A merged shape file of all the layers in the The World Geographical Scheme for Recording Plant Distributions Edition 2 R.K. Brummitt Plant Taxonomic Database Standards No. 2 Edition 2, October 2001 (Permanent IRI: http://www.tdwg.org/standards/109, github project: https://github.com/tdwg/wgsrpd)
Original shapefiles for layers 1 - 4 are provided in the above linked github project.
The shapefiles for layers 1, 2, 3 and 4 in this project may not be up to date to the latest updates to the second edition but should conform to the TDWG Areas vocabulary provided in the CDM model (https://github.com/cybertaxonomy/cdmlib/blob/master/cdmlib-model/src/main/resources/terms/TdwgArea.csv)