The Collaborative International Dictionary of English v.0.48:

Althaea \Al*th[ae]"a\, Althea \Al*the"a\, n. [althaea, Gr. ?.]
   (Bot.)
   (a) A genus of plants of the Mallow family. It includes the
       officinal marsh mallow, and the garden hollyhocks.
   (b) An ornamental shrub (Hibiscus Syriacus) of the Mallow
       family.
       [1913 Webster]

WordNet (r) 3.0 (2006):

althea
    n 1: any of various plants of the genus Althaea; similar to but
         having smaller flowers than genus Alcea [syn: althea,
         althaea, hollyhock]