No such thing as a national flower for France. And if there was one it wouldn't be the iris anyway. And many other countries don't have that concept either.
This is some bullshit made up by an American florist trying to sell flowers to people who identify as 1/67th Slovenian.
England doesn't really have a national flower. The Tudor Rose is a heraldic creation to symbolise the fusion of the House of York and House of Lancaster after the wars of the roses, and the formation of the House of Tudor.
The two houses used white and red roses as symbols, and the Tudor rose was created as a mixed red and white rose which does not exist.
A real rose for England is otherwise a loose thing, not an official symbol.
And they've highlighted the whole of the UK for "England". Scotland has the thistle, Wales has the daffodil and Wikipedia says that flax is widely used as a symbol of Northern Ireland.
As many here have commented, the map is pretty bad and lots of these are not officially recognized as national flowers.
Having said that, actual national flowers, much like national animals, are often just whatever commonly grows in the country (assuming there is one flower that really sticks out).
They don't have to be unique, because you'll have a flag or a coat of arms for that purpose (which may portray that flower or animal, for what it's worth). So, they're rather just part of the "national branding", if you will.