Your fruit does not have the distinct 4- or 5-lobed pattern typical of the interior flesh of feijoas. The rind thickness is similar, your fruit is more seedy. I do not see evidence of the hard shell you first mentioned, unless it is very thin. If this is wild, native fruit, some person local to your farm will know the name. Try posting the images on the Name That Plant forum as mentioned above. You might have to rename the images to re-post them there, otherwise just provide links to these.

The first one looks like 'sweet william' before it gets flower buds. ? If its not a bother... I would let it grow to maturity and see if it flowers again.

Hi all, Thanks so much for all the feedback! In the meantime, I did find one other interesting resource: ENature.com. There are all sorts of ways of searching, including by zip code. It's not terribly convenient, once you have the results, but it's still interesting. I have another plant that I'd be curious to know the identity of, if anyone knows it. It's in the last two photos of this entry, with one closeup shot and one distant shot. I thought it was flowers when I first saw it, but up close, it almost looks like some sort of succulent (?). It was growing in the marshes beside the Delaware Bay - the structure visible in the background of the last shot is actually a ramp to a handicapped-accessible viewing platform to look out at the water (and it's a horseshoe crab sanctuary, so out on the spawning horseshoe crabs at the right time of year) less than 50 ft from the tide line.

Definitely not the Epipactis Helleborine. This particular plant stays in this form, and doesn't really sprawl when (if) it flowers. It seems to stay very compacted. If I recall, the flower was set in the leaves instead of forming out, if that makes any sense! I'll have to keep an eye on it every day to watch for a flower.