Dionaea - trap construction
The leaf consists of a broad flat petiole serving photosynthesis and a two-lobed leaf lamina, which during growth is folded around the midrib perpendicular to the petiole. At low light intensity the summer leaves do not develop. A row of teeth is located along the edges of the lobes. The teeth grow into the closed cavity of the leaf lobes until the leaf is mature and the lobes opens, and then the teeth straighten out. Star-shaped glandular hairs on the abaxial side of the leaf and along the teeth on the adaxial side secrete carbohydrates and are assumed to lure prey to settle on the lobes, but experiments show a small effect. The border zone along the teeth absorbs ultraviolet radiation and like the petiole and other green leaves appears dark seen with the UV-sensitive eyes of insects, while the central part of the leaf lobes appears light, and the area constitutes a conspicuous resting place. The adaxial sides UV-reflecting part is closely covered with digestive glands which contain the red stain anthocyanin in the vacuoles of the glands and the more, the more brightly the plant is illuminated.
H. S. Heide-Jørgensen, november 2020.