Why Crocus Flowers Open for the Sun

So quickly, the Snowdrops (Galanthus nivalis) have passed their peak, but I cannot be sad. Their flowers will last a while longer, and in the meantime the Crocuses are stepping up to the plate.

Clumps of Tommy Crocuses in the Sidewalk Border

In my garden, these are mainly Crocus tommasinianus, or Tommy Crocuses. Tommies have a limited color range (mainly purple), but many consider them more resistant to rabbits and other evil garden vermin. Certainly, that has been my experience.

Tommies opening wide for the sun.

I have a strong childhood memory of a patch of Crocuses near my parents’ house. Every March I would look for them on the way to school. When they bloomed I always felt a little jolt of happiness. And so I have a soft spot for Crocuses to this day.

Some white non-Tommy Crocuses.

Anyhow, yesterday Judy went out to take pictures of the garden, including the Crocuses. It was a day of mixed clouds and sun, and I was a little anxious that Judy catch these flowers while the sun shone, as they are likely to close up when it is overcast.

Which made me wonder: why and how is it that Crocuses (and tulips and many other flowers) close up in the absence of light?

Nyctinasty at work – Tommies closing up. Look at the second picture to see the difference.

A little internet research revealed an answer, or at least a scientific name for the phenomenon: nyctinasty. Nyctinastic flowers close up in the dark either by pumping water out of cells at the base of the petals, or by growing new cells on the outside of the base of the petals, which forces them shut. To open, they grow cells on the inside.

Not sure if these yellow Crocuses are opening or closing.

To be honest, it’s not completely clear to me how this mechanism works, but I’m willing to believe that it does.

It’s impossible to know for certain why flowers engage in this behavior (isn’t it odd to think of flowers having behaviors?). The most popular theory is that nyctinasty evolved to protect pollen from dew or rain. Apparently wet pollen is not as attractive to pollinators and/or is not as conducive to pollination.

The other thing that I wonder about: couldn’t they come up with a better name for this phenomenon than nyctinasty? It sounds like something very unpleasant. More evidence that botanists need to hire marketing consultants to review all their naming decisions.


57 Comments on “Why Crocus Flowers Open for the Sun”

  1. While my Tommies were flowering, we had some very dull overcast days, but warm days, and the flowers opened wide. I did a post about it at the time as I was thinking that they opened by temperature and not by the sunshine. The bees were flying when we had the warm days and the flowers were open ready for them.

  2. Interesting to learn about the opening and closing of some flowers….. such a complicated process going on beneath these lovely bulbs. I agree about the name, sounds terrible. I love your crocuses by the way, I think I have neglected this bulb along the way…

  3. Our native bloodroot (Sanguinaria canadensis) closes at night and stays closed on cloudy days to protect its pollen. Ever since I learned this, I’ve paid closer attention to those that open and close and it seems a number of the short-lived, early spring bloomers fall in this group.

  4. I don’t know, Jason…when they let those marketing folks choose names, they can come up with some pretty dorky doozies. Fun info, and another wonky term that will never come up in polite conversation.
    Isn’t it delightful how the sight of something like a crocus can carry us back to childhood?

  5. I do like all your crocus, especially the yellow ones, it’s just struck me that mine are all white, purple and blue.
    How fascinating to learn how flowers actually open and close! I’m with you re the word though…..sounds dodgy! I still love cherry blossom as it reminds me of my childhood.xxx

  6. Flowers that do this really rely on their pollinators. I bet you have noticed all the bees on them. Honeybees get a jump on the season with them. In fact, I see more honeybees than the early native bees getting nectar and pollen. Did you ever notice pumpkin flowers that close at night? Sometimes a squash bee gets stuck in them overnight and is dead by the next morning since the flower only lasts one day. I have looked for bees in crocus, but never found one from the night before. The honeybees are a lot smarter, plus the flower will open and let them out anyway.

  7. Nyctinasty sounds like an STD. I love crocus, too, although I have no idea what the names of any of mine are. They’re all just ‘the crocus’ and seem to be fine with their status in the chorus instead of lead singer. Spring without crocus would be horrible.

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