A semi-technical description

Why a plant is described in a fixed order

Two botanists who have never met can describe the same plant in the same way. They use the same words, in the same order. This is called a semi-technical description. It uses plain words and a few technical terms.

A fixed order helps in three ways.

• Nothing is forgotten, because every part gets its turn.
• Two descriptions can be compared line by line.
• A reader who knows the order can find any fact at once.

The order of a description

A description has eight steps.

1. Habit. Is the plant a herb, a shrub or a tree? Does it live for one year or for many?
2. Root. A tap root, or a fibrous root?
3. Stem. Herbaceous or woody, erect or climbing, branched or not.
4. Leaf. Simple or compound, the kind of venation, and how the leaves sit on the stem.
5. Inflorescence. How the flowers are arranged: racemose, cymose, or a single flower.
6. Flower. The four whorls in turn: calyx, corolla, androecium and gynoecium.
7. Fruit and seed. The kind of fruit and the kind of seed.
8. Floral diagram and floral formula. The flower in a picture and in symbols.

Steps 1 to 4 give the vegetative characters, the parts that grow and feed the plant. Steps 5 to 7 give the floral characters, the parts that make seeds. Step 8 sums up the flower.

What to write at each step

Every step has a short list of choices. You met them in the lessons on the root, the stem, the leaf and the flower. Here is how to use them.

• Root: a tap root with its branches, or a fibrous root. A plant with parallel leaf veins usually has a fibrous root.
• Stem: say whether it is herbaceous or woody, and whether it is erect, climbing or creeping.
• Leaf: simple or compound, the venation, and the phyllotaxy, which is alternate, opposite or whorled.
• Inflorescence: racemose, where the main axis keeps growing and the youngest flower is at the tip, or cymose, where the main axis ends in a flower.
• Flower: say whether it has bracts, whether it is radial or has one plane of symmetry, and whether it is bisexual or unisexual. Then take each whorl in turn. The calyx is made of sepals, the corolla of petals, the androecium of stamens and the gynoecium of carpels. For each one write how many parts there are and whether they are free or united. For the gynoecium, also say whether the ovary is superior or inferior.
• Fruit and seed: the kind of fruit, and whether the seed has one seed leaf or two.

One plant described: mustard

Here is the mustard plant, written in the fixed order.

1. Habit: an annual herb.
2. Root: a tap root with branches.
3. Stem: herbaceous, erect and branched.
4. Leaf: simple and alternate, with net venation.
5. Inflorescence: racemose.
6. Flower: bisexual and radial. There are four free sepals in two pairs and four free petals. There are six free stamens and two carpels joined together, with a superior ovary.
7. Fruit and seed: the fruit is a long dry pod called a siliqua. It holds many seeds.
8. Floral diagram and formula: drawn and written in the next lesson.

Notice that every line answers one step, and no line mixes two steps. That is what makes a description easy to check.

Step through a description

Move the slider from step 1 to step 8. The bar shows how far you have come.

Try it in Python

The program holds the description of the mustard plant in a dictionary and prints it step by step, in the fixed order.

Practise with new numbers

Common mistakes

• Writing the flower before the root. The vegetative characters always come first.
• Skipping a step because the plant has no flower to hand. A full description covers all eight steps.
• Treating the formula as the description. The formula sums up one flower. It does not replace the words.
• Mixing two steps in one line. Keep the leaf and the flower apart.
• Using everyday words such as pretty or big. Use terms such as racemose, radial and superior.

Remember these

• A semi-technical description uses plain words and technical terms in a fixed order.
• The eight steps are habit, root, stem, leaf, inflorescence, flower, fruit and seed, and floral diagram and formula.
• Steps 1 to 4 are vegetative characters. Steps 5 to 7 are floral characters.
• The flower is described whorl by whorl: calyx, corolla, androecium, gynoecium.
• Step 8 sums up one flower in a picture and in symbols.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Name the two groups of characters in a description of a plant.

2. In which order are the vegetative parts described?

3. A botanist writes the word racemose. Which step is this?

4. Why do botanists keep the same order for every plant?