Arbutoids

Arbutoids refer to a form of mycorrhizal association found in certain members of the Ericaceae, particularly plants in the subfamily Arbutoideae such as Arbutus and Arctostaphylos. The term arbutoid mycorrhiza describes the symbiotic relationship between these plants and soil fungi, which enhances nutrient uptake and root health in often nutrient-poor environments.

The arbutoid mycorrhizal morphology is considered intermediate between ectomycorrhiza and ericoid mycorrhiza. Fungal partners typically form a mantle around the root tip and extend hyphae into the outer root tissues, with patterns that can resemble features of both major mycorrhizal types. The exact structure varies with host species and fungal partner, reflecting a continuum of forms rather than a single fixed architecture.

Fungal partners are diverse, including both basidiomycete and ascomycete lineages. The associations can involve fungi that are common in ectomycorrhizal communities as well as fungi more typically associated with ericoid or saprotrophic lifestyles. This diversity supports the host plants in acquiring nutrients, especially nitrogen and phosphorus, from challenging soils.

Ecologically, arbutoid mycorrhizae contribute to seedling establishment, plant vigor, and resilience in harsh environments such as Mediterranean-type climates and temperate forests. They influence plant community dynamics by facilitating nutrient cycling and enabling host species to occupy marginal habitats. Arbutoid mycorrhizae thus represent a distinct, but related, pathway in the continuum of plant–fungus symbioses.