Desmodium nudiflorum (Naked-flower Tick-trefoil)
|Also known as:||Stemless Tick-trefoil, Naked-stem Tick-trefoil|
|Habitat:||part shade, shade; rich woods|
|Bloom season:||July - August|
|Plant height:||12 to 40 inches|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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One or more clusters of stalked flowers at the top of a naked stem, with the flowers in pairs and loosely arranged on the stem. Flowers are ¼ to 1/3 inch long with a rounded upper petal and 3 narrower lower petals that are longer than the upper. The stamens and pistil form a curving tube that protrudes from the center, between the lateral petals. Flower color is pink to violet, occasionally white.
The calyx behind the flower is sparsely minutely hairy, pale greenish-white with red spots or streaks at the base, bell-shaped with 4 short lobes, the lowest lobe largest and pointed at the tip. Flower stalks are slender, up to about ¾ inch (1 to 2 cm) long at maturity, typically red and minutely hairy.
Leaves and stems:
Leaves are compound in 3s, alternately attached on the stem but crowded and appearing whorled. Leaflets are 1½ to 4 inches long, up to 3 inches wide, toothless, hairless to sparsely hairy, lance-oval to egg-shaped with a rounded to wedge-shaped base and a pointed tip. The terminal leaf is largest and broader than the lateral leaflets, but always longer than wide. The compound leaf stalk is 2 to 3 inches long, hairless to sparsely hairy.
The flowering stem and and leafy, vegetative stems are forked from the base, the flowering stem typically running a short distance underground before rising up. The flowering stem is usually leafless, rarely with 1 or more leaves below the flower cluster. Stems are erect to ascending, unbranched, and minutely hairy, the flowering stem up to 40 inches tall and the vegetative stem up to about 12 inches.
Fruit is a flat pod divided into 1 to 4 segments, each straight to slightly concave on the upper edge and somewhat triangular on the lower, and each containing a single seed. The pod is covered in minute hooked hairs so it sticks to almost anything that passes by.
Naked-flower Tick-trefoil is very rare in Minnesota, where it reaches the northwest edge of its range. First recorded from Chisago County in 1892, it wasn't documented in the state again until nearly 100 years later. According to the DNR, in Minnesota nearly 90% of the mesic forest where this species lives has been degraded or destroyed by logging, agriculture and development, with additional threats from invasive species such as buckthorn, exotic honeysuckles, and garlic mustard. D. nudiflorum was listed as a Special Concern species in 1996 when 15 total populations were known, but elevated to Threatened in 2013 after biological surveys only found 2 additional populations. It is not a very competitive species and all populations are small.
Naked-flower Tick-trefoil is not easily confused with other species, distinguished by the (usually) leafless flowering stem, separate stem of compound leaves with mostly hairless leaflets, loosely arranged raceme with flower stalks becoming 1 to 2 cm long, and pod segments somewhat triangular in shape. It is a smaller, more delicate plant than the common Pointed-leaf Tick-trefoil (Desmodium glutinosum or Hylodesmum glutinosum), which has all its leaves on the flowering stem, leaflets are proportionately broader and more sharply pointed, and the flower stalks are less than 1 cm long. Several references have renamed D. nudiflorum to Hylodesmum nudiflorum; this name is not currently recognized in Minnesota but may be in the future.
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- Naked-flower Tick-trefoil plant
- Naked-flower Tick-trefoil plant
- vegetative stems
- leaf scan
- close-up of flower
Photos by K. Chayka and Peter M. Dziuk taken in Wisconsin.
Have you seen this plant in Minnesota, or have any other comments about it?