Eschscholzia californica has naturalized in my country and a lot of people think they belong to our native flora. We love them, because of their beauty and, although abundant, they have not become invasive.
The story tells that when our railroads were built, there was a young US engineer/supervisor that wrote to his mom in the USA that he was homesick and that in order to stay until his assignment was finished, he needed something to remind him home. His brilliant mother sent him a big bag California Poppy seeds that he scattered all along our railroads