Plant Ecology of the Sonoran Desert Region - Design with the Desert: Conservation and Sustainable Development - page 151

Carpel (pistil)

Stigma

Style

Anther

Stamen

Ovary

Filament

Corolla Petals

Perianth

Ovule

Calyx -Sepals

Pedicel

Receptacle

FIGURE 8.1
Generalized diagram showing the major parts of an angiosperm flower.

are sufficient to eliminate every other possibility in the world and leave the correct answer
standing. Assume, for example, that the unknown thing is a dog. First question: “Is it
a concept?” (No—therefore it's an object.) Second question: “Is it alive?” (Yes.) Third
question: “Is it a plant?” (No.) Fourth question: “Is it a vertebrate? (Yes.) Fifth question: “Is
it an herbivore?” (No.) The enormous inventory of the universe has been narrowed to a
very short list in only five questions.
Botanists identify plants (and zoologists animals) unknown to them, with a Twenty
Questions-like procedure called a dichotomous key (or simply key). A key is a nested series
of dual choices that quickly narrows the possibilities to a single species. For example, the
first pair of choices might ask you whether the flower has three petals versus four or five.
Each of the two possible answers leads to another pair of choices, and so on until you have
identified your quarry out of 300,000 species of flowering plants. But before you can use
such a key effectively, or before you can describe your unknown to someone who will
identify it for you, you must know the parts of the flower and plant you are examining.
The sepals collectively make up the calyx . They enclose all other flower parts in the bud,
usually completely concealing the rest of the flower until it opens.
The petals collectively make up the corolla . Petals are frequently the visual advertising
banner that attracts pollinators. Petals and sepals look similar in many flowers, such as in
lilies and agaves. By definition the sepals are the parts on the outside; petals are typically
concealed in the bud.
The corolla and calyx make up the perianth . The perianth parts may be separate or fused
together for part or all of their length. Often there is only one series of perianth parts. Of
necessity these must be on the outside and therefore they are sepals, even if they are large
and colorful.
The female part of a flower is the pistil , composed of stigma, style, and ovary. The ovary
contains ovules, which develop into seeds when fertilized by the sperm in pollen. Seeds
are plant embryos encased in a protective membrane and usually contain stored energy
to fuel germination. If the ovary is visible beneath the calyx, it is said to be inferior. It is
superior if you must look inside the flower to see it (i.e., it is above the calyx).
The male part of a flower is the stamen , composed of the anther and the filament. Anthers
produce pollen grains, which contain sperm cells.