Wild four-o'clock (Mirabilis nyctaginea) is an increasingly common native plant that can be considered both a weed and a wildflower, depending on the setting. It is widely distributed throughout the Great Plains and has spread eastward to the coast. It is a perennial plant, which is a desirable characteristic as a wildflower but a less than desirable characteristic as a weed.
The plant has a smooth, nearly square stem that can grow 2 ½ ft. tall. The leaves that arise opposite on the stem are heart shaped and up to 3 inches in length, resembling a large lilac leaf. The heart shape of the leaf gives rise to a second name by which the plant is known - heartleaf four o'clock. The root system consists of a stout, fleshy taproot that reaches deep into the soil.
Flowers arise at the end of the stem, clustered in a terminal panicle. The flowers have no true petals. Instead, the sepals are fused together into a trumpet shape. Flower color ranges from pink to reddish purple and, on rare occasion, white. The bloom period is rather long, stretching from May through September. Each flower cluster produces several seeds. As the name suggests, the flowers open later in the afternoon. They remain open through the night and close the following morning.
The majority of pollination takes place during the night through the activity of nocturnal insects. Honey bees also play a pollination role during the daytime, visiting the flowers early in the morning before they close and later in the afternoon after opening. Wild four-o'clocks are also self-pollinating, so pollination of the flowers and seed development is assured.
Wild four-o'clocks can be found in quite varied habitats. It thrives in a wide range of soil types including very poor soil conditions. It can be found in both urban and rural settings. In conservation and no-till production systems, wild four-o'clocks can become a real problem. Heavily grazed pastures are another favored habitat because of the reduced competition from the grazed grasses; wild four-o'clocks move into that niche and become establishe. Other areas that this plant can be found include roadsides, fence lines, railroad rights-of-way, and waste areas that have been neglected over time.
Wild four-o'clocks are propagated both by seed and less commonly through vegetative reproduction. The seeds drop near the parent plant and germinate. The seeds have a high viability rate and dense areas of wild four-o'clocks can become established. Vegetative reproduction can occur when pieces of the taproot sprout and grow, although this is less common than seed propagation.