The largest orchid leaf belongs to Elephant Ear Orchid (species name: Phalaenopsis gigantea). The photos below are taken in Sabah Agriculture Park (Taman Pertanian Sabah) in Tenom.
The leaves of Elephant Ear Orchid are so huge that no wonder it gets its name. I know there are a few lowland forest in Sabah where you can see this orchid but I haven’t seen one in the wild so far. In the Botanical Garden of Tawau Hills Park, there was one cultivation that has leaf measured 60.5 x 22.5 CM.
Based on my understanding, flower usually spends the most resources on fruiting, so it makes me wonder that why this orchid wants to develop huge & thick leaves, so big that it’s inflorescences are hidden behind the leaf.
Photos taken in Tenom, Sabah, Malaysia Borneo