Big Leaves

The other day I idly noticed this leaf on the ground.

Breadfruit leaf on ground

Hmm, big leaf, I thought. It was from a young breadfruit tree (Artocarpus sp.) – I knew that. I simply hadn’t thought of breadfruit leaves as big before. There they are up in the tree. Once I looked, I realized that they are big.

Breadfruit tree
And so are a lot of other leaves around here. Yesterday I took a stroll with my camera and paid attention to leaf sizes.

Banana (Musa sp.).

Banana leaf and flower

Bijao, or Calathea lutea, in the same order, Zingerbales, as the banana.

Calathea lutea

Resurrection plant (Curcuma sp.), also in the same order as banana.

Curcuma

(Okay, I cheated on the last three images. They’re old ones from my iPhoto library, and the Curcuma is just now flowering, the leaves are not up yet. Everything else, though, really was photographed yesterday.)

“Elephant ear” (unidentified species).

Unidentified elephant ear

Cecropia sp.

Cecropia

Teak (Tectona sp.)

teak leaves

So, I started asking myself a question, the answer to which is really obvious to anyone who has studied ecology, but I needed to re-think it.

What I learned in ecology, and what I see for my own eyes every time I look for it, is that leaves of plants that grow in the shade tend to be bigger than the leaves of plants that grow in the full sun. The usual explanation is that a large surface area is needed to gather sufficient sunlight for photosynthesis when the intensity of sunlight is low.

Makes sense.

But I’m looking at these bananas growing in full sun. Likewise the Cecropia, which is a canopy tree, growing above all the other trees in my back yard “woods.” Likewise the breadfruit tree, the Calathea, the Curcuma. The only leaf that matches my idea of growing in the shade is the elephant ear. Possibly the teak, which is growing up in the woods, but there’s a teak farm not far from here and it’s out in the full sun. The trees are not shading each other at all, since the trees are tall and skinny.

So what’s the story?

These big-leafed plants are growing side-by-side with, or even above, average- or small-leafed plants.

I did a little scrounging around on the internet looking for an explanation, but all I found were statements like, “Big leaves are well suited to rainy climates, so many trees that grow well in rainy places have them.” With the added observation that in climates where there is a lot of rain, there is less sunlight than in climates where there is not much rain.

Well, okay. We do have a lot of rain in the rainy season (especially last year), but here in the savanna the forest is a “dry” forest, not a “rain” forest, so in that respect, I don’t think of here as a climate where there is a lot of rain.

One thing I have to remember, though, is that some of these plants are not really native to this area. Bananas, breadfruit, Curcuma, teak, no. The elephant ear, yes, and it is growing in the shade. I could assume that these non-native plants would rather be living in a rainier, more moist, and therefore more overcast, environment. So all these large leaves may be more useful in their native environment than they are here in this savanna, where we have at least two months of the year of very little or no rain.

That leaves Cecropia as the only real puzzle. Maybe it’s not such a puzzle, now that I think of it. Cecropia trees have very few leaves, and the ones they have drop off frequently. I’d bet that if I measured the entire surface area of the leaves of a Cecropia tree and compared it to the surface area of the leaves of its neighboring, but lower, trees, that the Cecropia would have a smaller total surface area than the trees below it.

Hmm.

Just some idle thoughts.

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About Mary

I spent a few years at sea, and I never came back from a cruise without having learned something new about the ocean or what lived in it. After retiring to Panama, I began to learn something new about the tropical savanna ecosystem nearly every day I stepped outside. I focused on plants, those marvelous signs of life. Now I'm in my second retirement, living in Sicily. I'm leaving my plant studies online for those who have found them useful.
This entry was posted in Ecology, PostAweek2011. Bookmark the permalink.

5 Responses to Big Leaves

  1. Look at your picture of Cecropia. Notice how the leaves fan out into a single layer of light harvesting surface area. If they had more leaves, the lower ones would be shaded by the upper, younger ones.
    Leaf size is a funny thing and does not conform to any simple rule. One way of looking at it is to ask if the leaves of any particular species are bigger in the shade than in the sun (usually true). But when you start comparing across flowering plants, things are a lot messier. A few understory plants have little leaves, and a few open growing plants have big ones. Perhaps a greater leaf longevity in the tropics allows a bigger leaf size in general because while the plant invests more per leaf, it pays off longer.

    • Mary says:

      Yes, you’re right about the possibility of upper leaves shading lower leaves in Cecropia. But doesn’t that happen in other trees as well?

      Regardless, thank you for commenting on leaf size in general. I’ve noticed the different leaf sizes on the same plant, especially in lianas, too, and I’ve seen the little leaves on some understory plants. Nature just doesn’t like to put things in tidy packages that are understandable to humans – at least that’s my guess here.

  2. And at the very next blog checked there’s an article on leaf heteroblasty and shading.

  3. Pingback: A Tree Story « H is for Happiness

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