Hi there,
I found a Citrus in a village garden in Western Province of Papua New Guinea.
It had no fruits, so I couldn't identify it by the fruit.
But I did notice a peculiar character with the plant, it has no marked petiole, ie. no petiole wings, and no "joint" between leaf blade and petiole. The short petiole simply becomes leaf blade without any "joining line/mark" like you see in most other Citrus.
They say the fruit is a bit sour like lime or lemon, and the tree we saw is short, 2-3 metres tall and thorny. This was growing in the muddy swamp in the hot lowlands.
Any idea what it could be? The villagers said it was planted from somewhere else.