A "Markush" claim recites a list of alternatively useable members.
In re Harnisch, 631 F.2d 716, 719-20 (CCPA 1980); Ex parte Markush, 1925
Dec. Comm'r Pat. 126, 127 (1924). The listing of specified alternatives
within a Markush claim is referred to as a Markush group or Markush grouping.
Abbott Labs v. Baxter Pharmaceutical Products, Inc., 334 F.3d 1274, 1280-81,
67 USPQ2d 1191, 1196-97 (Fed. Cir. 2003) (citing to several sources that
describe Markush groups). Claim language defined by a Markush grouping
requires selection from a closed group "consisting of" the alternative
members. Id. at 1280, 67 USPQ2d at 1196. See MPEP ยง 2111.03, subsection II, for a discussion of the term "consisting of" in the context of Markush groupings.
....
A Markush grouping is proper if the members of a group share a single structural similarity and a common use. See subsections II - IV, below, for guidelines regarding the determination of whether a Markush grouping is improper.