Whenever you learn a new subject, you usually have to learn a new vocabulary as well. Sometimes it seems unnecessary. To take an example from the plant world, there’s the term blade, “the broad thin part of a leaf apart from the stalk.” This is the part most of us call the “leaf.” Why do we need another word for leaf?, you might ask.
Good question. Read through this list of terms and then ask yourself the question again. A leaf is much more complex than you might have thought! And soon you’ll find that using these 19 basic terms in an accurate way will make it easier to learn a new plant.
Nineteen brand new terms may sound like a lot. But we’ll break them down into five commen sense groups – stem, leaf parts, leaf types, leaf arrangements, the flower, and the inflorescence (flower cluster) – and they’ll be much easier to learn. By the way, you can click on any of the images to get a larger view.
Except where noted, definitions from the The New Oxford American Dictionary.
Let’s start with the stem, where leaves are attached.
1. Node: the part of a plant stem from which one or more leaves emerge, often forming a slight swelling or knob.
Why is it necessary to give this part of the stem a special name? Beyond the biological reason that there must be something special happening there in order for a leaf to “know” it must grow from this point, there is the convenience for us when we try to describe how leaves are arranged along a stem, which you will see when we look at leaf arrangement.
2. Internode: the part of a plant stem between two of the nodes from which leaves emerge.
I rarely use or see this term when trying to identify a plant, but it follows so logically from the definition of node that I thought it worthwhile to mention.
3. Bud: an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of the stem. (definition from wikipedia)
You’re probably already familiar with buds. In the illustration below, the bud is occurring in the “axil” of the leaf, which is the upper angle between the leaf stalk and the stem. Recognizing buds is important under two circumstances when trying to identify plants. 1) When you need to distinguish a bud from a “stipule” (the next term), and 2) When you need to determine whether a leaf is “simple” or “compound” (coming up!).
4. Stipule: a small leaflike appendage to a leaf, typically borne in pairs at the base of the leaf stalk.
The stipules shown here are more or less snug up against the stem and the leaf stalk (you may wish to click on the images to enlarge them and see the stipules more clearly). Stipules come in wildly varying forms, and not every plant even has stipules. They are good aids to identification, though, so look closely for them whenever you examine a new plant.
Plant-in-hand tips: nodes are where the leaves are attached to the stem – they will often be swollen. A bud will often be above the leaf stalk, will stick up from the stem and have a rounded top; a stipule may be in the place where you expect to see a bud, but it may cling to the stem, or it may be to the side of the leaf stalk – it probably won’t have the rounded top of a typical bud.
5. Blade: the broad thin part of a leaf apart from the stalk [the blade may be called a "lamina" in many technical references].
The part that I always (or used to) think of as a leaf is actually just one part of the leaf. I’m only defining two parts of the leaf – the blade and the petiole – in this exercise, but in the image below, you’ll see in smaller-sized text three other terms you may want to remember: apex = the tip of the blade; base = the end of the blade opposite the apex; margin = edge of the blade.
The blade, of course, is where most of the photosynthesis of the plant takes place. The petiole, besides being a way to keep the blade attached to the stem, carries nutrients and water to the blade. In the illustration below, the midvein, the major conduit to smaller veins that are distributed throughout the blade, is conspicuous. Veins deliver nutrients and water to every part of the blade and carry the products of photosynthesis back to the petiole to be delivered to other parts of the plant.
6. Petiole: the stalk that joins a leaf to a stem; leafstalk.
The word comes from the Latin petiolus, which means “little foot.” The petiole is the foot of the leaf, then, and the foot steps firmly on the stem.
Plant-in-hand tips: The relative length of the petiole and the blade can be important in identification – make note – is the petiole relatively long, or is it so short that it’s hard to find? Is the petiole absent altogether? This happens in some species where the blade itself attaches directly to the stem.
7. Simple: not divided or branched.
The thing to keep in mind, now, is that, by tradition, a leaf is attached to a stem. Each….leaf….is….attached….to….a….stem. Look at the next two illustrations closely, now:
On the left is a simple leaf. On the right it looks like you have three leaves attached to the stem. (Where on the stem, by the way, is the leaf attached? That’s right – at the node.) What we have on the right, though is an example of compound, or branched, leaves. We have one petiole, in this instance, and three leaflets. These leaflets look like blades, but they are really one blade subdivided into three parts.
8. Compound: consisting of two or more simple parts or individuals in combination.
Compound leaves may look like the illustration on the right, above, or they may look more like the leaves of a fern. The blades of a compound leaf are fully subdivided into leaflets. The Bean (or Pea) family has many examples of compound leaves. Take a look the next time you see a living bean or pea plant and see whether you can recognize the petiole and the subdivided blades.
Plant-in-hand tips: Can you guess the most surefire way to tell whether the leaves of a plant are simple or compound? Look for the bud! The bud will be on the stem, in the angle between the petiole and the stem. Click on the illustration at the right, above, and see if you can locate the small bud on the stem just above the compound leaf on the right.
9. Alternate: placed alternately on the two sides of the stem.
In an alternate arrangement, there will be only one leaf per node. In the illustration below, the even-numbered leaves are on the left and the odd-numbered leaves are on the right side of the stem.
10. Opposite: arising in opposed pairs, one on each side of the stem.
In an opposite arrangement, there are two leaves per node. In the illustration below, both leaves 1 and 2 arise from the same node.
11. Whorled: a set of leaves, flowers, or branches springing from the stem at the same level and encircling it.
In a whorled arrangement, there are 3 or more leaves per node. In the illustration below, 4 leaves arise from the same node.
12. Spiral: winding in a continuous and gradually widening (or tightening) curve, either around a central point on a flat plane or about an axis so as to form a cone.
In a spiral arrangement, we are back to 1 leaf per node. In the illustration below, the leaves corkscrew around the stem.
Plant-in-hand tips: Leaf arrangements are pretty straightforward to figure out. Just look for the nodes and then determine how many leaves are coming off each node. If there’s only one leaf per node, you need only determine whether the arrangement is alternate or spiral, and it’s usually pretty obvious.
So that’s it for basic leaf terms – twelve in all.
Now we’ll turn to the flower, which is one of the main reason humans pay attention to plants – the beauty of the flowers. To study the parts of the flower, I’m using a beautiful illustration from the Wikipedia Commons. I want you to see the entire image first, because of its excellent design. Then I’ll use a modified version, with the 9 basic flower terms you should learn right away.
Here’s the diagram with only the terms we are concentrating on.
Let’s think of the flower as a set of concentric rings. Let’s start from the outside ring.
Sepals are usually coarser than petals, which are usually soft and velvety.
Notice how these two definitions depend on each other. I still haven’t decided if it’s easier to think of a calyx as a group of sepals or to think of a sepal as a unit of the calyx. At any rate, the function of the calyx does seem to protect the petals and remaining parts of the flower when it is in bud. So when you see flower buds, you’re usually seeing the calyx.
Plant-in-hand tips: The calyx, with its sepals, forms the outermost layer of a flower. If you make it a habit to start with the outside of the flower and work your way in, you’ll find it easier to recognize those parts that are in the center.
15. Petal: each of the segments of the corolla [see next definition] of a flower, which are modified leaves and are typically colored.
When most of us think about flowers, it’s the showy petals we think of.
16. Corolla: the petals of a flower, typically forming a whorl within the sepals and enclosing the reproductive organs.
Again, notice how these two definitions depend on each other. Petals make up the corolla and the corolla consists of petals.
Plant-in-hand tips: Just as the calyx with its sepals forms the outermost layer of a flower, so the corolla with its petals forms the next layer of a flower.
On the right is a photograph from the Wikipedia Commons. You can see here that we’re starting outside the flower and working inward when we go from sepal to petal (and from calyx to corolla). Continue comparing this photograph with the drawing above as we work our way into the heart of the flower.
If you continue thinking of concentric rings, the next ring is that of the male reproductive parts. Most flowers have six or more stamens arranged in a ring around the female reproductive part. For now, if you remember that the anther contains the pollen and the filament supports the anther, that’s fine. For our basic plant identification, the term we’ll use most often, however, is stamen for the entire male part.
18. Pistil: the female organs of a flower, comprising the stigma, style, and ovary.
The innermost part of the flower is the female reproductive part. It is not a ring, but a solitary structure called the pistil. The stigma is like a mouth that takes in the pollen. The style is like a throat that carries the pollen down to the ovary, where the pollen fertilizes the eggs, or ovules. For basic plant identification, remember pistil for the entire female part.
Plant-in-hand tips: The descriptions of the concentric rings and the male and female parts are for “perfect” flowers, which indeed have both male and female parts. Some flowers have just one or the other. Stamens will always look different from the pistil, so if you have a flower with stamens but you cannot find an inner structure that’s different from the stamens, you probably have a male flower. If you find only one structure in the center, it’s probably a pistil and therefore you have a female flower.
19: Inflorescence: a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. A flower that is not part of an inflorescence is called a solitary flower (definition from wikipedia).
The “typical” flower that we looked at, and the illustration of the flower showing its sepals and petals, were solitary flowers. But many, many flowers occur in clusters called inflorescences. We won’t go into the different types of inflorescences just now. To give you an idea of what’s coming, though, here are some schematic drawings of inflorescence configurations from wikipedia. They are, from left to right, a spike, raceme, panicle, and umbel.
Plant-in-hand tips: If the flowers on a plant are small and clustered together, you probably have an inflorescence. Solitary flowers are usually larger than flowers found in an inflorescence. If you do have an inflorescence, look closely at the individual flowers within it. You’ll see that each of them is made up of the same parts of the flowers that we just looked at – and are arranged in the same concentric rings: calyx, corolla, male parts, female parts.
So there you have 19 basic botanical terms to help you start identifying flowers. Spend a few days looking at live plants with this guide. Soon you’ll be comfortable with all these terms and will be asking for more.