 2021 7:26 pm But why does a cactus that is single headed in habitat cluster in cultivation? Why should more water and nutrients provoke this? If it was as simple as that they all would do it and they don't.

Plants vary in their expression of apical dominance which is related to the amount of hormones produced by the apical meristem which in turn suppresses the lateral buds that have the potential to form branches. This is largely genetically determined so for instance a Rebutia will branch early in optimal growing conditions whereas a Ferocactus will not branch unless something damages the apical meristem turning off the supply of hormones. Size of the plant has an influence too so for example an Oreocereus will branch from the base once it has got tall enough for the lateral buds at the bottom to escape the apical meristems dominance. So it’s a combination of environment and genetics

Thanks, that's helpful and it also answers my next question as to why some cacti offset when the crown is damaged.

You can see extreme examples of the genetics at play in other members of the plant kingdom; for instance in some palms there is a single huge apical meristem and side shoots are never formed, even if the palm is decapitated; conversely in various tropical trees apical dominance is barely present and all the lateral buds develop immediately they are mature enough. Cacti show a range of possibilities in the middle of the spectrum.

Nick_G wrote: ↑Sun Jul 04, 2021 8:37 am Maybe I'll buy a packet of Aylostera seed next year, (it doesn't look like I'll be able to go to Argentina again for a while) and see if I can keep them single headed by starving them.

What about also trying some mostly buried in a substrate with similar optical properties to their natural habitat? It could simply be that the light hitting the sides of the plant (or in some plants the ratio of red to near infra-red) over-rides the apical dominance in the lower parts of the plant. Is the habitat substrate totally opaque or partially translucent?

In our conditions you might have to build in a damp-proof course at the level of the base of the stem and put the plants in your best lighting situations.

Bushy plants (like tomatoes) from potentially crowded situations use the ratio of red to near infra-red to sense whether they need to grow straight up to out-compete other plants surrounding them or if they have plenty of space and light around them to branch out. I can see several possibilities for this adaptation in a buried cactus. For example, if the soil has eroded away from the plant it might develop branches to stabilise the soil or expand its reach across the surface for potentially producing new roots.