Flower company - the flower growers are not part of the flower seller's company.
If the slower growers contract with the flower seller to sell their flowers, they are still not part of the flower seller's company but they may have contractual rights about the selling of their flowers - anything from advertising, priority, amount, price, etc.
Race Car LLC or similar named companies - it'll all be up to the individual state where they "license" (or whatever terminology is used in that state) their name or with the Federal government if there are copyright or other legal provisions for the name.
Obviously if someone does not "license" the name or properly go through legal channels, then the wronged party can go to the government entity that regulates the names and file a complaint or go through the court process to enjoin them from using the name. There are no clear cut answers to the second question you ask on race cars.
The above opinions are just personal opinions and not legal opinions, Contact your attorney or legal counsel to determine your individual legal rights.