This pollination table might help you. I don't know what you have, just what might be possible.

Japanese Heartnut (Juglans ailantifolia var. cordiformis)

Here is a link that might be useful: Heartnut Production

The "Lemon shape" is fairly common in my area and I doubt it's a juglans hybrid. The nuts don't show much if any such distortion

Johnny

Thanks for that chart jocelynpei.
I've recently read even experts don't know if Juglans cinerea and Juglans nigra can hybridize.

It's not Japanese Heartnut since it has a bumpy husk like black walnut, Japanese Heartnut has a smooth husk I believe. And the longer point is at the base, the longer side on this one is at the top.

That's interesting conifer50, because I've never seen any walnuts besides this one that has a lemon shape. Every single one I've seen over many years here have a perfect round shape besides this one.

Are you sure you weren't seeing immature walnuts, butternut trees, or Pecan trees? Because I think all normal walnuts have a lemon shape when immature and small in the spring/summer time.

This post was edited by treeguy123 on Sun, Sep 22, 13 at 16:11

Heartnut is smooth and slightly sticky on the husk. The husk can be slightly furry too, untill quite mature (Heartnut)

Here's mature ones with the "unorthodox shape"

Johnny

Thanks for that picture, there must be a certain smaller gene pool of this lemon shape Black walnut scattered or isolated about in some areas.

Agree w/conifer50 that it's just a variance of nut-shape & prb'ly not a hybrid.

Both appear to be just variations of BW.
I see BW run the gamut from round to 'lemon' to 'pear shape.
Some 'improved' BW cultivars, like Emma Kay , have nuts (after husk removal) that are quite football-shaped, pointy on both ends. Some of the really thin-shelled types, like Clermont, have very prominent 'shoulders'.