Morphology of Flowering Plants · Lesson 10 of 11
Floral Descriptions and the Solanaceae Family
“Construct a scientific plant description and connect floral symbols with the diagnostic characters of Solanaceae.”
• Describe a flowering plant in a consistent vegetative-to-floral sequence. • Interpret symbols for floral whorls, symmetry and fusion. • Recognise diagnostic vegetative and floral features of Solanaceae. • Explain how a floral diagram and a written description complement one another.
Why scientific descriptions need a fixed order
Two students can describe the same plant in very different words unless they agree on a sequence of observations. Botanical descriptions therefore begin with overall habit, then vegetative characters such as roots, stem and leaves, then the inflorescence and flower. The flower is described whorl by whorl, generally from the outer sepals through petals and stamens to the carpels. Fruit and seed characters complete the picture. This sequence prevents important diagnostic details from being forgotten and makes one species easier to compare with another.
A good description does not simply say 'green leaves and red flowers.' It tells whether the leaves are alternate or opposite, simple or compound, stipulate or exstipulate, and whether venation is reticulate or parallel. For flowers it specifies symmetry, sex, merosity, sepal and petal fusion, positions of stamens, ovary position, carpel number and placentation. These are reproducible structural characters rather than impressions of overall beauty.
Reading and constructing a floral formula
A floral formula compresses several characters into recognised symbols. K represents the calyx, C the corolla, A the androecium and G the gynoecium. P is used for perianth when sepals and petals are not readily distinguished. Br indicates the presence of a bract. The radial-symmetry sign ⊕ denotes an actinomorphic flower; bilateral symmetry is often marked by a separate zygomorphy sign. A bisexual sign combines male and female sex symbols. Numbers indicate the number of organs in each whorl, and parentheses show fusion of members within that whorl.
For example, K(5) indicates five fused sepals while K5 would describe five free sepals. C(5) indicates five fused petals. A5 means five stamens; whether they attach to petals must be explained or marked through an adhesion convention in a fully detailed formula. G(2) denotes two fused carpels. The ovary's superior or inferior position is conventionally shown with a line over or under G; because such typographic placement can be lost in plain text, always state the ovary position explicitly in the associated explanation. Never infer the number of ovules directly from the number written after G.
A schematic top view of a flower showing the number, arrangement and relationships of floral organs and the position of the mother axis.
A floral diagram often puts the mother axis towards the top as a small dot. The outer circles represent calyx and corolla; stamens are shown within; carpels occupy the centre. Unlike a short formula, a well-drawn diagram can show relative positions and attachment arrangements. Unlike a diagram alone, the full verbal description can include habitat, stem texture, leaves and economically useful organs. Use all three representations—words, formula and diagram—rather than expecting one to replace the others.
Solanaceae: the potato family
The Solanaceae family occurs widely across tropical, subtropical and temperate regions. Many members are herbs or shrubs and only some are small trees. Stems may be herbaceous and aerial, erect, cylindrical and branched, and may be hairy or hairless. An important variation is the underground stem of potato, which has stem identity because of its buds and nodes despite its subterranean location.
Solanaceous leaves are commonly alternate, simple and exstipulate, with reticulate venation. Rarely they can be pinnately compound, so 'always simple' would be inaccurate. The inflorescence may be solitary, axillary or cymose in different members. These vegetative clues narrow identification, but the combination of floral characters offers stronger family-level evidence.
The floral features that identify Solanaceae
A typical flower of the family is bisexual and actinomorphic. It commonly has five sepals united into a persistent calyx, with valvate aestivation. The corolla comprises five united petals, also generally described as valvate in this chapter. There are five stamens attached to the petals, so they are epipetalous. The gynoecium has two fused carpels, usually situated obliquely, and a superior ovary divided into two chambers. Numerous ovules attach to an axile placenta.
The familiar Solanaceae floral summary can be read as: actinomorphic, bisexual; K(5), C(5), A5, G(2), with a superior ovary and epipetalous stamens. It is a shorthand for typical characters, not a promise that every species has no variation. The fruit is often a berry or a capsule, and seeds are generally numerous and endospermic. A student given a flower showing five united petals, epipetalous stamens and a two-carpel superior ovary with axile placentation should consider this family while checking the rest of the plant.
| Character | Common Solanaceae description |
|---|---|
| Habit | Mostly herbs or shrubs |
| Leaves | Alternate, usually simple, exstipulate, reticulate |
| Flower | Bisexual and actinomorphic |
| Calyx / corolla | Five united sepals and five united petals |
| Androecium | Five epipetalous stamens |
| Gynoecium | Two fused carpels; superior, commonly bilocular ovary |
| Placentation | Axile; numerous ovules |
| Fruit / seed | Berry or capsule; many endospermic seeds |
Diversity and usefulness within one family
Tomato, brinjal and potato are familiar food plants belonging to this family, while chilli is commonly used as a spice. Members such as ashwagandha and belladonna have been used for medicinal compounds, although biological activity and toxicity vary and such plants must not be treated as safe remedies without appropriate expertise. Tobacco is another member, historically grown for fumigatory use. Petunia illustrates the family's ornamental value. These uses do not define the family; structural characters do.
How to study a flower specimen responsibly
Observe the intact flower first, then if appropriate open one flower carefully and count the sepals, petals and stamens. Examine how stamens meet the corolla, then make a lengthwise or crosswise view of the ovary to look for its chambers and placental attachment. Record what you actually see, marking any character that is uncertain. A useful written description is more valuable than a memorised label if it explains which observed features support the identification.
The phrase 'two fused carpels' is the feature that matters for the Solanaceae gynoecium. An ovary with two visible chambers is not by itself enough to identify a family, because several unrelated flowering plant families share that architecture.
Quick Quiz
Quiz
What is represented by K(5) in a floral formula?
Which feature is typical of Solanaceae?
What does G(2) signify?
Where are ovules usually attached in a typical Solanaceae ovary?
Which order is most suitable for scientific plant description?
Practice Problems
- Write a concise vegetative and floral description of a typical Solanaceae plant.
- Explain what the symbols K, C, A and G represent, and what parentheses mean.
- Why is a floral diagram useful even when a floral formula is available?
- List four useful Solanaceae plants and identify uses.
- Distinguish a family-defining structural feature from a practical use.
Model Answers
1. Mostly an herb or shrub; stem often erect, aerial and branched; leaves alternate, usually simple, exstipulate, reticulate; inflorescence solitary or cymose; flower bisexual and actinomorphic; five united sepals, five united petals, five epipetalous stamens; two fused carpels, superior bilocular ovary with axile placentation; fruit berry or capsule.
2. K is calyx, C is corolla, A is androecium, G is gynoecium. A number counts organs; parentheses indicate their fusion in one whorl, as in G(2) for two fused carpels.
3. A diagram shows spatial arrangement and relationships among the organs and the mother axis, details that may not be evident from a formula alone.
4. Tomato and brinjal are foods, potato is a food crop, chilli is a spice, petunia is an ornamental. Different examples can illustrate medicinal or other uses.
5. A family is recognised by a combination of inherited morphological characters such as united petals and epipetalous stamens. Human uses such as food, spice or ornament are secondary applications and do not establish taxonomic membership.
Key Takeaways
A scientific plant description follows habit → vegetative organs → inflorescence → floral whorls → fruits and seeds. K, C, A and G represent calyx, corolla, androecium and gynoecium; parentheses indicate fusion. Typical Solanaceae flowers are bisexual, radial, with five united sepals, five united petals and five epipetalous stamens. The gynoecium has two fused carpels, a superior usually bilocular ovary and axile placentation. Solanaceae includes tomato, brinjal, potato, chilli and petunia.