Prairie Loosestrife is a native, erect, perennial forb, growing one to two feet high on green ridged stems that are either simple or with some branching near the top.
The leaves are linear and firm with a single main vein, deeply depressed on the upper surface. Margins are entire but can be curled back. Leaf surfaces are free of hair and glands. They are not stalked. Tips are pointed to bluntly rounded. Lower stem leaves are largest - up to 3 1/2 inches long but only 1/4 inch wide. They decrease in size in the upper sections of the plant. Side branches may have little whorls of leaves in the branch axils. There may be fine cilia at the stem nodes where the leaves grow, but not as pronounced as on Fringed Loosestrife.
The inflorescence is a single flower or a cluster of up to 4 flowers at the ends of the upper stems. When there are four they form a whorl and hence the alternate common name of Four-flower Loosestrife and the species name.
Flowers are on long stalks, nodding, up to 1 inch wide. However, not all of the four that compose a whorl are open at one time. The calyx has 5 green lanceolate sharply pointed sepals which appear between the five yellow petals of the corolla. The petals may have some brown streaking of resin canals as the outer surface is glandular. Petals have rounded tips with somewhat ragged margins and a distinct point. The widest part is just above the middle. The five stamens have light yellow filaments, darker yellow crescent shaped anthers which turn a reddish-brown at maturity. These are weakly united at their bases, are shorted than the petals and surround a single style. False Stamens are present but extremely short.
The fruit is a round capsule up to 5.5mm in diameter, containing the numerous very small seeds which weigh 90,000 to the ounce. The capsule has the remains of the sepals and the style attached.
Habitat: Prairie Loosestrife grows from a root system composed of slender rhizomes and a mass of fibrous roots. It is not an aggressive spreader. Regeneration from seed requires at least 60 days of cold stratification or simply leaving them on the ground for a year. The plant prefers full sun, accepts partial shade, and needs wet to mesic soils. The plant is delicate so it can get overshadowed by larger neighbors.
Names: The genus name, Lysimachia, is from the Greek for either king Lysimachus or from lysis meaning "a release from" and mache is for "strife". The legend is that Lysimachus, king of Sicily, was walking through a field. A bull chased him. He grabbed a loosestrife plant, waved it in front of the bull and it calmed the bull. In general then, both the common and the generic name refers to a supposed power to sooth animals or "loose" them of their "strife". See notes below for more. The species name quadriflora, derived from quad for 'four' and flora, meaning 'flower' and thus means 'four-flowered', referring to the whorls of 4 flowers. The author name for the plant classification - ‘Sims’- is for John Sims (1749-1831), English botanist, first editor of Curtis’s Botanical Magazine, founding member of the Linnean Society, plant collector and author.
Comparisons: Several of our other native Loosestrifes have yellow corollas. Fringed Loosestrife, Lysimachia ciliata, has single flowers from the leaf axils and the corolla has a reddish eye in the center. Whorled Loosestrife, Lysimachia quadrifolia, has single flowers rising the leaf axils also, and there the leaves are broader and form a whorl of 4, hence the species name quadrifolia. Also, the corollas have the red eye and the petals from more of a star pattern.
Above: The inflorescence is a number of flower clusters at the end of the upper stems. While there are usually 4 flowers in a whorl they are not open at the same time.
Below: The yellow petals have somewhat ragged edges and an abrupt point. Sometimes brownish streaks are visible which are resin canals.
Below: The narrow green sepals are much shorter than the yellow petals. You can see one developing whorl of 4 flower buds. The seed capsule is round and usually smooth although there may be occasionally short glandular hair.
Above: The narrow leaves are many times longer than wide and stalkless with one central vein.
Below: The central vein is depressed on top and pronounced on the underside. Note the margin edges curving backward. The root is a mass of slender rhizomes and fibrous roots.
Prairie Loosestrife is found in Canada in Manitoba and Ontario, then south into the U.S. with the Dakotas on the western extremity of the range and New York on the eastern extremity - generally east of the Mississippi River excluding the gulf coast states and New England. Within Minnesota it is known in a wide band of counties across the southern 1/4th of the state, up to and into the metro area. Then another band of counties in NW Minnesota near the Red River Valley.
Family Change: This is one of 8 species of Lysimachia found in Minnesota, listed currently by DNR. Seven are native, one is introduced. Several others have been reported but with little data. Some of the leading references have moved the Lysimachia species into a new plant family - following the lead of Flora of North America, on the basis of resin canals among other considerations. The U of M Annotated Checklist of the Flora of Minnesota follows this classification. This genus was formerly in the plant family Primulaceae
Lore: As explained above, the common perception that the plant has soothing powers over animals led people to tie a branch to the yolk of oxen, making them easier to handle. The plant is known to repel gnats and other irritating insects which maybe explains why the animals were easier to handle. Pliny the elder wrote that the odor of loosestrife would keep snakes away.
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.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"