The Imperial lemon is thought to be a

lemon The lemon (''Citrus limon'') is a species of small evergreen trees in the flowering plant family Rutaceae, native to Asia, primarily Northeast India (Assam), Northern Myanmar or China. The tree's ellipsoidal yellow fruit is used for culin ...

and grapefruit hybrid. Its fruit is slightly larger than a lemon and has a more rounded shape.

References

{{DEFAULTSORT:Imperial Lemon Lemons Grapefruit Hybrid fruit