Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Core eudicots
Order: Saxifragales
Family: Crassulaceae
Genus: Hylotelephium (was in the genus Sedum)
Species: H. telephium
Sub Species: H. telephium ssp. maximum
Cultivar name: Hylotelephium telephium 'Purple Emperor'
Common name: Sedum 'Purple Emperor', Sedum 'Washfield Ruby'

This cultivar Hylotelephium telephium 'Purple Emperor' is a succulent perennial whose original parents are native to Eurasia. Hylotelephium telephium subsp. maximum 'Atropurpureum' was one parent, although the other is still a mystery. Its common name 'Purple Emperor' was named after a rare Eurasian butterfly Apatura iris. This cultivar was first spotted as a seedling by Graham Gough, of Marchants Hardy Plants, growing in his parents' garden in East Sussex.
It is a fast-growing, compact, deciduous, herbaceous perennial which grows >50cm tall and has broad, plum-black leaves which are whorled in threes at the top of each erect dark red stem. Rounded clusters of small, pale purplish-pink flowers develop in late summer. These heads of tiny flowers are very attractive to bees, butterflies and hoverflies.

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Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/