Roses, as some might say, are part of the inviolate triumvirate of stereotypical gifts men give women, along with chocolate and wine. Lotuses tend to be associated with narcotics and opium dens by some, likely due to the lotus being a popular motif in depictions of organized crime in early 19th century China. Chrysanthemums and peach blossoms once had cultural connotations and links to the Japanese and Chinese imperial thrones, respectively. Cherry blossoms, sakura to the Japanese, are treated as nature's subtle and beautiful way of reminding mortals of the short, evanescent nature of life as believed by Japanese who practice their Zen and Shinto religions. Flowers can have many meanings and many implications, varying from culture to culture, but there is one that (apparently) even science is not disputing: stress management.
Studies conducted by various organizations and groups in Japan and South Korea have found data that appears to indicate that growing flowers or simply viewing a flower garden is a viable form of stress management. This was quite observable during hanami, the three days of spring in Japan where most Japanese traditionally spend a day viewing the blooming cherry blossoms. According to studies, most of them showed remarkably lower levels of stress compared to those who did not. This effect has been associated in the past by other cultures and countries as well, as exemplified by the popularity of vast flower gardens in European palaces and estates. The study also showed that flowers, whether being viewed or received, had immediate effects on a person's mood, at times even alleviating the effects of depression and anxiety for a few minutes. Evidence also suggest that they make excellent ways to regulate someone's mood, which is considered a component of any attempt at stress management.
Common sense has long told people that being around flowers make people feel happy, or at least a little less dismal and drab. Now, science is starting to realize that common sense, in this case, was not entirely incorrect. There is currently no real data on how or why flowers are able to have such effects and if these effects are universal for all known flowers. However, there can be no disputing the fact that flowers being used for stress management and emotional therapy actually do work, even though how effective the tactic is varies from person to person. It is also unknown if the scent or the appearance of the flowers have any influence on the effect, though it is notable that no one wants to receive rotten flowers. There might also be links to memory-based reactions to the flowers, but this has not yet been fully explored.
There have also been some notes on how certain flowers seem to trigger specific emotions and areas of the brain. For example, roses seemed to stimulate areas of the brain that are known to react to intimacy and romance, which might explain why they're such popular choices for dating. The aforementioned cherry blossoms and peach blossoms both appeared to have a soothing effect, relieving tension, particularly in large amounts. Gardenias, hydrangeas, and other small flowers were notable because they gave test subjects a sensation of tranquility and calm, stimulating areas similar to those touched upon by cherry and peach blossoms. The study noted other effects caused by other flowers, but noted that they were similar to the ones noted above.