Blue Giant Hyssop is an erect native perennial forb growing from 2 to 4 feet high on sturdy green 4-angled stems. Stems occasionally branch near the top and can be with or without stem hair.
The leaves are opposite, somewhat triangular heart-shaped, with coarse teeth, medium green, with prominent veining and mostly on short stalks. The leaf underside is whitish with fine hair. Teeth on large lower leaves may be somewhat rounded. Leaves have anise scent when crushed or brushed.
The inflorescence is a dense spike, up to 8 inches high, of whorl-like flowers at the top of stems, sometimes interrupted as shown in the photo below. In the mint family this arrangement is called a 'verticillaster' where the flowers look like a whorl arrangement but are actually in cymes that rise from the axils of opposite bracts. Large plants can produce many spikes. Flowers open in various spots around the spike, not from the bottom to the top. The flowers are very aromatic with an anise scent.
The small flowers are 5-parted, about 1/3 inch long with a calyx that forms a tube with 5 sharply pointed teeth. The tube ranges from light blue to violet in color with the upper part the darkest. Several darker vein lines are often visible on the calyx. The corolla is similar in color but much lighter and slightly longer than the calyx. The lips of the corolla end with two lobes on top and three on the bottom. Protruding from the corolla are 4 stamens with white filaments and violet-purple anthers and a single white style with a bifurcated tip. Very delicate purplish vein lines are seen inside the corolla throat. Flower clusters in the spike are interceded with ovate light green floral bracts. Many species of bees are attracted to the flowers.
Seed: Fertile flowers produce a dry nutlet containing one oblong brown seed about 1 mm x 2 mm. These disperse by wind shaking the stem. Seeds are small and need light for germination plus 30 days of cold stratification. Seeds that fall from the plant will readily self-germinate in the Spring and the seedlings transplant easily and larger ones will flower the same year. American Goldfinches are quite fond of the seeds, even in the green stage.
Habitat: Blue Giant Hyssop grows best in sandy to loamy soils in full to partial sun with mesic to dry-mesic moisture conditions. The fibrous root system produces a small taproot. Good specimens are found in the Upland Garden on Prairie Path. It is generally available from nurseries that supply native plants.
Names: The common names are referring to "fragrant" and "anise" because the leaves have a fragrant anise odor when crushed, green or dry. The genus Agastache is derived from two Greek words - agan, meaning 'very much' and stachys, meaning 'an ear of wheat' which together refer to the flower spikes of this genus having many flowers, like grains of wheat. The species foeniculum, is from the the Latin word for Fennel, used here to represent a plant that produces a fragrant scent. The author names for the plant classification cover two people; first ‘(Pursh)’ is for Frederick Traugott Pursh (1774-1820) German-American botanist who wrote A Systematic Arrangement and Description of the Plants of North America, and was the botanist who catalogued and described the plants brought back by the exploring expedition of Lewis and Clark. His work was revised by Otto Kuntze (1843-1907) German botanist, who edited the collections in Berlin and Kew Gardens and then published Revisio Generum Plantarum which laid out new rules for nomenclature which were ejected at the time by his peers but some acceptance came long after his death. An older scientific name for this species is A. anethiodora.
Comparisons: A similar looking plant but taller, and whose flowers have a green calyx is Purple Giant Hyssop, A. scrophulariifolia.
Above: The inflorescence. Flowers open in various spots around the spike, not from the bottom to the top. Each flower cluster is subtended by a small green bract. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Below: 1st photo - an example of an interrupted inflorescence. 2nd photo - upper stem leaves are smaller and have sharp coarse teeth rather than the rounded teeth of the lower leaves. 3rd photo - the fibrous root system.
Below: 1st photo - The top side of a large lower leaf showing more rounded teeth. Note the prominent veining on both sides. 2nd photo - the whitish underside of the leaf.
Below: 1st photo - Very delicate purplish vein lines are seen inside the corolla throat as well as on the outside of the calyx. 2nd photo - Each dry seed capsule contains one oblong 1 mm x 2 mm hard brown seed.
Below: Axillary racemes.
Below: The inflorescence of mature plants frequently develops axillary racemes from the upper leaf axils.
Below: Stands of Blue Giant Hyssop attract a wide range of bees and then American Goldfinches as the seeds form.
Notes: Blue Giant Hyssop is native to most of Minnesota except the far south tier of counties and parts of the more dry Southwest section of the State. It is not indigenous to the Garden. Eloise Butler first planted it in the Garden on Oct. 21, 1908 with roots obtained from the area of Minnehaha Park in Minneapolis; then again in Sept. 1918 with plants from Washburn Park. Martha Crone planted it in 1945 and '47 and seeds in 1953; and it is listed on her 1951 census of plants in the Garden under the older classification of A. anethiodora. This plant is on the "endangered list" in Iowa. Within North America it is generally found north from Colorado, Nebraska, Iowa, Illinois and Pennsylvania and up into the lower Canadian Provinces.
Agastache foeniculum is one of three members of the Agastache genus known in Minnesota, The other two are A. nepetoides, Yellow Giant Hyssop, which is rare and not collected since 1938, and A. scrophulariaefolia, Purple Giant Hyssop.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"