Why does “百合” (ゆり, Yuri, Lilies) Signify Female Love in Japan?
In 1976, an article in a magazine for gay/homosexual readers, written by female readers was called “百合” (ゆり, Yuri, Lilies), and since then it signifies lesbians. Many novels or manga, porn spread this name and became more aware.
You have to be aware though that Yuri and lesbian are very different word. Lesbien (in Japanese, we shorten it to lezu) is more direct and sexual, and slightly disrespectful. On the other hand “Yuri” has a lighter, can mean more A-sexual love or a deep female friendship. In Anime, Yuri is a genre for female romance and friendship.
These images from “Arpeggio of Blue Steel” is a scene of female love between Hyuga and Iona. These Lilies are painted for above reasons.
This image from “Monster Story” is a scene of female love from Suruga to Hitagi. Moreover, she has various attributes besides Yuri.
This image from “citrus” is an extreme female love. In my opinion, this love has been beyond Yuri, so we call it “Gachi Yuri”. In your country, what do you call this love? Serious Yuri? Real Yuri?
By the way, in Japan, lilies have another meaning. You must not bring lily flowers to hospitals. If you need the detail, please confirm this article from “Angel Beats!”.