Fragrant False Indigo is a short perennial native shrub, much-branched, growing 12 to 18 inches tall with stems woody in the lower sections. Stems and twigs are usually free of hair but may have some fine appressed hair.
The leaves are alternate, compound with 6 to 15 pairs of leaflets plus a terminal leaflet, in total up to 3 inches long. Leaflets are alternate to sub-alternate, each about 1/2 inch long, oval to oblong, bluntly rounded to an abrupt pointed tip which is an extension of the main leaf vein beyond the margin of the leaflet. The base of the leaflet is less bluntly rounded, ending with a short stalk. The leaflets are mostly free from hair except along the margins, which are entire. The underside is gland-dotted; these glands produce a fragrance when the leaf is crushed. There are a pair of very small stipules at the base of each leaflet, which drop away during the season.
The inflorescence is a solitary dense spike, 1 to 3 inches long, of tubular pea-type flowers at the ends of the branching stems.
The flowers are 5-parted with a 5-toothed smooth calyx, green at the base, resolving to pinkish at the lobes, and a corolla which has a single rolled petal that forms first a tube and then opens, but remains rolled, to form the standard shielding beneath it the 9 to 10 stamens, pistil and style. This rolled petal is the typical banner (or standard) petal of a pea family flower. However, in the Amorphas, the laterals and keel petals are missing. The banner varies in color from pinkish to reddish with visible darker veining. The protruding bright stamens are quite noticeable with reddish filaments and reddish anthers at maturity. Flowers open from the base of the spike upward and are lightly fragrant.
Seed: Fertile flowers produce a small green pod with a smooth but glandular surface, that matures to a brown rough-surfaced tear-drop shaped seed about 5 x 3 mm. Seeds require a short period of cold stratification for germination.
Habitat: Fragrant False Indigo grows from a stout deep taproot. The plant does not spread vegetatively but instead by seed dispersal. It adapts to most soils, does best in full sun with mesic to dry conditions, but sandy soils are best avoided.
Names: The genus Amorpha, comes from the Greek amorphos, meaning 'shapeless or deformed' and refers to the single petal flower. The species name, nana, is from the Latin and means 'dwarf' referring to the short stature of this plant. The Amorphas are generally known as 'false indigos', hence the use of 'false' in many of the common names. 'Dwarf' because it is the smallest and 'smooth lead plant' because the other Leadplant (Amorpha canescens) has a hairy flower calyx. Eloise Butler sometimes referred to this plant as Amorpha microphylla, a term not longer accepted.
The author name for the plant classification - ‘Nutt.’ refers to Thomas Nuttall (1786-1859) English botanist who lived and worked in America from 1808 to 1841. On his many expeditions he collected many species that had been originally collected by Lewis and Clark but lost by them on their return journey. This species he collected in 1810-11 near the Mandan Villages in what is present day North Dakota.
Comparisons: The most look-a-like species is Leadplant, Amorpha canescens, which is typically much larger with flowers that are a deeper bluish-purple, with hair on the calyx and much more densely on the leaflets. The inflorescence of A. canescens will also have multiple spikes. A. fruticosa, Desert False Indigo resembles Leadplant but is much taller with leaves 4 to 8 inches long.
Above: Fragrant False Indigo is a low growing plant with woody stems, compound leaves and the flower raceme held above the leaves.
Below: The inflorescence is short - only 1 to 3 inches long, densely packed with flowers. The green seed pods show the 5-toothed calyx at their base. The underside of the leaves is paler in color with an intricate vein pattern and white margin hairs.
Above: The full leaf has 6 to 15 pairs of leaflets, usually sub-alternately attached, plus a terminal leaflet. The main leaf vein extends in a point beyond the rounded tip.
Below: Lower leaf surfaces are gland dotted. The root system forms a deep taproot.
Below: The flowers of Amorpha have only a banner petal, in this case rolled around the reproductive parts with the stamens exserted. Stamens are bright red at maturity. Note the deeper veining on the petal.
Below: The brown rough-surfaced seeds.
Fragrant False Indigo is not indigenous to the Garden but was introduced by Eloise Butler on Nov. 13, 1912 with 3 plants received from a Mr. Chase of Boulder Colorado where it is considered native. Martha Crone noted it in bloom in 1938, and planted it in Oct. 1945 and it was still in the Garden at the time of her 1951 Garden Census. Fragrant False Indigo is native in Minnesota to a band of counties along the western edge of the state - the counties that were formerly the prairie areas. The only remnant found in the metro area is Anoka County, but not Hennepin where the Garden is located. In North America, its range is restricted to the plains areas of MN, ND, SD, IA, NE, KS, OK, CO and NM. In Canada it is only known in Manitoba.
Fragrant False Indigo is one of three Amorphas found in Minnesota. The other two are A. fruticosa, Desert False Indigo and A. canescens, Leadplant.
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"