What's the difference between houseleek and sempervivum?

Houseleek

Definition:

• (n.) A succulent plant of the genus Sempervivum (S. tectorum), originally a native of subalpine Europe, but now found very generally on old walls and roofs. It is very tenacious of life under drought and heat; -- called also ayegreen.

Example Sentences:

Sempervivum

Definition:

• (n.) A genus of fleshy-leaved plants, of which the houseleek (Sempervivum tectorum) is the commonest species.

Example Sentences:

• (1) Mulch newly planted trees and shrubs after a good watering, and choose new plants adapted to drought, such as grey-foliaged plants, sages, lavenders, santolina, or those with fat leaves which store water, such as sedums and sempervivums.