This may have been talked about already, but I'm going to take the risk...

I was just reading this old (February 2005) article from The New York Times, in which they mention a "lemonade tree", which is supposed to be a cross between a Meyer lemon and a New Zealand grapefruit.

Has anyone heard about this fruit?

They also talk about a orange eureka lemon.

This is the article...
http://www.nytimes.com/2005/02/02/dining/02lemo.html?pagewanted=1&_r=1

For a VERY interesting story, look up the life history of David Karp (The Fruit Detective), the author of the NY Times article you list above. An amazing life turn around. David is currently speaking at he CRFG meeting in California this week end. - Millet (889-)

Thanks, looking it up now...

The lemonade is very popular in New Zealand and Australia. I have one whose fruit are just starting to ripen. I have a relative with a big tree and he uses them for everything citrus. A mild sweetish flavour.

I have looked the lemonade tree up on google and found that indeed it is a variety specific to Australia and NZ. But the info I find on the net describes the lemonade tree as a cross between a lemon and a mandarin, which suggests that this would be a meyer lemon.
There also appears to be some confusion with the pink eureka lemon, which is also called "pink lemonade".

Now for that orange eureka lemon... anyone has info on that? Seems impossible to find on google, probably because of the too generic search terms...

I went and checked my lemonade tree. The fruit on it are slightly oval with no nipple. When ripe they are pale yellow.

The lemonade and myer lemon are distinct, I would say lemonade is a lemon/lime type hybrid, cant see a lot of mandarin in it but who knows ?
Here is a web page with both.
http://www.engalls.com.au/Citrus/Lemons/tabid/56/Default.aspx

Interesting! It would definitely make a nice addition to my collection. But it will be impossible to find here...

"Lemonade(Lemon x Grapefruit ): An odd hybrid that produces ‘lemons’ you can eat straight off the tree, sweet and juicy a good addition to the orchard. Also makes great lemonade."
From a NZ nursery catalogue I found. It also mentioned that the fruit was sold at a market in Wellington early 1980s.
The grapefruit would be the poormans orange (New Zealand Grapefruit) if it was pre1980s I presume. As for the lemon..meyer?..can't find anything.
Also found these sites
http://www.lyndale.co.nz/catalogue/plants.php?vcatid=1&vsubject=&vsearch=
http://www.plantetearth.co.nz/images/EdibleGardensCatalogue.pdf
From what I see on google it probably was a wild NZ hybrid between the above trees that was also eventually introduced/sold by Engells in Australia. And has never more than a backyard tree as far as commerce goes.
Then again I may be wrong...
I will have seeds when mine ripen in another few months if anyone is interested.
I don't know how true to type they will be.

Is this the Sanbokan lemon? Or the Sanbokan grapefruit? I have one which when I bought it was labeled Sanbokan grapefruit, but when I searched around on the internet it is also called Sanbokan lemon. I had one fruit on it last year and it was ok, nothing special.

The Sanbokan is pretty distinct, pear shaped with a fat neck and yellow skin.
Lemonades are more lemon like.