[Solution from source] In Australian Acacia the petiole becomes flat, green and leaf-like (a phyllode) and takes over photosynthesis. Opuntia has a phylloclade (flattened stem), Asparagus has cladodes, and Euphorbia has a fleshy stem. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.