The herbarium of the Natural History and Science Museum at Porto University (PO) is a reference collection of Portuguese flora, comprising collections since the 19th century including former Portuguese colonies. All specimens deposited in this herbarium are readily accessible with meta-data (location and date of collection and name of collector). But some of the cryptogamic collections generated as secondary or opportunistic specimens in field surveys end up as unnamed or unpublished. This worsens when no documentation refers to these collections or when collections resulted from personal or casual collections made by botanists focused on vascular plants. PO African cryptogams comprise a total number of 3308 specimens (algae, fungi, lichens, bryophytes, pteridophytes). Some of these were the basis of new species to science or the first records for some countries, but 1484 are clearly understudied, being potentially interesting discoveries awaiting at the shelves. The main objective of this work was to recognize, repackage, numerate, and database these irreplaceable specimens. In this way, we hope to ensure their accessibility to staff and researchers. By presenting these collections, from a curatorship perspective, the associated missions, protagonists, and meta-data we hope to promote their study and application. We would like to acknowledge the support of the Portuguese Infrastructure of Scientific Collections - POCI-01-0145FEDER-022168 (PRISC.pt).