The Galápagos Islands are globally renowned for their ecological value and as a world symbol of scientific discovery; however this unique region currently has numerous ecological threats towards its native species. One of the threats is the detrimental impact of approximate 550 non-native plants introduced over that last 500 years of human presence in the archipelago.  In addition to these species with known arrival method, there are 62 vascular plants that have been classified as ‘doubtful natives’, where native status remains unclear.  The objective of this study was to provide a scientifically robust record of the doubtful native plant species in the Galápagos Islands and provide information on their baseline natural variability and abundance.  The aims of the analysis were three-fold.  Firstly, to examine the use of plant macrofossil analysis in determining the origins of doubtful native species on the Galápagos Islands.  The second aim of this study was to determine the timing of arrival of doubtful natives.  The third aim was to examine the natural variability and abundance of doubtful natives through time.

Results/Conclusions

To help address the questions of origins regarding these doubtful-natives and their impact on highland ecosystems over the past 500-1000 years, we analyzed plant macrofossils in sedimentary records. Appropriate species’ classification (native or introduced) was determined using baseline data of species presence on the islands.  We determined six plants (Ageratum conyzoides, Solanum americanum, Ranunculus flagelliformis, Brickellia diffusa, Galium canescens, Anthephora hermaphrodita) once considered doubtful-natives or introduced are actually native to the Galápagos flora.  All of these species were present over 1000 years prior to human arrival, which provides clear evidence of the plants’ native status. In addition to the ‘doubtful native’ findings, seeds have been discovered from an aquatic species (family Elatinaceae genus Elatine) previously unknown in Galápagos in the fossil record.  Current work is exploring the exact time of disappearance from the islands and the previous distribution of the Elatine sp. on two of the main islands, Santa Cruz and San Cristobal.  The use of long-term historical baseline data is a valuable tool that can be directly applied to conserving and restoring the native biodiversity in Galápagos.