This paper presents Yggdrasil a sharding solution for permissionless blockchains that supports both payment transactions and general Ethereum-like smart contracts. Yggdrasil allows to split and merge shard dynamically leveraging decentralized mechanisms to assign nodes to shards in a secure way. A new 2PC protocol allows to guarantee the execution of smart contracts distributed across different shards even when shards dynamically re-organise. An experimental study confirms the capability of Yggdrasil to scale and to adapt to transaction load.