This showy perennial is usually unbranched, but may occasionally show some branching.

The upright stems bear lavender-blue, tubular flowers, densely packed at the top of the stem. Striking, bright blue flowers are located in the axils of leafy bracts and form an elongated cluster on a leafy stem. Each flower is divided into two lips – the upper lip has two segments and the lower lip three.

This blue counterpart to the Cardinal Flower (Lobelia cardinalis) is a highly sought-after plant for woodland gardens, especially as it blooms bright blue in late summer.

The unfortunate species name siphilitica refers to its supposed use as a remedy for syphilis.