Species of the Week: Ponted-Leaf Tick Trefoil

Species of the Week
Number 8 -- July 24, 2006

In the Species of the Week feature of the Wildwood Web we took a close look at one of the species that lives in Wildwood. To see the earlier featured species check the Species of the Week archives.

Pointed-Leaf Tick Trefoil

Desmodium glutinosum

Most of our Species of the Week have been showy plants of disturbed areas, such as along the bikeway and Wildwood Drive. This week's plant is showy, but it hides in rich woods. Look for it along the trails on the west side of the park, towards the north, in the area near Adam's Cave.

Pointed-Leaf Tick Trefoil has tiny, irregular pink flowers, arranged on a long stalk. The leaves are divided into three segments (trefoil comes from an old French word for "three leaves"). The middle leaflet is abruptly pointed, hence the common name. The fruits are similar to flat pea pods, except that they are constricted between the seeds to form a jointed fruit. This unusual fruit is called a loment by botanists.

This plant is in the Fabaceae or bean family. Peas and beans are familiar cultivated members of the family. Many alien weeds in Wildwood belong to this family, clovers, wild sweet pea, and sweet clover. Tick trefoils, however, are native. Members of the bean family have unusual flowers and pointed-leaf tick trefoil is very typical. There are five petals. One is larger than the others and is held at the top of the flower; this is called the standard. Two lower petals are fused together for part of their length and form a little pouch holding the sexual parts of the flowers; together these are called the keel. The remaining two petals flank the keel to either side; these are the wings. All of these parts are clearly visible in the picture at right.

Pointed-leaf tick trefoil is found in rich woods from Nova Scotia to Saskatchewan, south to Georgia and Texas.

The genus name, Desmodium, comes from the Greek desmos meaning connected, and presumably referring to the fruits. The species name, glutinosum, means glutinous or sticky and refers to the sticky leaf stalks.

GGC