Heart-Leaf Nettle (Urtica chamaedryoides) is a winter annual that we have been seeing here at the Lawn and Garden Help Desk recently. This Florida native plant is commonly found in disturbed areas and even in pastures, where it can be problematic for livestock. But more importantly here in Pinellas County, is that it is commonly found in yards and can be problematic for unprepared gardeners. These herbaceous plants grow in an erect form but are often weak and find support from other plants. The leaves of this plant are triangular in shape and closely resemble the leaves of a strawberry plant, although the overall shape of the plant is very different. Leaves are between .5"-2.5" long and .5"-1.5" wide and are oppositely arranged on the stem.
The cause for concern comes from the fine little hairs found on the stem and leaves of the plant:
Each hair is a brittle tube filled with irritating compounds (histamines and acetocholines). When you brush up against one of these hairs it breaks open and injects these materials into your skin. Intense itching and reddening of the skin are the most common reactions, but some people may experience swelling and burning as well.
This is why it would be good to know this plant before you reach down and try to pull it out. According to the University of Florida fact sheet on Heart-Leaf Nettle, washing the affected area or applying a baking soda paste soothes the stinging sensation. My recommendation is watching out for this stinging nettle and wearing heavy-duty gloves to protect your skin!