The mycorrhizal roots of Pinus are associated with some fungal symbionts.

Mycorrhizal roots are a type of root system that form a mutualistic association with certain fungi. This symbiotic relationship benefits both the plant and the fungi involved. The mycorrhizal association enhances the plant's ability to absorb nutrients from the soil, particularly phosphorus, while the fungi receive carbohydrates from the plant.

Pinus and Mycorrhizal Association:
Pinus, commonly known as pine trees, are known to form mycorrhizal associations with certain fungi. In particular, they form ectomycorrhizal associations, which involve fungal hyphae forming a sheath around the root tips without penetrating the root cells.

Benefits of Mycorrhizal Association for Pinus:
1. Enhanced Nutrient Absorption: The fungal hyphae extend into the soil, greatly increasing the surface area available for nutrient absorption. This allows Pinus to access nutrients, such as phosphorus, that are typically less available in the soil.
2. Water Uptake: The mycorrhizal association also improves the plant's ability to take up water from the soil. The extensive fungal network helps in the absorption and transportation of water to the plant roots.
3. Disease Resistance: The fungi involved in the mycorrhizal association can provide a level of protection against soil-borne pathogens. They may compete with pathogens for resources or produce compounds that inhibit their growth.
4. Environmental Adaptation: The mycorrhizal association can help Pinus trees adapt to various environmental conditions, such as drought or nutrient-poor soils. The fungi enhance the plant's ability to withstand stress and improve its overall fitness.

Other Options:
- Cedrus: Cedrus, commonly known as cedar trees, also form mycorrhizal associations. However, the specific fungal symbionts may differ from those associated with Pinus.
- Cycas: Cycas, a type of gymnosperm, also forms mycorrhizal associations. However, the specific fungal symbionts may differ from those associated with Pinus.
- Ginkgo: Ginkgo, another gymnosperm, is known to form mycorrhizal associations. However, the specific fungal symbionts may differ from those associated with Pinus.

In conclusion, the mycorrhizal roots of Pinus are associated with certain fungal symbionts, forming an ectomycorrhizal association. This association provides numerous benefits to the plant, including enhanced nutrient absorption, water uptake, disease resistance, and environmental adaptation.