Purple Giant Hyssop (Agastache scrophulariifolia)
Spelled A. scrophilariaefolia in Gray. Not a terribly common plant around here; this patch was growing in a clearing in Scott, where it was blooming in late August. The flowers are irresistibly attractive to butterflies. The leaves have a noticeable anise scent, not as strong as but very much like the scent of its more commonly cultivated cousin, Anise Hyssop (A. foeniculum). The two species are very similar; the most obvious difference is in the length of the flower spikes, which in A foeniculum are usually not much longer than your thumb, but in this species can easily exceed your longest finger.
Gray describes the genus and the species:
AGÁSTACHE Clayt. GIANT HYSSOP. Calyx tubular-bell-shaped, 15-nerved, oblique, 5-toothed, the upper teeth rather longer than the others. Upper lip of corolla nearly erect, 2-lobed, the lower 3-cleft, with the middle lobe crenate. Stamens 4, exserted; the upper pair declined, the lower and shorter pair ascending, so that the pairs cross; anther-cells nearly parallel. —Perennial tall herbs, with petioled serrate leaves, and small flowers crowded in interrupted terminal spikes in summer. (From agan, much, and stachys, an ear of corn, in reference to the numerous spikes.) Lophanthus Benth., in part.
A. scrophulariaefòlia (Willd.) Ktze. Stem (obtusely 4-angled) and lower surface of the ovate or somewhat heart-shaped acute leaves slightly pubescent: spikes 0.6-5 dm. long; calyx-teeth lanceolate, acute, shorter than the purplish corolla; otherwise like the preceding [A. nepetoides]. (Lophanthus Benth.)—N. H. to Out., Mo., Ky., and Va. Var. Mollis (Fernald) Heller. Stems and lower surfaces of leaves densely villous. — Vt. and Ct. to Ill.
[Because Gray’s description of this species refers to his description of A. nepetoides, here is that description:
A. nepetoides (L.) Ktze. Stem stout, 0.7-1.5 m. high, sharply 4-angled, smooth or nearly so; leaves ovate, somewhat pointed, coarsely crenate-toothed, 6-12 cm. long; spikes 3-12 cm. long, crowded with the ovate pointed bracts; calyx-teeth ovate, rather obtuse, little shorter than the pale greenish-yellow corolla. (Lophanthus Benth.) — Borders of woods, e. Mass., Vt., and w. Que. to Minn., and southw.]
The famous naturalist William Bartram found this species in New Jersey near Philadelphia, and reported it as Hyssopus scrophularifolius in his Copendium Florae Philadelphicae:
H. spikes verticillatc, cylindric; styles longer than the corolla; leaves cordate-ovate, acuminate, obtusely dentate.—Wilhl. and Pursh.
Agastache, Gronovius, Fl. Virg. 88.
Icon. Herm. parad. t. 106.
A very rare plant, easily known from the preceding [Agastache nepetoides]. From fourteen inches to two feet high. Flowers purple. On the banks of the Delaware, Jersey side, on the walk from Kaighn’s point to the next ferry below, close to a shady thicket. Perennial. July.