Each continent has indigenous species, and some also have species that have been introduced from other continents. The first are called "natives", the latter are referred to as "naturized", the common element between the both is they can grow unaided.
There are over 20,000 species of wildflowers growing in America belonging to more than 300 different families. The species are identified by their colour, the shape of the flower and it's geographic origin.
All flowering plants, including wildflowers, are called Angiosperms. These flowering plants appeared suddenly and miraculously 80-90 million years ago, and today they are the most abundant plant on earth.
During the Middle Ages, research was carried out that that identified over 6000 species of Angiosperms, some of them being wildflowers. From the 17th to 19th centuries there was a boom in botany research and more species of plants and flora were classified. One of the famous works was carried out by Charles Darwin who produced Origin of the Species however many other botanists also conducted research on American wildflowers.Today there is a strong interest in growing wildflowers, so much so that it is possible to buy them in packs of seed mixture.