Stinging nettle is a perennial that spreads by rhizome and seed. It is an infamous native of the Pacific Northwest.
It gets its name from the myriad of spines that cover foliage and stems. These small hollow spines pierce human skin and inject small amounts of formic acid. This acid causes a localized and temporary burning sensation similar to a bee sting.
Urtica is derived from the root 'uro', which means to burn. Dioica gives reference to the fact that flowers on these plants are diecious, that is, male and female flowers occur on separate plants.
Stinging nettle is a common weed of drainage ditches, fence rows, disturbed sites, and wooded recreational areas. It rarely occurs in maintained agricultural fields. Because it 'stings' those who make contact, it most problematic in recreational areas where children and unsuspecting adults frequent.
Its habit is upright and columnar, often growing in small colonies (because it is rhizomatous).
Foliage is oppositely arranged along the stem. Foliage is dentate and lanceolate.
Leaves are covered with spines on the upper and lower surfaces.
Stems are square and covered with spines. Also note in the image below the 4 stipules that occur at the base of each petiole. Stipules are, generically speaking, leaf-like structures that occur at the base of petioles.
These stipules are somewhat unique, and are the first thing I look for when I see a plant I suspect to be stinging nettle.
Flowers occur in axillary or terminal clusters called panicles.
There are many individual flowers in each cluster.
In the image below, yellow-white flowers emerge from purple-colored sepals.
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