Historical herbarium collections have been proposed as a last resort for recovery of extinct plant species not represented in dedicated seed banks or other living conservation collections. For critically endangered plants at the brink of extinction, herbarium collections may also contain historical material from extinct subpopulations representing a species' former range and lost genetic diversity of high value for conservation management. We explored the potential for germination of 81 critically endangered seed plant taxa endemic to the Hawaiian island of Kauaʻi from herbarium specimens in herbarium PTBG of the National Tropical Botanical Garden (NTBG). Of 1250 recorded specimens of wild origin, 138 specimens representing 37 taxa contained mature seeds that could be subjected to germination testing. Seven of these taxa were not represented by any NTBG seed bank collections. Fresh embryos were observed in one seed of each of the three species Schiedea helleri, Schiedea kauaiensis and Viola helena. While potential germination success may be low, we conclude that testing of seeds from herbarium collections should be extended from a focus on strictly extinct taxa to critically endangered taxa, which may not have sufficient representation in seed banks or other living collections of subpopulations and genetic diversity across their wild range.