& V.A.O.Dittrich (Blechnaceae) Elaphoglossum laurifolium (Thouars) T.Moore (Dryopteridaceae) Lomariocycas palmiformis (Thouars) C.Chr. (Blechnaceae) Lycopodium diaphanum (P.Beauv.) Sw. (Lycopodiaceae) Notogrammitis billardierei (Willdenow) Parris (Polypodiaceae) Polyphlebium angustatum (Carmich.) Ebihara & Dubuisson (Hymenophyllaceae) Racomitrium lanuginosum (Hedw.) Brid. (Grimmiaceae) Rumohra adiantiformis (G.Forst.) Ching (Dryopteridaceae) Introduced plants Tristan da Cunha acquired an estimated 137 non-native vascular plants that can be categorized into four species types; weeds (trees, shrubs, agricultural weeds), grassland species (grasses), garden escapes (vegetables), and other ruderal species. Vascular plants were accidentally introduced in a variety of ways including; impurities in flower or vegetable seeds, seeds or plant fragments from other imported plants and in soil, attached to containers, cars or people. The majority of invasive weed species that has been introduced to the island are spread by seed and cover 50% of arable land in widely distributed patches. These species include prickly sow-thistle (Sonchus asper), smooth sow-thistle (Sonchus oleraceus), smooth hawksbeard (Crepis capillaris), scrambling fumitory (Fumaria muralis), green field speedwell (Veronica agrestis), groundsel (Senecio vulgaris), and nutgrass (Cyperus esculentus). Other invasive weed species that have a more localized distribution in plots include prickly sow-thistle (Sonchus asper), smooth sow-thistle (Sonchus oleraceus), smooth hawksbeard (Crepis capillaris), and groundsel (Senecio vulgaris). Whether a species is distributed locally or widely depends on the seed's dispersal mechanisms; larger seeds that have not adapted to wind dispersal will be distributed locally, while smaller seeds have adapted to wind dispersal will be widely distributed. The invasive plants have had several negative impacts on native island plant species, including the competitive exclusion of many such species. The out-competition will and can alter the structure of plant communities and the quality of the islands' soil. Introduced vegetation has altered long-term carbon storage as well as the reduction of CO2 in the atmosphere. Native plants such as fern bushes, Phylica bushes, fern brakes, mires, and bogs, contain high organic content matter which functions as storage for carbon. With the introduction of harmful species, the islands will see a decrease in carbon storage of both the soil and vegetation. With multiple changes occurring within the soil due to invasive plant species, the nutrient cycle is bound to be negatively influenced. Invasive plants are also affecting the human population of Tristan da Cunha by being disease carriers and becoming agricultural pests in gardens and pastures. The alien plants are able to survive and continue to grow and spread successfully on the islands because they