Polemonium caeruleum L.
Jacob’s ladder, Greek valerian, blue bells, American Greek valerian, charity
Jacob’s ladder is native to northern and central Europe and northern Asia. It is now naturalized in North America. The name “Jacob’s ladder” refers to the ladder-like spacing of its odd pinnate leaves.
Plants: Up to 1½′ (50 cm) high. The stem is branched.
Leaves: Odd pinnate—composed of groups of opposite leaves as well as a leaf on the end of the cluster. The clusters contain 7-11 leaflets. Leaflets are roughly oval-shaped, with smooth edges, about 1½″ (3.8 cm) long and ½″ (1.3 cm) wide.
Flowers: Large showy clusters of blue flowers appear on top. Flowers are blue, about 1″ (2.5 cm) in diameter, with five rounded petals.
Fruits: Capsules are ⅛–¼″ (5–7 mm). Seeds are brown, 1/16–⅛″ (3–3.5 mm).
Habitats: Margins of woods and swamps, damp grasslands, woodlands, meadows, and rocky areas, in temperate areas.
Online References:
From Lindman, Carl Axel Magnus, Bilder ur Nordens Flora, 1926. Scan from Projekt Runeberg. 
Polemonium caeruleum L. var. album hort.
5/15/2010 · Garden in the Woods, Framingham, Massachusetts · ≈ 7 × 9″ (18 × 21 cm) 
6/20/2021 · Highland Green, Topsham, Maine · ≈ 6 × 4″ (16 × 10 cm) 
A white-flowering cultivar, perhaps ‘Album’ · 6/20/2021 · Highland Green, Topsham, Maine · ≈ 7 × 4½″ (16 × 11 cm) 
A white-flowering cultivar, perhaps ‘Album’ · 6/20/2021 · Highland Green, Topsham, Maine · ≈ 6 × 4″ (16 × 10 cm) 
5/15/2010 · Garden in the Woods, Framingham, Massachusetts · ≈ 10 × 10″ (24 × 25 cm) 
5/15/2010 · Garden in the Woods, Framingham, Massachusetts · ≈ 9 × 9″ (22 × 23 cm) 
| Kingdom | Plantae | Plants, but not fungi, lichens, or algae (from Stearn's Botanical Latin) |
| Subkingdom | Tracheobionta | Vascular plants—plants with a “circulatory system” for delivering water and nutrients |
| Division | Magnoliophyta | Flowering plants, also known as angiosperms |
| Class | Magnoliopsida | Dicotyledons—plants with two initial seed leaves |
| Subclass | Asteridae | A large class that encompasses asters |
| Order | Ericales | Tea, persimmon, blueberry, Brazil nut, azalea, many others |
| Family | Polemoniaceae | Phlox, Jabob’s-ladder |
| Genus | Polemonium | Greek herbalist and healer Polemon of Cappadocia may be the source of this name |
| Species | caeruleum | “Sky blue”: the word “cerulean” derives from this |
Polemonium caeruleum description by Thomas H. Kent, not updated.
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