Heart-leaved Four-o'clock is a native erect perennial forb growing on stems that are 1 to 3 feet high and usually smooth and slightly angled. It branches occasionally.
Leaves are opposite, entire (no teeth), oval shaped that have heart shaped bases and have stalks of up to 1 inch on the lower leaves, shorter on the upper. Leaf size reduces abruply in the inflorescence. Leaves are held in an ascending position and usually have smooth surfaces.
The inflorescence is a forked stalked cluster of flowers that is atop the stem and sometimes with axillary clusters rising from the upper leaf axils. There are pairs of small leaves (bracts) at the base of the inflorescence. The buds and flower stalks (pedicels) may have fine hair, sometimes glandular. The involucre is pedunculate (5-parted), somewhat star-shaped, and usually subtends 3 flowers, but there may be just 1 or 2, or even 5.
Flowers are tubular, with a saucer shape opening, positioned above the star shaped cup of the involucre. There are no petals, instead the flower perianth has pigmented lobes replacing the corolla; these lobes may be pink to purple, and rarely, white. The flower is bisexual with from 3 to 6 stamens with magenta filaments and yellow anthers and the ovary has one style with a blunt stigma. Both stamens and style are exserted with the styles exserted beyond the stamens. The cup-like green involucre (bract) after flower fertilization enlarges greatly during seed production and acts like a parachute for the distribution of the seed.
Seed: The seed is a small, hard, cylinder shaped nutlet, tapered at both ends with longitudinal ribs that have fine hair. It is dark grayish brown to reddish brown.
Habitat: The plant is perennial, growing from a deep tap root. It likes full sun in drier prairie type soil. It will self-seed and become weedy in disturbed areas.
Names: Flowers open in late afternoon and remain open at night, hence the name Four-o'clock and this also gives the species name nyctaginea, which is Greek for night blooming. The plant has undergone several botanical classifications over the years. In Eloise Butler's time the name used was Oxybaphus nyctagineus; In Martha Crone's era the name used was Allionia nyctaginea. It is now in the genus Mirabilis, Latin for 'miraculous' or 'wonderful'. The author names for the plant classification are: First to classify was - (Michx) which refers to Andre Michaux (1746-1802), French botanist who made many exploring expeditions in the U.S. collecting and cataloguing many species. His notes were later used by his son, Francois, who with Thomas Nuttall published the multi-volume North American Sylva. Michaux's work was updated by ‘MacMill.’ who is Conway MacMillan (1867-1929), American botanist, Professor of Botany, University of Minnesota, author of Minnesota Plant Life (1899) and other publications.
Comparisons: M. nyctaginea is one of three species of the genus found in Minnesota, the other two being M. albida, White Four-o'clock and M. linearis, Narrow-leaf Four-o'clock. These three are the only members of the Nyctaginaceae family in Minnesota. The other two species have leaves that are not are triangular of M. nyctaginea. There are also differences in the seed. Flora of North America (Ref. #W7) has a good key to distinguish the species.
Above: 1st photo - The bract like cup (the involucre) initially is green and encloses 1 to 5 flower buds. It unfolds for the flowers to rise above the cup and open. After flowering the cup enlarges. 2nd photo - Distinctive Leaves, with heart-shape bases. 3rd photo - The enlarged involucre cup 2 weeks after flowering. Note the pale green bracts a the base of the cluster.
Below: The seed is a small, hard, cylinder shaped nutlet, tapered at both ends with longitudinal ribs that have fine hair. The dry lobes of the involucre act like a parachute for the distribution of the seed. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Below: Leaf detail. 1st photo - The heart-shaped bases terminate in a short stalk. 2nd photo - Note the small pale green pair of bracts at the base of a flower cluster that has risen from the axils of there two leaves.
Notes: Eloise Butler planted Heart-leaved Four-o'clock in June 1910 with plants obtained in Minneapolis at Clinton Ave and 27th St. and again on Aug. 8, 1912 with plants from Glenwood Springs (an area next door to the Garden). Martha Crone noted planting seeds in 1944 and 12 plants in 1945 using the name Allionia nyctaginea.. This plant was listed on Martha Crone's 1951 inventory of plants in the Garden at that time.
Heart-leaved Four-o'clock is native to Minnesota except for a few scattered counties, most of which are in the far north of the state. It is found throughout North America except the far north, the Canadian maritime provinces and several U.S. states in the far south. There are 21 species of Mirabilis in North America.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"