Amboin aka Citrus amboinensis.
Apparently this species was collected in Papua New Guinea, and is allied to limes and hystrix. The fruit in pic1 are about 3.5 cm, which is big for this spp.
Later they turn a dull yellow/gold type of colour.
Fruit is fairly close to KaffirLime C.hystrix in flavor (acrid ?), perhaps the peel not as pleasently scented.
pic2 shows a seedling scion budded to rootstock after 18 months.
I think it gives a fair indication of what the plants look like at various growth stages.