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 shorter than the petals and surround a single style. False Stamens are present but extremely short.
The fruit is a round capsule up to 5.5 mm in diameter, containing the numerous very small seeds which weigh 90,000 to the ounce. They need light and at least 60 days of cold stratification for germination, or simply leaving them on the ground to overwinter. 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. 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: Prairie Loosestrife was formerly slotted into the Primrose family (Primulaceae), but the change to Myrsine is explained at the page bottom. 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 soothe 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 of 1803 - ‘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. While Sims original classification still holds, others tried to reclassify the species using the following names which are now not accepted: Steironema quadrifolium, Steironema longifolium, Lysimachia longifolia, L. revoluta, and Nummularia longifolia.
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 open petals form 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 was introduced to the Wildflower Garden by Eloise Butler in 1912. Additional plants were added in 1915, '18, '26, '27, and '32. In her day she used the now unaccepted name of Steironema quadrifolium. It was not listed on Martha Crone's 1951 census. For an unknown reason it has never been replanted. It 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.
Fourteen species of Lysimachia are of record in Minnesota per the U of M Herbarium as of 2018; several have not been collected in recent decades. Ten are still listed currently by the DNR on their plant surveys. Of those nine are native, one is introduced. The species of Lysimachia of record in the Garden, current and historical, are: Starflower, L. borealis; Fringed Loosestrife, Lysimachia ciliata; Moneywort, L. nummularia (the introduced species); Prairie Loosestrife, Lysimachia quadriflora; Whorled Loosestrife, L. quadrifolia; Swamp Candles, Lysimachia terrestis; Tufted Loosestrife, Lysimachia thyrsiflora; Garden Loosestrife, Lysimachia vulgaris.
Family Change: Some of the leading references have moved the species of Lysimachia from the Primrose (Primulaceae) family into another plant family - Myrsinaceae, following the lead of Flora of North America (FNA) (Ref. #W-7). The U of M Checklist of the Vascular Flora of Minnesota (Ref.#28C) follows this classification. FNA states: “M. Källersjö et al. (2000) and B. Ståhl and A. A. Anderberg (2004) removed the nonrosette terrestrial members from Primulaceae in the broad sense and placed them in the Myrsinaceae, which are further distinguished by leaves and calyx often dotted with yellow or dark streaks, flowers with relatively shorter corolla tubes, seeds immersed in placentae, and wood devoid of rays or with multiseriate only.”
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.
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"