Epiphytes are:
a. Fungi that attack plants
b. Fungi that form mutualistic associations with roots
c. Nonphotosynthetic parasitic plants.
d. Plants that grow on other plants.

Verified step by step guidance

1. Understand the term 'epiphytes': Epiphytes are a type of plant that grows on another plant for physical support. They are not parasitic and do not harm the host plant.
2. Eliminate option a: Fungi that attack plants are typically parasitic and do not fit the definition of epiphytes.
3. Eliminate option b: Fungi that form mutualistic associations with roots are known as mycorrhizae, not epiphytes.
4. Eliminate option c: Nonphotosynthetic parasitic plants are not epiphytes, as epiphytes are typically photosynthetic and not parasitic.
5. Identify the correct option: Plants that grow on other plants without harming them are epiphytes, which corresponds to option d.

Key Concepts

Epiphytes

Epiphytes are plants that grow on other plants for physical support. Unlike parasitic plants, they do not derive nutrients from their host but instead obtain moisture and nutrients from the air, rain, and debris accumulating around them. Common examples include orchids and ferns found in tropical rainforests.

Parasitic Plants

Parasitic plants are those that derive some or all of their nutritional requirements from another living plant. They attach to the host plant through structures called haustoria, which penetrate the host's tissues to access water and nutrients. Examples include mistletoe and dodder.

Mutualistic Associations

Mutualistic associations refer to interactions between two different species where both benefit. In the context of fungi and plant roots, mycorrhizal fungi form mutualistic relationships with plant roots, enhancing water and nutrient absorption for the plant while receiving carbohydrates and other organic compounds in return.