Medicinal Flowers: Definition and Structure

• Lecture Subject: Medicinal Flowers
• Lecturer: Dr. Dalia El-Sheikh Ali, Lecturer of Phytochemistry and Pharmacognosy

Learning Outcomes

• Understand the definition of a flower and its importance.
• Learn the structure of a typical flower.
• Identify the components of a typical flower.

Definition of a Flower

• A flower is a compressed, modified fertile shoot with modified leaves.
• Flowers facilitate the production of fruit and seed for plant propagation, and in particular a new generation.
• Flowers are important for plant identification.

Function of Flowers

• The primary biological function of a flower is to produce male and female gametes.
• Flower facilitate the production of seeds after fertilization.

Structure of a Typical Flower

• A flower sits on top of the stem, which is called a pedicel.
• At the top of the pedicel is a swollen tip called a receptacle.
• Sepals, petals, stamens, and carpels are borne on the receptacle.

The Floral Parts: Essential vs. Non-Essential

• Non-essential parts include the calyx (sepals) and corolla (petals).
• Essential parts include the androecium (stamens) and gynoecium (carpels).

Components of a Typical Flower

Sepals

• Sepals are the first whorl on the receptacle.
• They are frequently green.
• Together, sepals are known as the calyx.
• The sepals protect the flower bud before it opens.

Petals

• Petals are brightly colored modified leaves and have a velvety touch.
• Together, petals are known as the corolla.
• When the calyx and corolla are similar, they are referred to as perianth.
• Sepaloid refers to the green calyx.
• Petaloid refers to the colored petals.
• The functions of petals include attracting pollinators and protecting the reproductive organs.

Stamens

• Stamens are the male reproductive organs of the flower.
• A collection of stamens are known as the Androecium.

Structure of a Stamen

• The anther is divided into two anther lobes by connective tissue.
• Each anther lobe possesses two pollen sacs containing numerous pollen grains.

Carpels

• Carpels are the female reproductive organs of the flower.
• A collection of carpels is collectively known as the Gynoecium.

Structure of a Carpel

• Each carpel consists of a:
  • Stigma
  • Style
  • Ovary

Additional Components

The Bract

• A bract is a leafy structure from the axil of which the flower arises.
• Flowers with bracts are described as bracteate.

Involucre

• An Involucre is group of bracts arranged in one or more whorls.
• Involucre structures surround a group of flowers as found flowers such as in Umbelliferae and Compositae flowers .

Flower Types

• Flowers can be bracteate (possessing a bract) or ebracteate (lacking a bract.)
• Flowers can be solitary or part of an inflorescence.

Inflorescence

• An inflorescence is a group of flowers arranged in a particular way on a stem.
• The stem holding the whole inflorescence is called a peduncle.
• The main axis of the inflorescence is termed the rachis
  • Also referred to as pedicel in flowers.

Flower Presentations

• Flowers can be pedicellate (having a pedicel) or sessile (lacking a pedicel).

Flower Classification

According to Presence of All Parts

• Complete flowers contain sepals, petals, stamens, and carpels.
• Incomplete flowers lack one or more of these parts.

According to Symmetry

• Actinomorphic (Regular): Flower is symmetrical in all directions.
• Zygomorphic: Flower is symmetrical in one direction only.
• Asymmetric: Flower is not symmetric in any direction.

According to Number of Segments in Each Whorl

• Trimerous: Flower segments in multiples of three.
• Tetramerous: Flower segments in multiples of four.
• Pentamerous: Flower segments in multiples of five.

According to Number of Whorls

• Pentacyclic: Flower shows 5 whorls.
• Tetracyclic: Flower shows 4 whorls.

According to Arrangement of Parts

• Cyclic: Floral leaves are arranged in definite circles or whorls.
• Acyclic: Floral leaves are arranged in a spiral manner.

According to Presence or Absence of Androecium and/or Gynoecium

• Hermaphrodite (Perfect): Both male and female organs are present.
• Unisexual: Only one of the reproductive organs is present
  • These may be staminate or pistillate.
• Sterile: Both male and female organs are absent.

According to Number of Stamens

• Monoandrous: One stamen.
• Diandrous: Two stamens.
• Triandrous: Three stamens.
• Tetrandrous: Four stamens.
• Pentandrous: Five stamens.
• Polyandrous: Many stamens.

According to Sepal and Petal Fusion

Petals

• Apetalous: No petals.
• Gamopetalous (sympetalous): Petals are united.
• Polypetalous: Petals are not united.

Sepals

• Gamosepalous : Sepals are united.
• Polysepalous: Sepals are not united.

Structure of the Flowers

Calyx

• Calyx may be:
  • Foliaceous (leafy), e.g., Stramonium
  • Very small
  • Membranous, e.g., Pyrethrum
  • Bristles, e.g., Arnica

Corolla

• Insertion of the Corolla
• Hypogynous: Corolla attaches to the receptacle below the ovary; the ovary is superior.
• Perigynous: Corolla is inserted on the edge of the hollow receptacle which does not fuse with the ovary; the ovary is semi-inferior or half inferior.
• Epigynous: Corolla attaches to the receptacle above the ovary, the receptacle fuses with the ovary; the ovary is inferior.

Reproductive Organs: Androecium (Stamens)

• Presence of pollen grains:
  • No pollen grains = sterile (Staminode).
• Presence of filament:
• Filament may be absent (anther is sessile).
• Types of androecium according to length of stamens:
• Didynamous: Formed of 2 long & 2 short stamens.
• Tetradynamous: Formed of 4 long & 2 short stamens.

Detailed Stamen Structure

• Stamens include Petal, Stigma, Anther, Filament Style, Stamen, Microsporangium, Microspores, Tepetum, Carpel and Sepal

Cohesion of Stamens

• Stamens can be free or united.
  • Fusion through anthers is known as Syngenesious, e.g., Compositae.
  • Fusion through filaments can be:
    • Monadelphous (leguminosae)
    • Diadelphous
    • Polyadelphous (clove...tetradelphous).
• Stamens
• In Monadelphous stamens all the stamens are united in a tube through the filaments.
• In Diadelphous stamens the stamens are arranged in two groups, each is united by the filaments
• In Polyadelphous stamens the stamens are united by the filaments in three or more groups

Pollen Grains

• Pollen grains consist of a wall of two membranes:
• Exine: Outer thick cutinized wall.
• Intine: Inner delicate cellusic membrane.
• Fine exine may be smooth, warty, pitted, or spiny.
• Pollen grains contain germ pores and germ furrows.

Gynaecium Classification

• Consists of one or more carpels
  • Each gynoecium consists of Stigma, Style and Ovule/Ovary

Classification according to Number of Carpels

• One carpel= monocarpellary.
• Two carpels = bicarpellary.
• Many carpels (>2) = multicarpellary.

Classification according to Fusion of Carpels

• Carpels can be either Free or United
  • Apocarpous- Is free
  • Syncarpous - Is United
• Fused carpels are more common, with fusion occurring at their margins.
• At the base of the carpel is the ovary.
• Simple ovary comes from monocarpellary gynoecium.
  • Compound ovaries come from bi- or multicarpellary gynoecium.
• When margins of carpels fuse, they form the placenta, to which ovules attach.

Style

The style is part of the carpel structure between the stigma and the ovary. It may be:

• Very long or very short.
• Absent.
• Flattened.

Stigma

• Stigma can be stalked or sessile (when the style is absent).
• Stigmas are usually colored and sticky.
• They're usually covered with papillae to receive pollen grains.

Stigma - Forms

• Different forms include:
  • Capitate
  • Globose
  • Tubular
  • Lobed
  • Stellate
• Stigmas may also be papillosed.
• Receptacle: Usually flattened, convex, or conical.
• May be elongated below the calyx (hypanthium).