Markush Groups: Traps For The Unwary

While many patent examiners prefer Markush claims, which recite lists of alternatively useable species, to be formatted as "selected from the group consisting of A, B, and C," Applicants should carefully consider claim construction before adopting this format. "A trap for the unwary claim drafter using Markush group language is the severely closed nature of a Markush group." 3-8 Chisum on Patents § 8.06 (2017).

Unless other language alters the meaning of a Markush clause, courts construe Markush groups as closed. See Multilayer Stretch Cling Film Holdings, Inc. v. Berry Plastics Corp., 831 F.3d 1350, 1358 (Fed. Cir. 2016) ("The presumption that a claim term set off by the transitional phrase 'consisting of' is closed to unrecited elements is at least a century old and has been reaffirmed many times by our court and other courts."). "[T]o overcome the exceptionally strong presumption that a claim term set off with 'consisting of' is closed to unrecited elements,