- Name also: Small Nettle, Dwarf Nettle
- Family: Nettle Family – Urticaceae
- Growing form: Annual herb.
- Height: 10–50 cm (4–20 in.). Stem ascending–erect, often branching, 4-edged, with stinging hairs.
- Flower: Staminate and pistillate flowers separate, but on the same plant, flowers very small. Staminate flower: tepals 4, with sepals, hairy, translucent. Stamens 4, filaments curled inwards as buds. Pistillate flower: tepals 4, with sepals, in different-sized pairs, hairy, larger tepals usually with one stinging hair each. A single carpel, stigma brush-like. Inflorescence catkin-like, 1–2 cm (0.4–0.8 in.) long, shorter than leaf-stalks.
- Leaves: Opposite, stalked, stipulate. Blade elliptic–quite round, with wedge-shaped–blunt base, short-tipped, deeply serrated, both sides with few stinging hairs, light green. Blade approx. 1.5 times as long as broad, stalk approx. 2/3 length of blade.
- Fruit: Elliptic–drop-shaped, flat, yellowish brown, achene protected by tepals.
- Habitat: Gardens, yards, planting beds, arable land, fields, cattle yards, chicken yards, rubbish dumps, sea shores. Nitrophile.
- Flowering time: July–September.
Annual nettle is apparently native to the Mediterranean area, but it has spread vigorously, even as far as New Zealand! As an annual plant it depends on seed production to spread. Its small flowers are wind-pollinated, but it is not completely dependent on air currents alone: its stamens are curved inwards in a bunch, and when the flower opens they straighten up quickly and fling the pollen out onto the wind.
Annual nettle likes nitrogen, and in the wild it favours coastal areas where deposits from the sea pile up, and it thrives around cow-sheds and refuse heaps, where there is a lot of rotting organic waste. It was also able to find suitable places to put down its roots in urban areas until well into the 18th century when people rode horses and travelled in horse-drawn carriages, and soldiers too moved around on horseback. Sewerage and cleanliness were not up to today’s standards, so the extra nutrition deposited by draught animals added body to annual nettle’s habitat. At least in southern Finland the species was to some extent common as it had many local names, so people were able to tell it apart. Annual nettle was not used as much in the house as stinging nettle (U. dioica). Young shoots have been used as a vegetable, however, and also dried for cattle fodder and used medicinally.
Now horses have been replaced by cars and old-fashioned spacious wooden housing blocks by concrete. Biological nitrogen is collected in sewerage works, roadsides are cleaned and planting beds are weeded. Annual nettle can be found only rarely and is seldom recognised. Encountering annual nettle is a noticeable event as it stings more powerfully than stinging nettle. It is also shorter than stinging nettle, a brighter green and shiny, and its leaf is blunt-tipped with the stalk about 2/3 the length of blade.