Crystal flowers are a strange and as-yet unexplained phenomenon related to Mania. Two forms of crystal flowers have appeared: red and blue. Fields of red or blue flowers are also a common appearance in dream sequences and hallucinations throughout the story, suggesting that they are integrally connected to the Deep Mania, but it is not clear whether these are the same as the crystal flowers that appear elsewhere.
Red Crystal Flowers
During the chaos of the Ten Days of Rustfire, the Underground Shepherd gave Julien a red crystal flower while they discussed the fate of the Corpseborne of BR-002. Julien crushed the flower and its pieces entered his body; this apparently somehow contributed to letting him bond with the Corpus and create a new Black Ring.
Blue Crystal Flowers
Blue crystal flowers are seen during the appearance of Dreya in the DisSea. Many broken crystal flowers surround the Realm Stele that commemorates those lost in Keylan's expedition, and the apparition of Dreya gives a blue crystal flower to the Chief to help them reach the ruins of the expedition's base camp. In the Eternal Nightmare, blue crystal flowers have restorative powers to one's sanity, similar to the Hypercube which they share a color with. Fields of blue crystal flowers are also seen around the rift in the Observatorium, and Shalom tells the Chief that the ones they hold dear "will inevitably reunite with you at the journey's end, amidst a celestial ocean of azure blossoms."