Further to last week’s blog on illustrating botanical subjects, and the discussion of simple vs compound leaves and basic leaf shape; this week I thought I’d tackle leaf 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; and if you find any mistakes feel free to tell me, I'm not a botanist, just a keen and interested amateur..
Leaf margin refers to the edge of the leaf. 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.
There are lobed margins, where the blade of the leaf is divided into protrusions, either spiky or rounded (think of a dandelion and an oak leaf).
These protrusions either come from the midrib of the leaf (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) in which case the term is palmately lobed.
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, as with this Golden opposite leaved saxifrage.
This covers 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, due to be published later in the year, which shows many of these margins together.
Venation patterns are the layout the network of leaf veins form. When you’re drawing a leaf you need to notice this, both in terms of getting the leaf looking correct, but also because it helps when plotting in shadows and lights. 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 leaf).
Leaves often show pinnate netted venation; the more familiar pattern that you might see in a holly, or beech leaf skeleton; or as you can see it in this honeysuckle leaf study.
The other layout of veins has them running parallel to each other along the length of the leaf. Members of the lily and onion (Allium) family show this, as do grasses. Here, parallel venation is illustrated with the autumn crocus.
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, where maths figures heavily. The reason for the variation in leaf layout is both environmental and innate in the plant; generally the purpose is to maximise the amont of sunlight hitting the leaf surfaces of a plant (and thus maximising space available for photosynthesis).
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.
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.
The most interesting arrangement, perhaps, is the spiral. This relates to the Fibonacci sequence and the golden ratio, and can be seen in many aspects of nature (not just the plant kingdom). However, I’m no mathematician, and although it intrigues and interests me enormously, 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 (and 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 leaf 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.
So I think that’s plenty of botany for now (my head’s spinning); but 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 leaf arrangement on a stem, margin form, and venation on a leaf. It will improve your illustrations because inevitably it increases your understanding of a plant, and that’s what it’s all about.
Category: Biological terminology | Comments: 4 | Viewed: 17210
Hi Lizzie - this post is fantastic. So helpful! It was interesting to me that you said the beech has an entire margin. I was just on a walk yesterday looking at some beech trees and I thought, no they are serrated! Turns out, the American Beech (Fagus grandifolia) has serrate margins and the European Beech or Common Beech(Fagus sylvatica) has the smooth margin. So I learned even more than I thought! :) Thanks again for another great post. Carol
Thank you Lizzie, this is really clear and helpful. Portia
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