The Collaborative International Dictionary of English v.0.48:

midsummer-men \midsummer-men\ n. (Bot.)
   A Eurasian mountain plant (Sedum rosea) with fleshy
   pink-tipped leaves and a cluster of yellow flowers.

   Syn: rose-root, Sedum rosea.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Sedum rosea
    n 1: Eurasian mountain plant with fleshy pink-tipped leaves and
         a cluster of yellow flowers [syn: rose-root, midsummer-
         men, Sedum rosea]