contain the highest diversity of endophytic organisms that possess novel and diverse chemical metabolites. It has been estimated that there could be approximately 1 million endophytic fungi that exist in the world. A diazotrophic bacterium isolated in lodgepole pines (Pinus contorta) in British Columbia, Canada, is Paenibacillus polymyxa, which may help its host by fixing nitrogen. Classification Endophytes include a wide variety of microorganisms including fungi, bacteria and viruses. There are two different means of classifying endophytes. Systemic and non-systemic The first method divides endophytes into two categories: systemic (true) and nonsystemic (transient). These categories are based on the endophyte's genetics, biology, and mechanism of transmission from host to host. Systemic endophytes are defined as organisms that live within plant tissues for the entirety of its life cycle and participate in a symbiotic relationship without causing disease or harm to the plant at any point. Additionally, systemic endophytes concentrations and diversity do not change in a host with changing environmental conditions. Non-systemic or transient endophytes on the other hand vary in number and diversity within their plant hosts under changing environmental conditions. Non-systemic endophytes have also been shown to become pathogenic to their host plants under stressful or resource limited growing conditions. An example of this would be Colletotrichum fioriniae, which is an endophyte of many temperate broadleaved trees and shrubs, but can also be a pathogen on many fruits and some leaves. Clavicipitaceous and non-clavicipitaceous The second method divides fungal endophytes into four groups based on taxonomy and six other criteria: host range, host tissues colonized, in planta colonization, in planta biodiversity, mode of transmission and fitness benefits. These four groups are divided into clavicipitaceous endophytes (Class 1) and non-clavicipitaceous endophytes (Class 2, 3, and 4). Class 1 endophytes are all phylogenetically related and proliferate within cool and warm season grasses. They typically colonize plant shoots where they form a systemic intercellular infection. Class 1 endophytes are mainly transmitted from host to host by vertical transmission, in which maternal plants pass fungi on to their offspring through seeds. Class 1 endophytes can further be divided into Types I, II and III. Among these three types of clavicipitaceous endophytes are different interactions with their plant hosts. These interaction range from pathogenic to symbiotic and symptomatic to asymptomatic. Type III clavicipitaceous endophytes grow within their plant host without manifesting symptoms of disease or harming their host. Class 1 endophytes typically confer