Sepals

• Modified leaves used for protecting the delicate structures on the flower while in bud stage

• Some sepals appear quite petal-like, and if it is difficult to distinguish, the term tepals is used

• Sepals are sometimes leaf-like structures

• Collectively sepals are known as calyx

Petals

• Modified leaves that are showy structures to attract pollinators 

• Absent in wind- and water-pollinated flowers (see catkins)

• Collectively known as corolla

• Perianth: The term "perianth" refers to both the corolla and calyx

  • Tepal: If the sepals and petals look identical, the term "tepal" is used.

  • Nectaries: organ with sugar-rich liquid called nectar, usually found at the base of the perianth for animal pollinators

Stamens

• Also known as the androecium

• Pollen-producing or male portion of the flower

• Most stamens have two parts: anther and filament

Anther

• Pollen-producing structures

  • Pollen is the dispersed microspores of a seed plant that contain the male gametophyte of the plant

• Site of meiosis to create pollen (or microspores)

• Most angiosperm anthers are four (4) fused microsporangia

• Tapetum: a layer of cells inside of microsporangia that provides nutrition to developing pollen

Filament

• Stalk which elevates anther to dust pollinators

• Over evolutionary time, anther-bearing leaves reduced into the filament of derived angiosperms

• Some ancient angiosperms (e.g. Austrobaileya, Degeneria) still have leaf-like or petal-like stamens

Pistil

• The female portion of the flower; also called the gynoecium

• The pistil usually has three parts: stigma, style, and ovary (see below)

• The term "carpel" refers to a single-seeded structure; it is the ancestral state.

  • Some ancestral angiosperms exhibit carpels, not pistils (e.g. Magnolia - see image below)

  • A pistil is the evolutionary result of the fusion of several carpels

• Developmentally, pistils/carpels are modified leaves that completely envelope the seeds

  • Over evolutionary time, ovule-bearing leaves folded lengthwise to form the carpel

  • This is thought to be an adaptation to protect the ovules

  • Some ancient angiosperms (e.g. Akebia, Degeneria) have carpels that do not completely close during development, called conduplicate carpels (see image below)

Stigma

• A landing pad for pollen; the site of pollination 

Style

• A stalk that elevates the stigma to the height of the anthers

Ovary

• The ovary protects ovules and develops into the fruit 

• Ovules are unfertilized seeds

• Ovules are called "seeds" after fertilization