One of these things is not like the others...
At first glance, this looks like the same plant in three different herbals. All three illustrations are labeled Acorus, which we know today as Acorus calamus, or sweet flag. It's an aquatic plant that doesn't bear a flower, and it has been used in traditional medicine around the world. But only the first illustration actually shows Acorus calamus.
The next two illustrations show a plant we know today as Iris pseudacorus, or yellow flag. It's native to Europe and is considered an invasive species in parts of the United States. It looks so much like Acorus calamus, that's how it got the name pseudacorus - but one of its distinguishing features is its yellow flower.
1: Dodoens, Rembert. Cruydt-Boeck. Inde plantijnsche druckerije van Françoys van Ravelingen, 1618.
2: Arnaldus de Villanova. Herbolarium de Uirtutibus Herbarum. [Impressum per Ioannem Rubeum & Bernardinū fratres Vercellenses, Anno Domini MDVIIII die XV Marcii], 1509.
3: Fuchs, Leonhart. De Historia Stirpivm Commentarii Insignes ... : Adiectis Earvndem Vivis Plvsqvam Quingentis Imaginibus ... Accessit ... Uocum Difficilium & Obscurarum Passim in Hoc Opere Ocurrentium Explicatio. In officina Isingriniana, 1542.