Agastache scrophulariifolia (Willd.) Kuntze

Purple Giant Hyssop


CC = 9
CW = 5
MOC = 6
SRank = S1

© SRTurner

Family - Lamiaceae

Habit - Perennial forb with fibrous roots and sometimes short rhizomes.

Stem - Ascending to erect, to 1.5 m, stout, sharply 4-angled, moderately to densely pubescent with more or less spreading, multicellular hairs.

Agastache_scrophulariifolia_stem.jpg Stem and node.

Stems are usually hairy.

© SRTurner

Leaves - Opposite, petiolate. Petioles 0.8-6.0 cm long. Leaf blades 2-15 cm long, the upper surface moderately pubescent with short, relatively stiff hairs along and between the veins, the undersurface moderately to densely pubescent with finer, somewhat crinkled, more or less spreading hairs, and also with inconspicuous, sessile glands.

Agastache_scrophulariifolia_leaf1.jpg Leaf adaxial.

© SRTurner

Agastache_scrophulariifolia_leaf1a.jpg Leaf adaxial surface.

© SRTurner

Agastache_scrophulariifolia_leaf2.jpg Leaf abaxial.

© SRTurner

Agastache_scrophulariifolia_leaf2a.jpg Leaf abaxial surface.

© SRTurner

Inflorescence - Dense, terminal, cylindrical spikes 3-17 cm long, 1.5-2.5 cm in diameter, the bracts elliptic-ovate to nearly circular, shorter than to more commonly slightly longer than the calyces.

Agastache_scrophulariifolia_inflorescence.jpg Inflorescence.

© SRTurner

Flowers - Calyces 4.0-6.5 mm long, green with the lobes often pale pinkish-tinged, the lobes 2.0-2.5 long at flowering (to 3.2 mm at fruiting), ovate, angled to bluntly to sharply pointed tips. Corollas zygomorphic, 5-8 mm long, light pinkish purple to pale bluish purple or less commonly white. Stamens 4, strongly exserted, the lower 2 stamens with slightly shorter filaments that are slightly curved under the upper corolla lip, the upper 2 stamens with slightly longer, straight filaments (angled slightly downward), the anthers small. Ovary deeply lobed, the style appearing nearly basal from a deep apical notch. Style exserted, more or less equally 2-branched at the tip.

Agastache_scrophulariifolia_flowers1.jpg Flowers.

© SRTurner

Agastache_scrophulariifolia_flowers2.jpg Flowers.

© SRTurner

Agastache_scrophulariifolia_calyces.jpg Calyces.

© SRTurner

Fruits - Dry schizocarps, separating into usually 4 nutlets, these 1.2-1.5 mm long, oblong-obovoid to oblong-ellipsoid, the surface yellowish brown, densely and minutely hairy at the tip, otherwise glabrous and slightly roughened.

Flowering - July - September.

Habitat - Bottomland forests and forest openings, streambanks, swales in mesic upland prairies, roadsides. Sometimes cultivated.

Origin - Native to the U.S.

Lookalikes - None.

Other info. - This beautiful species is rare in Missouri, with only three specimens being collected from the wild within the past century. It may well be waning in Missouri. It is more common in the upper Midwest and ranges into New England and Canada. The plant is recognized by its opposite, petiolate leaves and cylindrical inflorescences of bluish flowers. As is the case with the far more common A. nepetoides, the flowers do not all open at once, but rather at seemingly random spots within the spike over a period of time.

The above photos were taken of plants in a managed native plant bed. It is possible that they represent a horticultural variant, though most characters match the botanical descriptions. Wild types usually have hairier stems.

Photographs taken at Prairie Fork Conservation Area, Callaway County, MO, 10-18-2021 (SRTurner).