Palespike lobelia features nearly toothless, light green basal leaves, typically growing in a rosette formation. The leaves are somewhat oblong, ranging from 1 to 4 inches (2.5 to 10 cm) in length and 0.5 to 1.5 inches (1.3 to 3.8 cm) in width. They have a smooth texture with a slightly wavy margin and a pronounced midrib. The venation is pinnate, with a network of subtle secondary veins. The overall appearance is delicate and soft, aiding in the plant's identification.

Palespike lobelia flowers are distinguished by their vibrant colors, ranging from white to scarlet to blue. Each bloom is tubular and irregularly shaped, featuring a unique 5-part structure. These flowers have two distinct lips, adding to their distinctive appearance. The petals are arranged asymmetrically, enhancing the flower's irregular shape. They bloom in the summer months and can often be found in various habitats, exuding a subtle fragrance that attracts pollinators. Typical flower size is around 1 inch (2.5 cm) long.

The stem of palespike lobelia is initially densely downy near the base, tapering to a smooth texture higher up. The stem is slender, typically measuring around 1.5 to 3 feet (45 to 90 cm) in height. It is erect and can occasionally show slight branching but remains primarily simple in structure. The color ranges from green to purplish-green, with the lower dense hairiness providing a distinct textured feel that contrasts with the smoother upper portion.

The fruit of palespike lobelia is a dry dehiscent capsule that opens at maturity to release its small seeds. It typically measures around 0.3 inches (7-8 mm) in length. The capsule is generally oval-shaped, with a finely textured surface, transitioning in color from green to a light brown as it matures. These capsules are noteworthy for their bi-locular structure, meaning they are composed of two chambers, each containing numerous minute, dust-like seeds which are dispersed by wind upon the capsule's opening.