Hawaiʻi is characterized as having both one of the most unique and one of the most threatened floras in the world. With 1,369 currently recognized native vascular plant taxa, 1,232 of which are endemic, the proportion of vascular plant endemism is nearly 90%. Preliminary conservation assessments indicate that 72-100% of native Hawaiian plant taxa are likely to be threatened with extinction. Modelled after the Global Strategy for Plant Conservation (GSPC), the Hawaiʻi Strategy for Plant Conservation (HSPC) was created in 2014 to help guide the urgent conservation work required to protect the unique flora of Hawaiʻi. The work that is part of this PhD thesis primarily addresses Targets 2 and 4 of the HSPC, which are focused on conducting conservation assessments to guide conservation action and conducting applied research to inform conservation practice, respectively. In chapter I, we synthesized the threatened status of the Kauaʻi single-island endemic (SIE) vascular plant flora based on IUCN Red List of Threatened Species assessments. The assessments revealed that 90% of the 256 taxa are threatened with extinction and the remaining 10% are already extinct or extinct in the wild. We explored how the proportion of threatened taxa based on the Red List assessments compares with local and national assessments and how these assessments are and will continue to be useful for conservation planning in Hawaiʻi. Chapter II is an example of an updated assessment for one of the taxa, Brighamia insignis, which was confirmed as extinct in the wild after the work for chapter I was completed. In chapter III, we tested whether similar in situ sampling strategies aimed at capturing targeted levels of genetic diversity for conservation can be applied to closely related species in the same genus. Our study revealed that the same sampling method does not always equate to similar genetic diversity captured and that most of the collections for species are not adequately representative of the genetic diversity remaining in the wild, particularly the two Hawaiian taxa we included. Chapters IV, V, and VI made a case for and demonstrated how adapting many of the approaches and tools that zoos have developed to manage animals across multiple zoos to how threatened plant species are managed across multiple botanic gardens can greatly improve the health of collections. Chapter VII is an observational study to gain a better understanding of a plant-pollinator interaction between the non-native plant species banana poka (Passiflora tarminiana) and two endemic Hawaiian forest bird species. Although banana poka is invasive and often targeted for removal in native dominated forests, it may form a substantial component of the diet of two bird species, but it also remains unclear whether its presence may also decrease visitation to co-occurring native plant species. Chapters VIII and IX assessed seed germinability related to different abiotic and biotic factors. In the case of chapter VIII, how germinability of a suit of Hawaiian coastal plant species is affected by increased salinity and in chapter IX, how various climatic variables and collection localities based on generalized provisional seed zones are correlated with germinability for the most ecologically important and now threatened native Hawaiian tree, species of Metrosideros on Kauaʻi. Results of the former can help inform coastal conservation and restoration management decisions in the face of climate change and the latter for collection planning for future restoration. In chapter X, we applied the framework of the Global Tree Assessment initiative to the flora of Limahuli Valley on Kaua‘i. One of our main takeaways was that trees only constitute about 40% of the flora in Limahuli Valley so it is equally important to also consider and prioritize other plant species for restoration, including ferns which are often overlooked. Like chapter X, the results of chapter XI will also help inform species conservation prioritization since the need for prioritization tools is so great with such a high percentage of our flora that is threatened with extinction. Using the Kaua‘i SIE angiosperm flora as a study system, we found that shorter taxa, smaller leaves, and lower initial seed germinability were significantly correlated with taxa that have fewer numbers of individuals remaining in the wild. The phylogenetic tree created and trait data compiled for the study will be a tremendous resource for further research in Hawai‘i as well. Finally, in chapter XII, we present how botanical field exploration just in the past several years has resulted in native plant species ranges to be extended and species once thought to be extinct to be rediscovered. There is still so much to be discovered about native plants in Hawai‘i through additional field exploration alone and the need for applied research to help inform conservation management for these plants cannot be overstated.