Tick Trefoils (Sticktights; Beggar's Lice)

Desmodium spp. (17 species in Missouri)

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Photo of tick trefoil plant with flowers
Missouri has 17 species of tick trefoils, which live in a variety of habitats. Hikers know them well from their chains of hairy little seedpods that stick to clothing like parasites!
Jim Rathert
Other Common Name
Beggar Ticks; Tick Clover; Tick-Trefoil
Family

Fabaceae (beans)

Description

Missouri has 17 species of tick trefoils. Species identification is difficult and often depends on close analysis of the seedpods. The plants in this genus vary, with habits ranging from prostrate (lying on the ground) to erect stems. Flowers are usually in terminal racemes; pink, violet, or white; having the characteristic form of pea flowers. Blooming period is July–September, varying depending on species. Leaves are alternate, 3-divided, varying in shape and length of petiole, the lateral (side) leaflets usually on very short stems with the center leaflet on a longer stem. Fruit in distinct papery pods, which break up into 1-seeded segments that are dispersed by animals, including people.

Similar species: Three species that used to be in genus Desmodium are now placed in the genus Hylodesmum; they are different from desmodiums in several details of flower and fruits. For example, their fruits narrow markedly at their base, forming a stalklike shape, and the constrictions between the segments of the fruit are deep and very unsymmetrical. Despite their new genus name, they are still commonly called tick trefoils and sticktights.

Size

Height: to 3 feet or taller.

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Photo of tick trefoil sticktights on denim fabric
Tick Trefoil (Beggar’s Lice; Beggar’s Ticks; Sticktights)
The fruits of tick trefoil plants are basically flattened bean pods that, instead of splitting lengthwise, split crosswise, with one bean (seed) for each triangular section.

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Photo of tick trefoil flowers at Tucker Prairie
Tick Trefoil at Tucker Prairie
Tick trefoil flowers have the familiar shape of all pea-family flowers.

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Photo of a tick trefoil leaf
Tick Trefoil Leaf
Tick trefoils have compound leaves with three leaflets, thus the name "trefoil."

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Photo of tick trefoil flowers with foliage in the background
Tick Trefoil Flowers
Tick trefoils live in a variety of habitats. This one was growing in an upland forest in the Ozarks.

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Photo of a tick trefoil plant growing in an upland forest
Tick Trefoil at Spring Creek Gap CA
Tick trefoils have a variety of growth forms, based on species but also on habitat.

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Photo of tick trefoil leaves
Tick Trefoil Leaves
Like all tick trefoils, this plant has trifoliate (three-compound) leaves. Note how the central leaflet has a longer stalk than the two side leaflets.

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Photo of sessile-leaved tick trefoil flower stalks with prairie grass and sky in background
Sessile-Leaved Tick Trefoil
This might be Desmodium sessilifolium, sessile-leaved tick trefoil. It is common on prairies.

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Photo of a sessile-leaved tick trefoil flower
Sessile-Leaved Tick Trefoil Flower
The flowers of sessile-leaved tick trefoil usually are white when they first open.

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Photo of flower stalks of sessile-leaved tick trefoil, held on fingers for scale
Sessile-Leaved Tick Trefoil
As the flowers of sessile-leaved tick trefoil mature and age, they turn from white to yellow.

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Photo of sessile-leaved tick trefoil leaves
Sessile-Leaved Tick Trefoil Leaves
Here is what sessile-leaved tick trefoil is named for: note how short the leaf stalks are.

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Photo of sessile-leaved tick trefoil fruits on stalk, cradled on a hand.
Sessile-Leaved Tick Trefoil Fruits
Identifying tick trefoils to species usually requires noticing details of fruit, flowers, leaflet shape, and so on.

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Photo of a tick trefoil flower stalk with prairie and sky in background
Tick Trefoil at Hi Lonesome Prairie CA
Unknown species of tick trefoil. Most people are doing well if they can identify these plants to genus.

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Photo of tick trefoil fruits and foliage
Tick Trefoil Fruits and Foliage
Unidentified tick trefoil. Note how the fruits are fairly straight and usually have 3 or 4 segments, which are bluntly angled, almost pointed, on the lower edge.

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Photo of tick trefoil leaves
Tick Trefoil Leaves
Identifying tick trefoils requires noting leaf characters. For example, the 2 side leaves here are nearly triangular and lack stalks.
Habitat and conservation

Tick trefoils occur in variable locations, in open and forested places, depending on the species. The interesting fruits of tick trefoils are an example of a common “alternative” form of a bean-family pod: Although we’re all familiar with the “legume” form, like green beans, which split lengthwise into two long halves, tick trefoils have a bean-family fruit type called a “loment.” It's like a flattened chain of beads, splitting crosswise into multiple short, one-seeded segments.

image of Tick Trefoil Beggar’s Lice Beggar’s Ticks distribution map
Distribution in Missouri

Each species has its own distributional range, though the genus is represented statewide.

Human connections

The flattened, hairy pods stick to clothing and animal fur, hence the names “beggar’s lice” and “tick trefoil.” (“Trefoil” means “three-leaved.”) Some desmodiums are used in agriculture to repel insect pests, inhibit the growth of weeds, enrich the soil, and create fodder for livestock.

Ecosystem connections

The plants of this genus are important browse for deer; the seeds are sustenance for many birds. The “sticky” fruits are an adaptation that widens the distribution of seeds from the parent plant: The seeds can be carried as far as an animal might carry them in its fur. This reduces inbreeding and increases the chance that at least some of the seeds will end up in a suitable habitat.