To solve this problem, we need to identify the flower that has a keel as a characteristic feature.$\newline$Let's analyze each option:$\newline \bullet$Tulip: Tulips belong to the family Liliaceae and do not have a keel. Their flowers are typically cup-shaped.$\newline \bullet$Indigofera: This genus belongs to the family Fabaceae (Leguminosae), which is known for having papilionaceous flowers.$\newline$ - Papilionaceous flowers have a distinct structure with three parts: the standard (or banner), wings, and keel.$\newline$ - The keel is formed by the fusion of two petals, which enclose the reproductive organs.$\newline \bullet$Aloe: Aloe belongs to the family Asphodelaceae and does not have a keel. Its flowers are tubular and not papilionaceous.$\newline \bullet$Tomato: Tomato belongs to the family Solanaceae and does not have a keel. Its flowers are typically star-shaped.$\newline$Based on this analysis, the flower with a keel as a characteristic feature is from the genus Indigofera.$\newline$Therefore, the correct option is Option 2: Indigofera.