Why do some leaves have serrated edges ?

[Igor Suman]

What is the advantage of a serrated edge on a leaf over a smooth edged leaf ?

i.e. what is the purpose of these serrations ?.

[Martin]

What is the advantage of a serrated edge on a leaf over a smooth edged leaf ?

i.e. what is the purpose of these serrations ?.

 

that is an interesting question! I'd like to learn the answer too. Skye or Mokele will probably know. If nobody answers, it would be worth writing email to PZ Myers.

 

I will do a google search with "serrated leaf evolution" and see if anything obvious comes up.

 

BTW Igor here is a non-expert GUESS: caterpillars eat leaves. Some of them begin eating the leaf at the EDGE. it is easier to bite an edge than out somewhere in the middle, so the caterpillar evolves this program of starting at the edge.

 

MAYBE MAYBE a serrated edge can interfere with the caterpillar's program of behavior and confer a slight advantage this way

 

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another guess is that "compound" leaves with branching veins evolved from many smaller simple leaves, and these compound leaves naturally started out with a serrated edge

and there was simply no DISadvantage to getting rid of the serration

 

so you could say that the plants didnt require any evolutionary pressure to produce serration----it just happened accidentally in the process of MERGING LOTS OF SMALLER SIMPLE LEAVES TO MAKE ONE BIG ONE

and then there was no pressure to make the serration go away, so it just remained

 

one article I read said that compound leaves have evolved many different times in many different species of plant

 

leaf growth is controlled by relatively few genes so it is easy for a plant to mutate back and forth between many separate simple leaves in a group----on the one hand----and one single large serrated leaf taking its place----on the other hand.

 

that paper was by an evolutionary geneticist named Champagne IIRC, you might see it if you google

"leaf serrated evolution"

 

thanks for the intriguing question!

[Sisyphus]

Good question, and I would add, what's the advantage of few, large leaves vs. lots of small leaves or compound leaves. I'm guessing it's related to climate, but I don't really know.

 

I'll also put forward the guess that, as far as the serrated edge thing goes, there really is no advantage one way or the other, and that it's just the remnant of separate but more or less parallel evolution.

 

OR maybe serrated edges are in the midst of evolving from compound leaves, OR they were compound, but only evolved to the point where there's no advantage either way.

[ecoli]

Perhaps it has something to do with increased surface area? That's my best guess.

[Mokele]

Sorry, no idea.

[swansont]

Is there some division of relation between smooth- and serrated-leaf groups? i.e. do serrated-leaf plants more closely related to other serrated-leaf plants?

[bascule]

Is there some division of relation between smooth- and serrated-leaf groups? i.e. do serrated-leaf plants more closely related to other serrated-leaf plants?

 

There may be a common ancestry among certain groups of serrated leaf plants. However, there are also those where serrated and smooth edges appear within the same species, such as aspen.

[CurvKyle]

could it be to scare off predators? kind of like thorns

[Edtharan]

Serrated edges can have many reasons for evolving.

 

Sometimes it is to deter predators. A leaf with a serated edge and small spines would cause damage to the mouth of a herbivore and even just animals moving past it (there are some plants in Austraila - and I expect in other countries too - where just brushing past some of these can tear the skin open and cause bleeding - I have had it happen to me and it is like a big paper cut ).

 

Another reason is the control of water running off the leaf. The serrations can help scatter the water over a larger area and so stop too much water running off in one place and causeing erosion around the roots of the plant.

 

These are just 2 that I can think of off the top of my head, but there probably is as nearly many reasons as there are plants with serrated edges.

[CanadaAotS]

could it be to scare off predators? kind of like thorns

 

*cuts CurvKyle with his serrated leaf*

 

Yah, like to see a herbivore come near this baby...

[Glider]

Edtharian is right. In plants that have serrated leaves (but no spines) the serrations help with water runoff.

 

You will find that in wetter areas, plant have evolved a number of methods for keeping the leaf surface free of pooling water. For example , some have evolved a waxy or shiny leaf surface that repels water.

 

Other have developed pinate leaves where each leaf is divided into many smaller 'leaflets' extending from the petiole (in wet areas these are usually longer, e.g. Arecaceae Chamaedorea: the parlour palm). These leaflets are usually channelled to encorage water to run off.

 

On larger single leaves, serrations encourage the water to form drops at the edge and to fall off the leaf.

[Igor Suman]

What is the advantage of a serrated edge on a leaf over a smooth edged leaf ?

i.e. what is the purpose of these serrations ?.

 

Thank you everyone for your responses to this question.

 

One possible answer which has not been suggested is aerodynamics.

A leaf with a serrated edge would create more turbulance in the air flowing over it, (compared with a smooth edged leaf), the serrations would cause the leaf to flap more.

Perhaps there is an advantage to leaf flapping ?.

[GutZ]

What about a growth defect?

[gcol]

Here is a simplistic laymans observation:

 

A leaf is a rather simple growth system. Nutrients are carried to the extremities (growing edges) by veins. Is it unreasonable for growth to be most pronounced nearest to the veins? I suggest the topography of vein growth dictates leaf shape. Vein growth takes priority, leaf shape follows as it may. Some shapes may by chance suit certain niches, encouraging odd shapes. Veins first, shape second.

[jeskill]

Thank you everyone for your responses to this question.

 

One possible answer which has not been suggested is aerodynamics.

A leaf with a serrated edge would create more turbulance in the air flowing over it' date=' (compared with a smooth edged leaf), the serrations would cause the leaf to flap more.

Perhaps there is an advantage to leaf flapping ?.[/quote']

 

Increased air turbulence decreases the boundary layer above the leaf. This allows the leaf to be more efficient at coupling its temperature with the air temperature. A useful attribute for either cooling the leaf down or making sure the leaf temperature doesn't drop below air temperature (for example, at nighttime at high altitude).

[JHAQ]

http://www.earthandtable.com/glossary/plants/anatomy/leaf.html gives MANY leaf shape terms but does not say why . Interesting question