As of 19 May 2014, both Index Fungorum and MycoBank state that Sparassis crispa is the current name.
Petersen, Ron and Hughes, Karen (2014) Cauliflower Tales, McIlvainea 23 (13-15): http://www.namyco.org/..., advocates splitting Sparassis crispa into S. crispa, S. americana, S. americana f. arizonica, and S. radicata, even though some interbreeding is possible, at least in the lab.
This species is distinguished by a central trunk from which all the folliations (flabellae) arise. The flabellae are azonate.
Light & Woehrel separated Sparassis radicata from S. crispa on the bases of DNA sequence analyses, reproductive and morphological criteria, yet they give no evidence of any of these. The microcharacters seems identical in their article, the macrocharacter in their key that separates them is a branched stalk for S. crispa and an unbranched stalk for S. radicata. No photos were provided of this feature. Sadly, no indication was given on the number of gene segments analysed. In the 1970’s Gilbertson found that the hyphae from European S. crispa and the Western US S. radicata could combine and synonymized them. Literature cited indicates three loci analysis is the bases of the DNA evidence, but no data is given (3%?). This article fails to give a solid reason to separate them at this time.
Light, William and Mary Woehrel. 2010. Clarification of the Nomenclatural Confusion of the Genus Sparassis [Polyporales: Sparassidaceae] in North America. Fungi 2 (4): 10-15.
See the Winter 2009 edition of Fungi.