There is no such thing as Gypsum weed! The correct lyric is 'Jimpson weed' which is a common weed in open fields and prairies. Jimpson weed (Datura stramonium) is a large plant 4 feet or more tall with fetid smelling beautiful purple flowers and large very thorny seed pods. It is a member of the Nightshade family and seeds contain a lot of alkaloids so some idiots use them as hallucinogens. Was a very common Gene Autry song in all of his radio and television career as it expressed the love of the cowboy for the wide open range. As a young child back in the late '40s and early 50s I recall listening to it on the radio and later on television as the opening song for 'The Gene Autry Show'. I think I actually prefer 'Tumbling Tumbleweeds' a bit better, especially as performed by 'The Sons of the Pioneers'.