The Collaborative International Dictionary of English v.0.48:

Houseleek \House"leek`\, n. [House + leek.] (Bot.)
   A succulent plant of the genus Sempervivum (Sempervivum
   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.
   [1913 Webster]