I forgot to post this link. Its academic tone might be a bit dense or boring (it's "The Medieval Garden Enclosed" from the Metropolitan Museum of Art) but the selected pictures of medieval works are jam-packed with images of flowers and the information given about the flowers shows their allegorical use well. Plus of course I get to include a picture with a cat at the expense of Professor Tolkien.
Such pictures suggest that Tolkien was not alone in his "floral fixation".
Plants in Medieval Art
And as another example of his use of flowers, we can look at the names he gives Hobbit lasses. Rosie Cotton of course. But there's also Pansy, Lily, Poppy, Peony, Myrtle, Belladonna, Pervinca, Salvia, Primula, Daisy, Marigold, Elanor--taken from the genealogies in LotR.