Flower stems do more than hold flowers aloft. Each flower's stem is one branch of a plant's transport system, through which the flower receives water and minerals absorbed by the roots. It's an important job if there's to be a next generation--flowers are the reproductive organs of flowering plants.
The peduncle is what you might call the stem proper--the stalk of the flower, or what you hold when you want to give the flower to a beloved. If it's green, besides transporting minerals and water, it is helping to create food through photosynthesis.
Sometimes there is one peduncle per flower. Other times, though, the peduncle stalk branches into "mini-stalks," each holding its own flower. These clusters of flowers, usually produced by plants that rely on wind for pollination, are called inflorescences, and the stemlets holding the inflorescences are called pedicels, or pedicles. Big showy flowers like tulips don't have need of pedicles and rest on single peduncles.
At the end of the stem, rising up beneath the flower, the stalk swells. This swelling is called the receptacle. All the flower parts are attached here, so the receptacle serves as a sort of pedestal for the flower. The arrangement of parts is not as simple as first comes the peduncle, then the receptacle, then the flower, however. The relationship of the female parts of a flower with the receptacle is not always the same.
The female part of a flower is its ovary. Sometimes it sits above the receptacle, as in the case of buttercups. This situation makes the flower a hypogynous flower, and the ovary, sitting above the receptacle, is said to be superior.
When the ovary is superior, but is cupped by the receptacle, the flower is called a perigynous flower. The other parts of the flower--sepals, petals and stamens--are arranged on the rim of the receptacle. Roses and cherry blossoms have perigynous flowers.
A final type of flower as determined by the receptacle is called an epigynous flower. These flowers, which include the honeysuckle, iris and aster, have inferior instead of superior ovaries--that is, the receptacle encloses the ovary and the other flower parts are attached above.
Thorns and Spines
Not all flower stems possess thorns or spines, though for stems that have them, they're not easy to miss, especially by touch. Rose stems are famous for having thorns, there to protect the plant from herbivores. Cacti have spines. Thorns and spines are not always just a type of stem growth; sometimes they're modified stems or leaves.