The influence of abiotic factors, such as temperature and edaphic factors, on seed germination and development, is well-known for plants. However, orchid seeds also require biotic components such as the orchid mycorrhizal fungi (OMF) which are often the determining factor for seed germination and protocorm development. Previous studies have shown that the OMF communities associated with Platanthera cooperi, native to the California Floristic Province, varied across populations and ontogeny. In roots of plants from the larger populations, the OMF Operational Taxonomic Units (OTUs) belonging to the family Tulasnellaceae (LT) were dominant while Ceratobasidiaceae (LC) OTUs were rare. Conversely, smaller populations showed the opposite pattern [OTUs from the smaller populations: Ceratobasidiaceae (SC) and Tulasnellaceae (ST)]. We hypothesize that native fungi and native temperature will enhance seed germination and protocorm development. We isolated and used the fungi representing the dominant and rare OTUs from large and small populations to test whether the fungi dominating the roots of plants in large and small populations, combined with the native soil temperature, providing a competitive advantage to the seeds belonging to the respective populations. Seeds from the large and small populations were exposed to the four fungal isolates (LC, LT, SC, ST) in combination with two temperature treatments (22C, 15.5C). Un-inoculated controls were also used as a fungal treatment. Consequently, the experiments included 20 treatment combinations, each of which was replicated 10 times. After 124 days of incubation, seed germination and protocorm development were recorded. We detected a three-way interaction among the seed provenance, OMF, and incubation temperature whereby the seeds from the small or large population inoculated with LT and incubated at 22C showed the highest germination. Furthermore, the highest protocorm formation was observed when seeds from the large population were inoculated with LC and ST and incubated at 15.5C, or when the seeds from either population were inoculated with SC at both temperature conditions, or when seeds from the small populations were inoculated with all fungi and incubated at 15.5C, indicating that the conditions required for germination and protocorm development are distinct. We showed that seed germination favored the warmer temperature, while protocorm development was enhanced at the cooler temperature.