The seven flowers are the lotus, the lily, the sunflower, the opium poppy, the rose, the tulip, and the orchid. The subtitle of the book is "How They Shaped Our World." Sometimes these flowers did indeed influence world history, as with the Chinese opium wars, or the Dutch tulip mania. More often, the meanings attached to different flowers are a reflection of what society valued at the time. Potter's real emphasis in the book is that everything about these flowers is fascinating: their origins in various countries, how they were "discovered," the men who wrote books about them, their medicinal properties, their depictions in art, and literature. Sometimes her fascination with the minutiae of the different varieties and the pioneering flower breeders exceeded my own. There were some dry parts.
But there were lots of fascinating tidbits. Here are a few. When the Republicans were in the White House, they dug up all the roses in the White House Rose Garden that were named after Democrats. (It is unknown whether the Democrats did the same in return.) The Ottoman Sultan Ahmed III had luxurious tulip festivals which included tortoises wandering through the gardens with candles on their backs. The obsession with collecting orchids from the wild has driven many of them nearly to extinction, and one of the last Lady's slipper orchids in England was given an armed police guard to protect it from thieves.
My biggest complaint is that the book needed a lot more pictures. Every time she described a flower, or a work of art, I wanted to see that flower or work of art.