Keel is the characteristics feature of flower of

The correct option is Indigofera.

In botany, a keel (or carina) is a characteristic feature of flowers belonging to the family Fabaceae (also known as the pea family or Papilionaceae).
The petals in a papilionaceous corolla (typical of the pea family) are arranged in a specific butterfly-like pattern consisting of five petals:
1. Standard (Vexillum): The largest, outermost posterior petal.
2. Wings (Alae): Two lateral petals positioned on either side.
3. Keel (Carina): The two innermost anterior petals that are fused together to form a boat-shaped structure. This keel encloses and protects the reproductive organs (stamens and carpel) of the flower.

Let's evaluate the given options based on their plant families:
• Indigofera: This genus belongs to the family Fabaceae, which is characterized by the presence of a papilionaceous corolla containing a keel.
• Tomato: Belongs to the family Solanaceae, which features actinomorphic flowers with united petals (gamopetalous) forming a wheel-shaped (rotate) corolla.
• Aloe: Belongs to the family Asphodelaceae, characterized by tubular flowers with six perianth segments (tepals) instead of distinct sepals and petals.
• Tulip: Belongs to the family Liliaceae, which has regular flowers with six tepals arranged in two whorls of three.

Therefore, the keel is the characteristic feature of the flower of Indigofera.