In Boca-Joe's above post showing all the various leaf forms, tri, mono, rounded, broad and slim, are these seedlings that are shown coming from seeds that came from a single fruit? - Millet

Like Joe said, there is a lot of variation with the seedlings from this variety of Citrandarin.

I have read that Citrandarin US-852 is highly zygotic. As much as 50% of the seedlings will not be true-to-type.

This is one, of many, reasons why this Citrandarin was discontinued as a rootstock in Florida. It was recommended that it be propagated chiefly by tissue culture instead.

You might be interested in reading this document about it:
PDF on US-852 Citrandarin

Thanks Klemmd, I will read it. Appreciate the link. - Millet

What's interesting is when I talked to someone in Florida at the USDA who sent me this link about US-852, and I mentioned how unexpectedly 'un-trifoliate' this fruit tasted -- and that it might have 'potential' in the North, he said that likely no one down there had ever even tasted the fruit!

Just makes you wonder with all the money being spent on disease-resistant rootstocks -- if some of that money and research was diverted to developing truly cold-hardy edible citrus, it could probably be done!

Of course no one in Florida would care -- and they certainly would not WANT to develop ANYTHING that would compete with Florida's $9 billion citrus industry.

That is what I were always thinking. They do not really try to develop frosthardy citrus plants. And the army of lay people and hobbists is discouraged and thinks: If they cannot create a tasty frost hardy citrus who am I to try that? But how can that be that the only relatively tasty and hardy citrus plants were created by a few European hobbists with no money and little land? And how can that be that we have almost no third generation hybrids and still cultivate Rusk citrange and Morton that were bread up to 100 years ago? They have given up the task in Florida long ago, I think. And I do not wonder since the standards for commercial citrus plants is so high that no possible hybrid of the next 200 years will be able to compete with the current varieties on the market. Let them taste perfekt if they are seedy they will not be sold... And so on.
But its a pity that they don't try breeding such plant. What would I give for the thousands of zygotic seedlings that they throw away each year when they sell their rootstocks?!

If I see trifoliate leaves, I avoid it like the plague.

As far as tasting goes that is...

Oh so harsh! Well, if I had winters milder than -15°C (5°F) with no risk of -20°C (-4°F) than perhaps I would be tempted to do the same.

We'll just pull all the extra leaflets off before we have you taste test our new future hybrids Laaz

Till,

If we were in the same financial state now as we were back in the 1970s or 80s likely someone at the US Arboretum could have been working on it....a horticulturist -- not a Florida Citrus interest.

At the arboretum they have done a lot of breeding over the years to develop hardy ornamentals such as hardy crape myrtles, camellias and so forth. Why not citrus?

Unfortunately a lot of research $$ have dried up. The US Arboretum is hurting from lack of funding right now.

Till, promoting a hardy citrus that was "relatively tasty" (kind of tasty) would be a huge looser financially, even if all the hobbyist purchased one. Researchers would never waste their time trying to find a "relatively tasty" citrus fruit. - Millet

Oh, I completely understand that. It would financially not be worth it. But still it is a pitty for us hobbists. We are glad for every hybrid that let us hope for better hybrids. But they throw them away untested. Very much understandable but a pitty!

ilyaC yes, the decorative market exist, but that limited market would never attract research. The people and organizations that have the talent and the financial ability in citrus research are not interested, and will never be interested. There is little benefit in it, and no real money in it. - Millet