What is it for citrus?

[pher]

What is it for citrus?
Probably ponderosa.They said that it is a hybrid of lemon and grapefruit.

[brian]

I'm not very good at identifying these but it does look very much like a ponderosa lemon I once owned.  They are really cool trees, the fruit is huge. 

[Chas]

C. lemon 'Lipo' is also a hybrid of lemon and grapefruit! It is absolutely the same as Ponderosa just the fruit rind is a good indicator! 

[Chas]

Sorry, to be more precise:
C. Lemon 'Lipo'(Imperial Lemon) is belived to be C. Limon x C. paradisi.
C. lemon Ponderosa is believed to be Citrus limon × medica.
Both plants are similar regarding leaves, grow habit, blossoms just the fruit taste is different, Lipo has poor lemon aroma. 
I've also C. Lemon nine pounder(no fruit yet) which is very similar with Ponderosa and Imperial Lemon just has few nice thorns.