National governments are increasingly adopting blockchain to enhance transparency, trust, and efficiency in public service delivery. However, evidence on how these technologies are governed across national contexts remains fragmented and overly focused on technical features. Using Polycentric Governance Theory, this study conducts a systematic review of peer-reviewed research published between 2021 and 2025 to examine blockchain-enabled public services and the institutional, organizational, and information-management factors shaping their adoption. Following PRISMA guidelines, we synthesize findings from major digital government and information systems databases to identify key application domains, including digital identity, electronic voting, procurement, and social services, and analyze the governance arrangements underpinning these initiatives. Our analysis reveals that blockchain adoption is embedded within polycentric environments characterized by distributed authority, inter-organizational coordination, and layered accountability. Rather than adopting full decentralization, governments typically utilize hybrid and permissioned designs that allow for selective decentralization alongside centralized oversight, a pattern we conceptualize as "controlled polycentricity." By reframing blockchain as a governance infrastructure that encodes rules for coordination and information-sharing, this study advances digital government theory beyond simple adoption metrics. The findings offer theoretically grounded insights for researchers and practical guidance for policymakers seeking to design and scale sustainable blockchain-enabled public services.