Succulents in Sweaters

The discussion over on Facebook:

Jim Bishop: Thanks for the name, Aeonium canariense. There was one in the garden when we moved here and I never knew the name. There are many more now.

Jan Emming: OK, you’ve yet again tripped my professorial side. Fuzziness and hairs can serve several functions based upon the needs of the plant. One is indeed cold protection, especially in plants that have some winter snow or chill because they are at high altitudes or latitudes. This usually manifests as wool right at the apex, which is where the dividing cells are, and those are the most sensitive and the most important for the growth of the plant. Wool also helps protect against extreme heat and sun, and hides small developing fruits from being eaten until they are ripe enough to push forth and release seeds.

Plants with hairy leaves (not woolly terminal apices) usually have this because the hairs help scatter light and reflect it away from the cells so that the plants won’t overheat. That reflectiveness, combined with whiteness or other pale colors and insulation value, helps keep leaves cooler than they would otherwise be, and prevents sunburn. Leaf hairs also reduce air circulation right at the leaf surface, which helps reduce water loss.

So as you can see, hairiness can serve multiple functions for the plants, based upon the habitat and ecological demands on the plant involved. Hope that helps you understand them a bit better.

Oh, and they are definitely beautiful features too. Not to overlook that either.

Jim Bishop: Don’t some of the super hairy cactii from the fog areas of South America use the hairs to condense the fog and drip the moisture at the roots of the plant?

Jan Emming: Jim gets a gold star for making a point that I forgot!

Jim Bishop: Not sure why Aeonium canariense has fuzz. It burns easily and does best in partial to full shade. They might be to trap moisture too since they are also from a foggy area. It isn’t white, so doesn’t reflect light.

Frederique Lavoipierre: Aren’t some hairs also glandular, such as on sundews, and attract (and dissolve!) insects, or is that different? And do some hairs serve as a mechanical, and sometimes chemical, defense against predation? Do I remember something from my plant biology days about trichomes on tomatoes?

Jan Emming Frederique: You are correct that there are more types of hairs or projections on leaves of other species, but they tend to perform very different functions from the hairs on succulents.

Frederique Lavoipierre: I have a great book on plant adaptations that I am now inspired to go upstairs and retrieve. I didn’t know that hairs on succulent plants are defenses against abiotic factors, and that they don’t have these other types of hairs. Plants are endlessly fascinating to me. But then, so are insects

Susan Gaul: Excellent thread! Thanks Debra for prompting it. Plants stay in one place and so evolved amazing ways to grow, reproduce and survive.