Are "ピーナッツ" and "ピーナツ" both correct for "peanut(s)"?


I've just noticed that the usual word for "peanut" or "peanuts" in Japanese is
"ピーナッツ" (pīnattsu), but the first spelling I found, from looking in the
translation table in the English Wiktionary was actually "ピーナツ" (pīnatsu).

It turns out the first one has its own entry while the second one is just a
redlink in the English entry's translation table. But both seem to get plenty
of Google hits.

Are they both correct? Might they have slightly different usages, such as in
combining forms or singular vs plural?

Since I'm asking, there is also 落花生{らっかせい}. Is it no longer used in favour of
the English-derived term?




Searching the [_Balanced Corpus of Contemporary Written Japanese
(BCCWJ)_](http://www.kotonoha.gr.jp/shonagon/) gives the following results:

[code]

    ピーナツ　　　１１６件
    ピーナッツ　　１８８件
    
[/code]

So it seems like the latter is somewhat more common. All of these results are
drawn from contemporary sources, and although ピーナッツ is more common, ピーナツ is
common enough that I think, descriptively speaking, both spellings should be
considered correct.

Looking through the corpus results, I don't see any obvious patterns in usage.
Both spellings seem to be used interchangeably. I don't see any reason to
consider them separate words.

Out of curiosity, I decided to search for ドーナ(ッ)ツ:

[code]

    ドーナツ　　　２３２件
    ドーナッツ　　９３件
    
[/code]

It's interesting that here, the trend is toward the shorter spelling. But
again, I don't see any obvious patterns in usage to suggest that they should
be considered separate words.

So in short, the most common spellings for the two words appear to be ピーナッツ
and ドーナツ, but the other spellings seem to be common enough that I'd say
they're variants rather than misspellings.

