it's possible that there's a technical scientific term for something, but people may often change the pronounciation and it becomes a 'folks' variant (in Russian such words are called разговорные слова, разговорная лексика, and also there are просторечные слова, просторечная лексика, просторечье and this connotation will be mentioned in the dictionary). In case with подсолнух word it's used on a massive scale due to 'language economy'.