Leaf Shape: Margins, Venation and Position

In last week’s blog I discussed simple vs compound leaves and basic leaf shape.  This week I tackle  margins, different venation patterns, and key ways that leaves are attached to the stem. The terms discussed are in bold text. The examples are all illustrations I’ve done over the years.  If you find any mistakes feel free to tell me; I’m not a botanist, just a keen and interested amateur..

What is a margin?

A margin refers to the edge of the leaf.

Entire margins

A smooth edge is called an entire margin.  There are no teeth or notches taken from the edge, it’s smooth and complete.  An example is the beech.

Lobed leaf margins

There are lobed margins, where the blade of the leaf is divided into protrusions.  These can be spiky or rounded (so think of a dandelion and an oak leaf).

These protrusions either come from the midrib (as with the dandelion and oak) and are described as pinnately lobed; or they spread like fingers from a hand (think of a maple or ivy leaf); then the term is palmately lobed.

Toothed leaf margins: 3 types

Another margin type is toothed.  This covers three terms; serrate, dentate, and crenate.  Serrate margins are leaf margins where the teeth are like those of a saw, continuous and forward pointing (like the sweet chestnut).

Dentate margins have continuous teeth which point outwards (like the strawberry).

Crenate margins are pretty much the same as dentate ones, but the teeth tend to be rounded.  This is the case with this Golden opposite leaved saxifrage.

More on leaf margins…

This has covered some basic aspects of leaf margins.  For more please follow the link to the University of Rochester’s informative illustrated article.

Below is an illustration done for Rodale’s 21st Century Herbal by Michael Balick.  So this shows many of these margins on one page.

Venation Patterns on leaves

Venation patterns are the layout the network of veins form.  When you’re drawing a leaf you need to notice this, both in terms of getting the leaf looking correct, and also because it helps when plotting in shadows and lights.

The three types of venation: 1. Palmate Netted

There are three main types of venation.  The first is netted venation, where the leaf veins form a lace-like skeleton of veins.  This can be palmate netted venation, where the veins spread form one central point like fingers from a hand (think of a nasturtium or geranium).

Three types of venation: 2. Pinnate netted venation

Leaves often show pinnate netted venation; the more familiar pattern that you might see in a holly, or beech leaf skeleton; and you can see it in this honeysuckle study.

Three types of  venation: 3. Parallel venation

The other layout of veins has them running parallel to each other.  Members of the lily and onion (Allium) family show this, so do grasses.  Here, parallel venation is illustrated with the autumn crocus.

Phyllotaxy: How a leaf is attached to the stem

There’s a term to describe the way the leaves of a plant are attached to the stem: phyllotaxy, which directly translates from the latin as “leaf order”.  This is a wild and wonderful subject, and maths figures heavily.  The reason for the variation in leaf layout is both environmental and innate in the plant; so generally the purpose is to maximise the amount of sunlight hitting the leaf surfaces of a plant (and thus maximising space available for photosynthesis).

Phyllotaxy: Opposite leaf arrangement

Leaves can be arranged opposite one another at a node, in pairs.  This is, conveniently, called opposite.  Mint plants and maples show this pattern, like many of the plants in this plate I did for HarperCollins flower guide.

Phyllotaxy: Whorl leaf attachment

Leaves can also be arranged in a whorl, when more than two leaves appear at one node.  Bedstraws, like this ladies’ bedstraw show this pattern of phyllotaxy.

Phyllotaxy: Spiral leaf attachment

The most interesting arrangement, perhaps, is the spiral.  This relates to the Fibonacci sequence and the golden ratio. It can be seen in many aspects of nature (and not just in the plant kingdom).  However, I’m no mathematician, so the above link below will be better at explaining this than I could ever hope to be.

Spiral phyllotaxy means that the leaves (or pairs of leaves) are stepped around a stem, much like the steps of a spiral staircase.  This is always easier to see if you look directly down on a plant from above.  You’ll also note how infrequently leaves overlap or block each others’ access to the light.

The simplest form of spiral phyllotaxy has every third leaf aligned with one below it.  Grasses do this, as does the elm tree.

Another version has every fourth leaf aligned; but the commonest is probably the arrangement where every sixth one is in line with one (far) below it.  Oaks, cherries, apples, pears, and poplars show this.  I believe it also occurs in the damson, but it’s hard to tell from a side view.

In conclusion….

I think that’s plenty of botany for now (and my head’s spinning).  I do think that bearing these matters in mind is important when drawing a botanical subject.

Many thanks to Botany: A Textbook for Colleges by Hill, Popp & Grove from which much of this material is taken.

You may not need the terminology down perfect, but you do need to think about the following: 1. leaf arrangement on a stem.  2. margin form  3. venation.  It will improve your illustrations because (inevitably) it increases your understanding of a plant, and that’s what it’s all about.

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