The Collaborative International Dictionary of English v.0.48:

Thallophyta \Thal*loph"y*ta\, n. pl. [NL. See Thallophyte.]
   (Bot.)
   A phylum of plants of very diverse habit and structure,
   including the algae, fungi, and lichens. The simpler forms,
   as many blue-green algae, yeasts, etc., are unicellular and
   reproduce vegetatively or by means of asexual spores; in the
   higher forms the plant body is a thallus, which may be
   filamentous or may consist of plates of cells; it is commonly
   undifferentiated into stem, leaves, and roots, and shows no
   distinct tissue systems; the fronds of many algae, however,
   are modified to serve many of the functions of the
   above-named organs. Both asexual and sexual reproduction,
   often of a complex type, occur in these forms. The
   Thallophyta exist almost exclusively as gametophytes, the
   sporophyte being absent or rudimentary. By those who do not
   separate the Myxophyta from the Tallophyta as a distinct
   phylum the latter is treated as the lowermost group in the
   vegetable kingdom.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Thallophyta
    n 1: used only in former classifications: comprising what is now
         considered a heterogeneous assemblage of flowerless and
         seedless organisms: algae; bacteria; fungi; lichens