I knew what the Sempervivum plant looked like:

Sempervivum × giuseppii (from Wikipedia)

But I’d never seen the flowers until a few days ago:

Sempervivum flowers (from Gardener’s Path)

They remind me of Clark Ashton Smith’s “The Demon of the Flower”:

Not as the plants and flowers of Earth, growing peacefully beneath a simple sun, were the blossoms of the planet Lophai. Coiling and uncoiling in double dawns; tossing tumultuously under vast suns of jade green and balas-ruby orange; swaying and weltering in rich twilights, in aurora-curtained nights, they resembled fields of rooted serpents that dance eternally to an other-worldly music. — “The Demon of the Flower”, Astounding Stories, Dec 1933