The Polemonium genus covers a large number of plants commonly known as "Jacob's Ladder". Polemonium reptans, while still referred to as "Jacob's Ladder" is more correctly named "Greek Valerian" or "Spreading Jacob's Ladder" as it can root from the stems.
Greek Valerian is a native mostly erect perennial forb growing 8 to 20 inches high on slender stems that frequently recline. There is some branching near the top. Stems are light green but can be reddish green, usually smooth, with angled sides.
The leaves are alternate and pinnately-divided into 7 to 17 oblong leaflets, each leaflet up to 1-1/2 inches long. A terminal leaflet creates the odd number of leaflets. Leaflets are medium green in color, with smooth edges, usually no hair on the upper surface, and usually not stalked. The upper leaves within the the inflorescence usually have only 3 to 5 leaflets, sometimes just a simple leaf. The underside of the leaflet is paler in color with some fine hair.
The inflorescence is a loosely branched panicle with just a few flowers per branch, arising at the top of the stems and held above the leaves.
The flowers are bell shaped with 5 blue-violet petals that spread slightly. (White albinos are known to occur.) The calyx is light green, sometimes with reddish tints, sometimes with fine hair. Its five lobes are triangular. There are five stamens with whitish filaments and pale yellow anthers. There are not exserted - not longer than the petals. The single style is longer and has a 3-parted stigma.
Seed: Fertile flowers produce a dry 3-chambered seed capsule with about 3 seeds in each chamber. Seeds require 60 days of cold stratification for germination.
Habitat: Greek Valerian or Spreading Jacob's Ladder grows in the rich soils of open woods, slopes, shaded banks. While it may tolerate full sun, it will do best in light shade to dappled sun such as under a high tree canopy. For best bloom it needs soils that are moist to mesic. The stems may root if they lay on the ground. The root system is fibrous with a small crown. It also spreads by reseeding.
Names: The genus name Polemonium is a bit obscure but according to Stern (Ref. #37a) comes from the Greek pŏlĕmōniŏn which referred to an old medicinal plant thought to have a connection back to the Greek philosopher Polemon of Cappadocia. The species name, reptans, refers to having creeping or rooting stems. The name 'Jacob's Ladder' is an old biblical reference to the leaflets forming 'a ladder to heaven'. The author name for the plant classification - 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: Several species are similar to P. reptans. P. occidentale [photo below] and P. vanbruntiae have brighter flowers with stamens exserted beyond the petals which are wider spreading. The garden variety of Jacob's Ladder sometimes sold with the scientific name P. caeruleum and sometimes with the other scientific names and called "Greek Valerian" or "Jacob's Ladder" has fewer narrower leaves, blue flowers and seed capsules without stalks. These are not native species.
Above: 1st & 2nd photos - Jacob's Ladder around the 1st of June. The inflorescence is a loosely branched panicle with each branch have just a few flowers. All are held above the leaves. 3rd photo - The 5-lobed calyx can have purplish tint as seen here and also fine hair.
Below: 1st photo - Seed pods of late August. Each capsule has 3 chambers. 2nd photo - The leaves are pinnate with 7 to 17 oblong leaflets. The underside (3rd photo) is pale in color with fine hair. Leaves near the top of stems have a reduced count of leaflets as seen in the photo far below.
Below - comparison: 1st photo - The corolla is bell shaped with 5 petals. The five stamens have whitish filaments and light yellow anthers. There is a single style with a 3-lobed tip. 2nd photo - An example of the flower of Western Jacob's Ladder, P. occidentale, the only other species of the genus native to Minnesota.
Below: The root system and crown of Jacob's Ladder.
Notes: Eloise Butler first recorded introducing Greek Valerian to the Garden with plants obtained in 1910 and 1911, both times sourced from Lake City, MN. Her log refers to it as "Greek Valerian". More were added in 1921, '27, and '29. Martha Crone sowed seeds and added plants: Seeds in 1942, '44, and '53 and plants in 1947, '48, and '54. P. reptans is native to the SE corner of Minnesota up to and including some of the metro counties. In North America it is found in the eastern half of the continent, excepting a few gulf coast states and Maine in the U.S. and is found in the Canadian provinces on Ontario and Quebec, but classified there as an exotic. It has been replanted at various time, most recently in 2012.
Jacob's Ladder is available from nurseries and native plant growers. Certain new varieties that are not the native species can bloom all summer.
There are two species of Polemonium native to Minnesota - P. reptans, Spreading Jacob's Ladder and P. occidentale subsp. lacustre, Western Jacob's Ladder. The latter is rare, endangered, and occurs only in four locations in the coniferous forests of northern Minnesota and then two in Wisconsin, making up the entire known population in North America.
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"