Many lichen fungi reproduce sexually by forming ascocarps or rarely, basidiocarps. Lichen algae reproduce independently by asexual cell division. Formation of soredia - specialized reproductive structures that are small clusters of hyphae with embedded algae. Though most evidence points to a mutualistic symbiosis, some debate that the relationship may actually be parasitic. The argument for mutualism is that fungi benefit the algae and that lichens can survive in habitats that are inhospitable to either organism alone.
Lichens are important pioneers, breaking down rock and allowing for colonization by other plants.
Some can tolerate severe cold. Lichens are sensitive to air pollution due to their mode of mineral uptake. Mycorrhizae Mycorrhizae are specific, mutualistic associations of plant roots and fungi. The fungi increase the absorptive surface of roots and exchanges soil minerals. Are necessary for optimal plant growth.