Which of the following is a species of salvia commonly used in ornamental gardening?

Salvia is indeed a genus that encompasses numerous species commonly utilized in ornamental gardening. This group includes various annuals and perennials, many of which are appreciated for their vibrant flowers, aromatic foliage, and ability to attract pollinators like bees and butterflies.

The genus Salvia is diverse, featuring species that can thrive in different garden conditions, from sun to partial shade, and that can tolerate drought, making them suitable for a wide range of ornamental landscape applications. Notable species in horticulture include Salvia nemorosa, known for its tall spikes of blue to purple flowers, and Salvia splendens, often seen in bright red or purple varieties and frequently used in annual bedding schemes.

The other options listed, while they are popular garden plants, do not belong to the Salvia genus. Lobelia is a separate genus known for its trailing habit and blue flowers. Ipomoea, commonly associated with morning glories and sweet potatoes, offers a different aesthetic with its fast-growing vines and colorful blooms. Petunia is a well-loved flowering plant, particularly for its range of colors and patterns, but it is not part of the Salvia genus. Hence, Salvia is correctly identified as the choice related to ornamental gardening within the provided options