Sensitive Briar

The genus name Mimosa is Greek in origin and means “mimic”. Quadrivalvis probably refers to the four parts of the mature seed pod. Nuttallii is the varietal name and honors Thomas Nuttall, the English botanist who studied plant life in the US in the 1800’s.

The common name “Sensitive briar” was given because the leaves fold up when touched or otherwise disturbed. I've seen it spelled 'briar' and 'brier' and it seems either one can be correct. Additional common names include Devil’s shoestrings and Cat’s claw or Catclaw brier, both probably referring to the recurved prickles on the stem. Mimosa quadrivalvis var. nuttallii is a perennial in the Bean (Fabaceae) family.

The flowers of Mimosa quadrivalvis definitely have a "wow" factor. The flower heads arise on long stalks at the leaf axils. Each globe shaped flower head is actually composed of multiple flowers, which are hidden inside and not visible without dissecting the flower head. The visible parts of the flowers are the hot pink filaments topped with prominent yellow anthers. The internal flowers of each flower head all open at once to create the pompon. The flashy flower heads remind me of fireworks.

Sensitive briar grows from a deep tap root. It's a creeping plant with a length of 4 to 5 feet that tends to crawl along the ground, or upon surrounding vegetation. Mature plants have multiple stems. The stem is variably green or pink and covered with recurved prickles.

The alternate leaves are bipinnately (twice pinnate) compound. This means that each leaf is divided into primary leaflets that further divide into secondary leaflets.

The leaves of Sensitive briar respond to various stimuli by folding along the primary leaflet. You can initiate this reaction simply by touching a leaf with your finger, a twig or any handy object. The folding may also occur due to wind or darkness. The leaves fold up each night. This reaction is termed seismonasty and is quite common in the Mimosaceae family.

Before flowering, the buds somewhat resemble green bramble fruits such as blackberry. When flowering is complete in mid summer, the interesting seed pods appear. Each slender pod is covered with prickles. The pods curve and often form interesting shapes. Once the seeds are ripe and the pods are dry, they spit and reveal their dark brown seeds.

The main pollinators of Sensitive briar are various types of bees. I've documented several types of Sweat bees, Bumble bees such as the Brown-belted Bumble bee and American Bumble bee as well and Large Carpenter bees. Since the plant doesn't produce nectar, the bees are seeking pollen. I've also seen various Syrphid flies who are known to be important pollinators of many plants.

Blister beetles such as the one below visit flowers to feed on the pollen. They are probably not very effective pollinators but many beetle species are known as important pollinators, so perhaps.

Many other interesting insects visit the plants either to consume the foliage, hunt other insects or perhaps just to chill out.

Grasslands and dry, rocky glades are preferred habitat for Sensitive briar. It is also seen growing at woodland margins.

The variety nuttallii is sometimes treated at the species level and sometimes as a varietal level. It seems there isn't a definitive answer as to what is correct at this time. Mimosa quadrivalvis var. nuttallii is native to the central part of the US, from South Dakota to Colorado and down to Texas and Louisiana and back up to Iowa and Illinois. Natureserve shows it as Critically Imperiled in Colorado, Iowa and Illinois. It's Secure in Kansas and other states show No Status Rank.

Sensitive briar provides forage for deer and turkey. Bobwhite quail consume the seeds and the nectar is important for many insects. It is also nutritious for livestock. How they eat the briers, I surely don’t know! Nevertheless, its absence in a field is said to be a good indicator of overgrazing. The flowers are very attractive to birds, bees and other insects.