A day in the life of a cactus flower

Since this is the season for many cacti to flower, I’ve been spending a lot of time observing and photographing these marvels of the plant kingdom. As is the case with many other flowering plants, most cacti flowers are open during the day and closed at night. I’m going to illustrate this cycle with a cactus I bought a couple of weekends ago at the Carmichael Cactus & Succulent Society Show and Sale.

The cactus came labeled as Rebutia haugeana although a Google search produces no results. I don’t know exactly what it is, but it’s beautiful, and that’s all I care about.

 

From about 6 p.m. until 8 a.m. the flowers of this rebutia look like this:

From 6 p.m. until 8 a.m.

At 9 a.m. they slowly begin to open.

9 a.m. and 3 p.m.

At 10 a.m. they’re open half way.

10 a.m. and 4 p.m.

By noon, they’re open completely, and they stay that way until about 4 p.m.

From 12 p.m. until 4 p.m.

From 12 p.m. until 4 p.m.

After 4 p.m., the flowers slowly begin to close. By 6 p.m. they’re completely closed.

I did a little bit of research, and this is what I found out: If flowers are pollinated by insects active during the day (most flowers), the flowers are open during daylight hours. If they are pollinated by nocturnal insects (like the Queen of the Night cactus in this post), they are open at night.

So why don’t flowers stay open all the time? It is to save resources, especially pollen that might blow away or get wasted otherwise during times when pollinators are not active.

The opening and closing mechanism is triggered by changes in light or intensity or temperature. Cells in the flower expand or contract, causing the flowers to open or close. This behavior is called “nyctinasty.” What a great word to impress your friends with!

Curiously enough, many cactus flowers are wide open from about 12 a.m. to 4 p.m. and then start to close although at that time both the light intensity and the temperature are at their highest. I wasn’t able to find a convincing explanation, but most likely it is to prevent the loss of water from evaporation. This would make an interesting elementary or junior high school research project, and I’m going to suggest it to my younger daughter who will be participating in her school’s 6th grade science fair next year.