Q.Describe the arrangement of floral members in relation to their insertion on thalamus.

Based on how the calyx, corolla and androecium are inserted on the thalamus in relation to the position of the ovary (gynoecium), flowers are of three types:

• Hypogynous flower: The gynoecium occupies the highest position on the thalamus, while the other floral parts (calyx, corolla, androecium) are inserted below it. The ovary is therefore said to be superior. Examples: mustard, china rose and brinjal.
• Perigynous flower: The gynoecium is situated in the centre and the other floral parts are borne on the rim of the thalamus at almost the same level (around the ovary). The ovary is said to be half-inferior. Examples: plum, rose and peach. …

The idea

On the basis of the position of the calyx, corolla and androecium in relation to the ovary (gynoecium) on the thalamus, flowers are described as hypogynous, perigynous or epigynous. The key point of comparison is which whorl sits highest on the thalamus and, correspondingly, whether the ovary is superior, half-inferior or inferior.

• Hypogynous flower:

  • The gynoecium occupies the highest position on the thalamus and the other parts — calyx, corolla and androecium — are situated below it (arising from below the ovary).
  • In this condition the ovary is said to be superior.
  • Examples: mustard, china rose and brinjal.

• Perigynous flower:

  • The gynoecium is present in the centre and the other parts of the flower are located on the rim of the thalamus almost at the same level as the ovary (the thalamus is somewhat cup-shaped and the calyx, corolla and androecium arise around the ovary).
  • Here the ovary is said to be half-inferior.
  • Examples: plum, rose and peach.

• Epigynous flower:

  • The margin of the thalamus grows upward, completely enclosing the ovary and becoming fused with it, so that the other floral parts (calyx, corolla, androecium) arise above the ovary.
  • In this condition the ovary is said to be inferior. …

Method: The "Which Whorl Sits Highest?" Ladder

Rather than memorizing three separate named conditions, rank the four floral whorls, calyx, corolla, androecium and gynoecium, by height on the thalamus, and read the classification directly off that ranking.

Picture the thalamus as a small hill, and imagine placing the four whorls on it at different heights depending on where they insert.

If the gynoecium sits on top, with calyx, corolla and androecium all inserted below it on the sides of the thalamus, the ovary is described as superior, and the flower is hypogynous (mustard, china rose, brinjal). A useful memory hook: "hypo" means below, and here the other parts sit below the ovary.

If all four whorls sit at roughly the same height in a ring, with the gynoecium in the centre and calyx, corolla and androecium arising from the rim of the thalamus at nearly the same level, imagine the thalamus cupped up around the ovary like a shallow bowl, the ovary is half-inferior, and the flower is perigynous (plum, rose, peach). …