To most people a flower is petals. To a botanist the petals are nearly the least interesting part: they are the advertising, and the structure that identifies the plant is everything behind and inside them. A botanical illustrator has to see the flower the way the botanist does — as a set of whorls arranged around an axis, with a countable number of parts in each — and draw so that structure is visible. This guide lays out the anatomy, the vocabulary, and the conventions for showing it.

The Four Whorls

A typical flower is built of four concentric rings of parts on a swollen stem tip called the receptacle, from outside in:

1. Calyx — the sepals, usually green and leaf-like, enclosing the bud. Count them; note whether they are free or fused into a tube; note whether they persist under the fruit.
2. Corolla — the petals. Count them; note free or fused; note the shape of the tube and lobes if fused (funnel, bell, salver, two-lipped).
3. Androecium — the stamens, each a filament topped by an anther that holds the pollen. Count them; note whether they are attached to the petals or free; note whether they are all the same length (in mints and figworts, two are often longer); note how the anther opens and which way it faces.
4. Gynoecium — the pistil or pistils, each made of one or more carpels, with a receptive stigma on a style above an ovary that contains the ovules. Count the carpels (often visible as lobes on the stigma or chambers in a cut ovary); note whether there is one pistil or many.

When the sepals and petals look alike — as in tulips, lilies, and irises — they are called tepals, and the two whorls are the perianth. The iris is a good test: its three outer tepals (the falls) and three inner ones (the standards) are different shapes but are all perianth, and its stamens hide under petal-like style branches that fool most first-time illustrators.

Counting and the Big Division

Flower parts come in characteristic numbers. Monocots — lilies, irises, grasses, orchids — build flowers in threes. Most dicots build in fours or fives. Numbers above ten ("many") are common in the rose, buttercup, and cactus families. The count of each whorl is a diagnostic character and belongs in the drawing exactly. If your specimen has an unusual count, draw a typical flower or note the anomaly; do not average.

Ovary Position

One of the most important structural facts about a flower is where the ovary sits relative to the other whorls. A superior ovary sits above the point where sepals, petals, and stamens attach — it is the top of the flower's axis, visible inside the corolla (buttercup, tulip, pea). An inferior ovary sits below that attachment point, so the sepals and petals appear to grow from the top of it — the swelling under an apple blossom, a daffodil, or an evening primrose, whose long "stem" below the flower is actually the ovary. Half-inferior is intermediate. The position is visible in a side view and obvious in a longitudinal section, and it is a character illustrators should show deliberately, usually with a cut flower in the plate.

Symmetry

Actinomorphic (radially symmetrical) flowers can be divided into mirror halves along many planes — a buttercup, a wild rose, a columbine. Zygomorphic (bilaterally symmetrical) flowers have only one plane of symmetry — a snapdragon, a pea, an orchid, most mints, the penstemon. Zygomorphic flowers have a front and a back, and the drawing must choose an angle that shows the asymmetry: a pea flower drawn straight-on looks like nothing; drawn three-quarters, its banner, wings, and keel become legible. Radially symmetrical flowers are usually best shown once face-on and once from the side.

Fusion of Parts

Parts within a whorl may be free or fused: fused petals make a tube (sympetalous), fused sepals a cup, fused stamens a column or bundles. Parts of different whorls may also be fused: stamens attached to the corolla tube are epipetalous, which is why the anthers of a phlox or a primrose appear to sit inside the tube rather than on their own stalks. Fusion determines how the flower is built and how it falls apart when it fades, and it is the reason a "petal" cannot always be pulled off individually. Look for it before drawing; draw the tube as a tube and the lobes as lobes, not as five separate petals that happen to touch.

Sex of the Flower

Most flowers have both stamens and pistils (perfect or bisexual). Some plants carry separate male and female flowers on the same plant (monoecious — oaks, corn, most begonias) or on different plants (dioecious — willows, hollies, aspens). A plate of a dioecious species should ideally show both, labelled. A single flower from a monoecious plant should be labelled as male or female. This is a case where drawing what is in front of you, without the vocabulary, produces a plate that is incomplete without anyone noticing.

Inflorescences: How Flowers Are Arranged

Few plants carry single flowers; most carry an inflorescence, and its type is as diagnostic as the flower. The main types:

• Raceme — an unbranched axis with stalked flowers along it, oldest at the bottom, youngest at the top (lupine, foxglove, many mustards).
• Spike — like a raceme but the flowers are sessile, without stalks (plantain, many grasses at a glance).
• Panicle — a branched raceme, a raceme of racemes (lilac, oat, many grasses).
• Umbel — flower stalks radiating from a single point like umbrella ribs (onion, milkweed); a compound umbel has umbels on umbels (carrot, dill, cow parsley — the whole Apiaceae).
• Corymb — flower stalks of different lengths arising at different points but bringing the flowers to a flat top (yarrow, hawthorn).
• Cyme — a branched cluster in which the central or terminal flower opens first, then the ones below; the reverse order from a raceme. Common in the pink, borage, and stonecrop families. A coiled one-sided cyme (scorpioid) is the fiddlehead of forget-me-nots.
• Head or capitulum — many small, sessile flowers packed on a flat or domed receptacle and surrounded by bracts, so that the whole cluster looks like a single flower. The entire daisy family: sunflower, black-eyed Susan, dandelion. The "petals" are individual ray florets; the center is hundreds of disc florets.
• Catkin — a dense, usually pendulous spike of tiny unisexual flowers (willow, birch, aspen).

The order of flowering within the inflorescence — bottom-up in racemes, top-down in cymes — tells you which flowers to draw as buds and which as open, and it is a mistake to reverse it.

Bracts, Spurs, and Other Extras

Bracts are modified leaves associated with flowers — the green scales below a daisy head, the showy "petals" of a dogwood or poinsettia, the papery scales of a grass spikelet. They are easy to mistake for sepals. Spurs are hollow extensions of a petal or sepal holding nectar — the five long spurs of a columbine are its defining feature and the reason it must be drawn from the side. Nectaries, staminodes (sterile stamens, as in penstemon's bearded tongue), and coronas (the daffodil's trumpet) are all structures worth naming in your notes and showing in the drawing.

The Floral Dissection

A finished scientific plate usually includes at least one dissection: a flower cut in half lengthwise (a longitudinal section) showing the ovary position, the attachment of stamens, and the interior of the corolla tube; and often a single stamen, a single pistil, and a cross-section of the ovary showing the number of chambers. These are drawn at magnification with their own scale bar. Use a razor blade and a steady hand, cut through the center of the flower, and draw the cut face immediately — it wilts within minutes. Dissections are where the counting and the ovary position become undeniable, and they are the part of the plate most valued by the botanists who use it. The plate composition guide covers where they go.

A Working Checklist

For every flower: number of sepals, free or fused; number of petals, free or fused, shape of tube; number and arrangement of stamens, free or epipetalous; number of carpels, one or several pistils; ovary superior or inferior; symmetry radial or bilateral; inflorescence type and flowering order; bracts, spurs, or other structures. Fill it in before you draw, and check the drawing against it before you stop. The result is not a less beautiful drawing. It is a drawing of a particular plant, which is the whole point.