Northern Prairie Wildlife Research Center
Water Loosestrife (Lysimachia thyrsiflora)
- Family: Primrose (Primulaceae)
- Flowering: May-July.
- Field Marks: This loosestrife lacks cilia near the base of the leaves. There are small leaves at the base of the normal leaves. The flowers and fruits are borne in short clusters.
- Habitat: Swamps, wet prairies.
- Habit: Perennial herb with slender rootstocks.
- Stems: Erect, usually unbranched, smooth, up to 2 feet tall.
- Leaves: Opposite, simple, elliptic to lanceolate, pointed at the tip, tapering to the base, without teeth, smooth, up to 4 inches long, less than 1 inch broad.
- Flowers: Several in small, axillary, spike-like clusters up to 1 1/2 inches long; each flower yellow, to 1/4 inch across.
- Sepals: 6, green, very narrow, united at the base.
- Petals: 6, yellow, black-spotted, very narrow, united only at the base, up to 1/4 inch long.
- Stamens: 6.
- Pistils: Ovary superior.
- Fruits: Capsules spherical, black-dotted, up to 1/4 inch in diameter.
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