An important factor in the popularity of Forsythia is that its flower buds are not damaged by hard frosts in March. Some research at Purdue University back in 1995 indicated that this was at least partly due to the fact that the flower tissues accumulate soluble sugars, that protect the cells from catastrophic effects of freezing.
It's quite often stated that Forsythia flowers contain the carbohydrate lactose, which is otherwise only found in milk secreted by the mammary glands of mammals. I'm not sure how this claim originated, but a study by biochemists at Tohoku University in Japan in 1991 failed to find any trace of lactose in the flowers.
Interestingly, in 1998 genetic engineers at the National Institute for Agrobiological Resources at Ibaraki in Japan managed to express mammalian milk proteins in tobacco plants, for potential pharmaceutical applications - a biochemical feat that half a billion years of plant evolution failed to achieve.