Blue giant hyssop

Conservation Status

IUCN Red List

not listed

NatureServe

NNR - Unranked
SNR - Unranked

Minnesota

not listed

Description

Blue giant hyssop, also called anise hyssop, is a 24″ to 36″ tall, erect, perennial forb that rises from a taproot.

The stems are erect, square, and occasionally branched above the middle. They are usually hairless, sometimes slightly hairy.

The leaves are opposite, egg-shaped to triangular egg-shaped or rhombic egg-shaped, up to 3½″ long, and up to 2″ wide. They are on leaf stalks that are no more than ⅝″ long. The leaf blades are broadly angled or squared off at the base and tapered to a point at the tip with straight or concave sides along the tip. The upper leaf surface is dull green and hairless. The lower surface is whitish due to a dense covering of microscopic, fine hairs. The hairs are barely discernible when using a hand lens with 10x magnification. The margins are coarsely toothed with sharp, forward-pointing teeth. The leaves emit a strong, anise-like odor when crushed.

The inflorescence is a dense spike at the end of the stems and branches. The spikes are up to 6″ long, ¾″ to 1″ wide including the corollas, and are often interrupted at the base. The flowers are arranged in dense whorls that are subtended by hairless, broadly egg-shaped, abruptly tapered, inconspicuous bracts.

The individual flowers are about ½″ long. There are 5 dull blue-violet sepals fused onto a ¼″ to ⅜″ long calyx tube with 5 lance triangular-shaped lobes. The calyx tube is minutely hairy when in flower. There are 5 petals fused into a funnel-shaped corolla tube with a 2-lobed upper lip and a 3-lobed lower lip. The corolla is blue and extends well beyond the calyx. There are 4 stamens with purple anthers that protrude well beyond the corolla. After the corollas drop off, the spike that remains is blue-violet, not green or whitish. There is no floral scent.

The fruit is a more or less 3-sided nutlet.

Height

24″ to 36″

Flower Color

Blue-violet

Similar Species

Purple giant hyssop (Agastache scrophulariifolia) is a much taller plant, 36″ to 60″ in height at maturity. The underside of the leaves are green, not white. The calyx is green and hairless. The individual flowers are white or pale pink to purple. The spike that remains after the flowers have dropped is green or whitish, not blue-violet.

Habitat

Dry to moderate moisture. Upland woods and prairies. Full or partial sun.

Ecology

Flowering

July to August

Pests and Diseases

Use

Distribution

Sources

2, 3, 5, 7, 24, 28, 30, 83.

Biodiversity occurrence data published by: Minnesota Biodiversity Atlas (accessed through the Minnesota Biodiversity Atlas Portal, bellatlas.umn.edu. Accessed 9/9/2026).

Midwest Herbaria Portal. 2026. https://midwestherbaria.org/portal/index.php. Accessed 9/9/2026.

Agastache foeniculum (Pursh) Kuntze in Bánki, O., Roskov, Y., Döring, M., Ower, G., Hernández Robles, D. R., Plata Corredor, C. A., Stjernegaard Jeppesen, T., Örn, A., Pape, T., Hobern, D., Garnett, S., Little, H., DeWalt, R. E., Miller, J., Orrell, T., Aalbu, R., Abbott, J., Abreu, C., Acero P, A., et al. (2026). Catalogue of Life (2026-07-17 XR). Catalogue of Life Foundation, Amsterdam, Netherlands. https://doi.org/10.48580/dgykv