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Confounded Compounded Leaves

18 Oct

John and I visited the woods yesterday and watched an ant crew complete with supervisors, guards, overachievers, and slackers hauling bits of fungus and winged pine seeds along a 10 foot trail (= 5 ant-miles).   They extract the core from the pine seeds and ditch the wing. The size of the pine seed relative to an ant is about like an airplane wing relative to a poodle. And now on to native plants.

The forms and functions of leaves may be boring, but boring is my middle name. So today’s topic is boring compound leaves. To talk about a topic we better define it. My Webster’s Collegiate Dictionary defines compound leaf as…..Dontcha just hate presentations that start like that!?

Here is a single compound leaf on Gumbo Limbo, with 5 leaflets. The leaf ends in a leaflet. (All photos today by John Bradford)

Here is a single compound leaf on Gumbo Limbo, with 5 leaflets. The leaf ends in a leaflet. (All photos today by John Bradford)

A compound leaf is a single leaf that looks misleadingly like a stem with multiple small leaves.   The small fake leaves are called leaflets. Now ask, what’s the difference? Most leaves, compound or not, drop free as single units. A stem-leaf junction is always immediately below a bud, but a leaflet revealingly has no bud.  A stem ends in a bud, but the compound leaf stalk ends in a leaflet or it just peters out budless. Examples of compound leaves are plenty. A vegetable gardener says green beans.   A suburban landscaper might cite Schefflera. A fruit fancier could think of starfruit. Stonewall Jackson may mention hickory. Teenagers behind my fence know of marijuana. Those who loath invasive exotics lie awake over Brazilian Pepper. Native plant enthusiasts have umpteen examples. Enjoy a dozen:

  • Ash
  • Paradise Tree
  • Hercules Club
  • Wild Lime
  • Torchwood
  • Elderberry
  • Most ferns
  • Coontie
  • Poison Ivy and Poisonwood and Poison Sumac
  • Milk Pea, Cow Pea, Butterfly Pea, Rosary Pea, Partridge Pea, Sensitive Pea
  • Bay Beans, Coral Beans, Velvet Beans, Cool Beans
  • Things that stick in my socks (Spanish Needles, Tictrefoils)
This Sesbania has about 9 compound leaflets visible, each leaf with numerous little elliptic leaflets.

This Sesbania has about 14 compound leaves visible, each leaf with numerous little elliptic leaflets.

And there exist twice-compound leaves. Huh? Ones where the leaflets themselves are “compound leaves.”   Fact is, a leaf can be twice, thrice, or more compound.   Think of some frilly ferns, or native Nickerbean. This all leads into nomenclature we shall ignore.

This Royal Fern has a twice-compound leaf. Only one leaf is in this photo. It is

This Royal Fern has a twice-compound leaf. Only one leaf is in this photo. It is “doubly compound,” divided into about 12 main subunits, these subdivided into numerous smaller units.

Compound leaves have evolved separately many times in numerous unrelated plant groups. Many more plants have lobed leaves approaching compound, but not quite.

Lobed and almost compound.

Lobed and almost compound.

Some species have a portion of the leaves simple (simple = not compound), with other leaves on the same individual lobed or compound. Red Mulberry, Calloose Grape, Marsh Mermaid Weed, and the invasive exotic Arrowhead Vine come to mind. The mix reveals different pros and cons of different leaf forms depending on the leaf’s age, position, or physiological state.

Mulberry simple leaves.

Mulberry simple leaves.

Mulberry lobed leaves.

Mulberry lobed leaves.

Bald Cypress pretends to have compound leaves in a converse fashion. Its branchlets with many small leaves behave like single “compound leaves” in the sense of being seasonal, flat, and deciduous.

As Miami botanist Steve Woodmansee recently commented on this blog, there’s an evolutionary two-way street.   Although clearly simple leaves have evolved many times into compound leaves, the reverse occurs too. A locally familiar example of compound-to-simple is Coin Vine, a Legume uncharacteristically having simple leaves.

There must be something compelling to induce “big” simple leaves to subdivide over evolutionary time into “small” more or less separate leaflets and lobes.   Many botanists have wondered why, and several answers exist, none of them “the” single revealed truth.

Clammyweed. Each leaf with 3 narrow lobes.

Clammyweed. Each leaf with 3 narrow lobes.

First off all, it might seem optimal for a leaf to be as big as an umbrella and just steal all light from competitors below.   We have solar panels on our campus as big as patio surfaces. Not many plants however evolve umbrella leaves. There must be advantages toward small independent blades.

First disadvantage of big leaves: they fray and tatter in the wind, and are “expensive” to replace.

Second disadvantage of big leaves: bright sun exposes a leaf to more light than it can handle. Too much light diminishes photosynthetic ability and generates often unwelcome heat. On average, any leaf can use only about 20% of full sunlight. A big umbrella shadowing all below is wasting 80% or more of the incoming light while suffering possible damage.   A plant is usually better served by having vertically layered smaller leaves (or leaflets or lobes) capturing collectively far more than that original 20% at the top layer.  Light becomes more diffuse deep in the shadowed understory, so that the varied orientations of the leaves, leaflets, and lobes, and their flutterings allow more efficient capture of dim light, also light angling in at dawn and dusk, and sporadic bright “sunflecks” as the wind fleetingly parts the canopy above.

Frangrant Eryngo with some fancy lobes.

Frangrant Eryngo with some fancy lobes.

Third disadvantage of big leaves: Growth is not limited by light alone.   Every third grader knows, I hope, that leaves take in bad carbon dioxide and give us good oxygen. Breezes blowing across small leaves, leaflets, or lobes are more effective at gas exchange than those passing over large surfaces.   Bigger surfaces have more surface-breeze friction. Also, the margins tend to be younger fresher tissue. It is easy to show as a classroom demonstration more photosynthesis happening near the margins than “inland.”

Fourth disadvantage of big leaves:   As foliage absorbs solar energy it doesn’t merely photosynthesize, it heats up, and heat stress can be trouble. Without protective adaptations leaves would sometimes be hotter than the surrounding air, but they have evaporative cooling. Small blades shed water vapor and heat directly to the air better than big leaves. (By the way, on cold clear nights leaf blades can be colder than the surrounding air so that the ability of smaller blades to conform to air temperatures might sometimes help at both ends of temperature stress.)

One thing I like about compound leaves is the ability for individual movement by the leaflets.   Leaf movement in response to built-in rhythms and to environmental cues, including light vs. dark, is fascinating, especially in complex compound leaves.

In Pigeon Pea the leaflets can all move in unison, resembling the blades in venetian blinds. You see it in the time lapse below experiencing the end of a day, the night, and waking up the next morning:  CLICK to see the pea

In the following time lapse through a semidark night and the morning after, the Trefoil (left) and Oxalis (right) have individual leaflets all doing their own dance. (The classroom lights come on a couple times early in the evening— cleaning crew/security guard.)  CLICK

Inkwood compound leaf with 4 leaflets

Inkwood compound leaf with 4 leaflets

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14 Comments

Posted by on October 18, 2015 in Compound Leaves

 

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14 responses to “Confounded Compounded Leaves

  1. FelicityRask

    October 18, 2015 at 12:06 pm

    That was quite an ‘enlightening’ lesson. Now I can finally admit that I have had answered my mainly puzzled thoughts (well, most of them) over compound and single leaves. I hope you noticed the Oxalis single leaf wave around 10PM!
    Felicity Rask – still in VA

     
  2. George Rogers

    October 18, 2015 at 12:19 pm

    Thanks Felicity, Friendly isn’t it? Maybe it waved at the cleaning crew, coming in after 9 pm classes end.

     
  3. Chris Lockhart

    October 18, 2015 at 1:31 pm

    George, nice descriptions and photos. I especially liked the time lapse. Very cool, indeed! A colorful compound leaf in the fall I like to watch for is poison ivy. Easier to avoid. 🙂

     
  4. George Rogers

    October 18, 2015 at 3:45 pm

    Hi Chris, Too bad p.i. makes a person scratch, because I like the plant otherwise. Been 20 years since I’ve had any trouble with it…don’t know if that amounts to vigilance, luck, or lost sensitivity. Tried an experiment rubbing some on my arm and escaped unrashed. Saw some pretty fall color VA Creeper Friday too. Not like a trip to North Carolina though!

     
  5. Rosie

    October 19, 2015 at 8:11 am

    Loved the time lapse video! I had no idea that plants moved in the dark,

     
    • George Rogers

      October 19, 2015 at 10:33 am

      They really do, though the largest movements are at dawn and dusk. What I want is infrared “night vision” to catch them in “total” darkness. With the camera iso set extremely high (3200) and with exposures extremely long (many seconds), and then enhancing “exposure” to the limits on the computer later it is possible to get ghost pictures of leaves under fairly dark conditions. A moon-lit night provides more than enough light. A dark night with no moon is the very limit of how far you can stretch with “regular” equipment so far as I can tell. The pictures in the blog were taken overnight on a windowsill with a dim light on in the room. They seem brighter than they actually were because of that high iso, super-long exposures, and follow-up adjustments.

       
  6. Amy Fisher

    October 25, 2015 at 8:59 pm

    I often wondered about the pros and cons of compound leaves versus simple leaves. The pictures are absolutely beautiful and the explanations were great. Though big simple leaves are more visually impressive the compound ones are more efficient for the plant in most cases.

     
    • George Rogers

      October 25, 2015 at 9:32 pm

      Hey Amy, I saw a fun experiment today where a professor at Duke Dr. S. Vogel cut out the shapes of a relatively large sun leaf (on an oak) and a much-lobed shade leaf and covered them with heat-sensitive paper that turns different colors at different temperatures, showing how the lobed leaf cooled down more effectively.

       
  7. Shakeva J

    October 25, 2015 at 11:15 pm

    I learned that compound leaves come in varies shapes and forms. Compound leaves can be hairy, bumpy and or smooth. I thought that compound leaves was only one type of leave, but now this website have given me more insight on different types of plants that have compound leaves. So, I definitely agree on the pro and cons of compound leaves because you really have to pay attention to detail because no matter the shape or form it can be a compound leave. The pictures showed me how different the leaves can be,but they still have something in common Compound Leaves.

     
    • George Rogers

      October 26, 2015 at 10:22 am

      Hi Shakeva, Nice to see you! And thank you for noticing the “big picture” side of the post—that things plants do are always more diverse than we expect…even if we’ve been studying them for a few decades.

       
  8. My An Le

    October 26, 2015 at 1:56 pm

    I couldn’t find the time lapse video; maybe it’s because I’m on a Mac. I saw the camera set-up in the back of the class and was very curious as to what it would capture. Regardless, reading this post made me realize that plants are so diverse, yet so similar. I’ve learned so much about compound leaves and was so intrigued that I completed my own independent research about it. In contrast to your mentioned disadvantages, I’ve learned that there are also some advantages to having compound leaves that are worth sharing.
    1. Plants with compound leaves have longer petioles, which enable them to receive more direct sunlight to ease the process of photosynthesis. In addition, plants that grow in shaded areas need to have longer petioles near the bottom and shorter ones at the top to create less shade over the entire plant. (https://kb.osu.edu/dspace/bitstream/1811/1452/1/V05N07_340.pdf)
    2. Compound leaves have also proven to aid in air exchange. Herbivore damage to the plant also decreases when there are compound leaves. (http://www.plantphysiol.org/content/127/4/1533.full)

     
    • George Rogers

      October 26, 2015 at 3:04 pm

      My An, Thanks so much for adding to the content! Great points. I guess one big petiole at the base of the leaf plus whatever little stalks the leaflets have gives the blade more control and more “stretch.” Having more edge/surface helps in air exchange and in other exchanges, such as heat, too. If you place leaves upside down in shallow warm water with some baking soda for CO2 you can see, by bubbles, more air exchange along edges. The herbivore damage point is new o me! I like it.

       
  9. Daniel Lowenthal

    October 26, 2015 at 1:59 pm

    Huh, I never realized that the smaller compound leaves at the bottom were scattered spread out like that to capture the light that did get through

     
    • George Rogers

      October 26, 2015 at 2:59 pm

      Well, there are lots of factors in play, the thing with the scattered light though is that a tall vertical system of small fluttery blades, compound leaf leaflets, or lobes, or merely small leaves has many advantages in terms of overall light capture, gas exchange, and temperature regulation.

       

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