Floral Morphology: structure and shapes of flowers

Parts of a Flower

  • Pedicel - the stalk of an individual flower
  • Whorl - a cyclic group in a flower. The four whorls are the calyx, the corolla, the androecium, and the gynoecium.
  • Calyx - the sepals collectively.
  • Sepal - one member of the outermost whorl of a flower. Collectively, the sepals make up the calyx. The sepals may be free or fused.
  • Corolla-- the petals of the flower
  • Petal - one member of the second whorl of a flower. Collectively, the petals make up the corolla. The petals may be free (the flower then termed polypetalous) or fused into one piece (the flower then termed sympetalous).
    • Dicots usually have 4 or 5 petals or multiples of 4 or 5.
    • Monocot usually have 3 petals or multiples of 3 petals.
  • Perianth - the calyx and corolla together
  • Androecium - the male sporophyll within the flower, one of the four whorls.
  • Stamen - one member of the whorl of male sex parts. Each stamen consists of a filament and anther, where pollen is produced. Collectively, the stamens make up the androecium.
    • Tetradynamous - refers to four long and two short stamens in one flower
    • Monadelphous - refers to stamens united by the filaments into one column
    • Diadelphous - refers to stamens united by the filaments into two groups--often 1 in one group and 9 in another
  • Anther - structure containing pollen
  • Gynoecium - the innermost whorl, the portion referred to as the female sporophyll.
  • Carpel - one member of the whorl of female sex parts. Collectively, the carpels make up the gynoecium. Each carpel consists of an ovary connected to a stigma by a style. The stigma is receptive to pollen. Within the ovary, on the placentae (sing., placenta) are one or more ovules, which will mature into seeds. The open spaces inside the ovary are called locules or cells. The dividing walls are called septa.
    • A gynoecium of many separate carpels is termed apocarpous. The flower is said to have many simple pistils
    • A gynoecium of many fused carpels is termed syncarpous. The flower is said to have a compound pistil
    • A gynoecium with only one carpel is termed unicarpellate. The flower has a simple pistil.
  • Stigma - the sticky receptive surface for the pollen
  • Pistil term is also used. It refers to a single carpel if there is only one, or to the whole structure if the carpels are united.
  • Perfect flower - having both stamens and pistils
  • Complete flower - having sepals, petals, stamens, and pistils (all four whorls).
  • Monoecious - stamens and pistils on one plant
  • Dioecious - staminate and pistillate flowers on different plants (e.g. papaya)

Ovary Position

  • Superior -- the ovary is located above the calyx
  • Inferior -- the ovary is located below the calyx

    Be careful: the flower should be held so that the pedicel is pointing DOWN when determining whether the ovary is superior or inferior. Flowers hanging down from a plant are "upside down" and must be turned "upside up" to determine the ovary position.

Floral Symmetry

  • Actinomorphic--the flower has many axes of symmetry, e.g. no matter where you "cut it in half", the halves will match. Also called regular or radially symmetric
  • Zygomorphic--the flower has only one line of symmetry, e.g. there is only one way to divide it to get equal halves. Also called bilaterally symmetrical or irregular, though some texts reserve "irregular" for flowers with no axis of symmetry.

Corolla Shapes

  • Bilabiate - "two lipped" as in some members of fabaceae, zygomorphic
  • Campanulate - bell shaped
  • Funnelform - funnel shaped
  • Ligulate - the ray floret on a head
  • Papilionaceous -"butterfly" shape, zygomorphic
  • Rotate - flattened actinomorphic disk
  • Slaverform - tubular base flaired sharply at apice
  • Spurred - having a spur

Inflorescence Types

For each, the stalk of the inflorescence is called the peduncle and the stalk of an individual flower is the pedicel.

  • Solitary - just one flower on the peduncle
  • Spike - one unbranched axis and the flowers sessile (without pedicels)
  • Spadix - like a spike, but fleshy and the flowers usually reduced and unisexual. Often subtended by a bract called a spathe
  • Spikelet - like a spike, but with the flowers and inflorescence subtended by specialized bracts. Usually applied to the grass family (Poaceae)
  • Raceme - one unbranched axis and the flowers with pedicels
  • Corymb - like a raceme, but the pedicels all elongating to the same level to give the inflorescence a flat-topped appearance. The link shows a corymb-like arrangement of heads
  • Umbel - all the pedicels arise from one point at the top of the peduncle
  • Compound umbel - peduncles arise from one point and each in turn bears a smaller umbel. Common in the carrot family (Apiaceae)
  • Cyme - a central flower opens first and later flowers are borne on branches below it. Some cymes are one-sided. Some are scorpioid cymes, i.e. curled like a scorpion's tail.
  • Verticil or Whorl - the flowers are borne in a tight circle at each node
  • Panicle - the main axis has branches which are in turn rebranched
  • Head - many small flowers borne on a common receptacle; may look like a single flower. Common in the sunflower family (Asteraceae)