thallophyta

 A phylum of plants of very diverse habit and structure, including the algæ, fungi, and lichens. The simpler forms, as many blue-green algæ, 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 algæ, 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.]