Heartleaf 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/deltate shaped with heart shaped bases and have stalks of up to 1 inch long on the lower leaves, shorter on the upper. Leaf size reduces abruptly 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. Involucral bracts form a pedunculate (5-parted), somewhat star-shaped cup which subtends a cluster of flowers, usually 3 flowers, but there may be just 1 or 2, or even 5. This is an interesting arrangement found in the Nyctaginaceae family.
Flowers are tubular, with a saucer shape opening, positioned above the star shaped cup of the involucral bracts. There are no petals, instead the flower calyx has showy pigmented lobes (sepals) 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. After flower fertilization the green involucral cup 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. Seeds need no treatment if sowed fresh in a warm environment; if stored they should be keep cold and dry.
Habitat: Heartleaf Four-o'clock 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, which was the name originally assigned in 1803 by Michaux. 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. Two important works of his are the Histoire des chênes de l'Amérique septentrionale (1801 - Oaks of North America), and the Flora Boreali-Americana (2 vols., 1803, published posthumously, and containing the description of this plant). His son Francois, traveled with him and the father’s notes were later used for the 3-volume North American Sylva. Michaux's work was updated in 1892 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 other two species have leaves that are not are triangular like 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 cup formed by the involucral bracts 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 involucral 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 involucral cup 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 Heartleaf Four-o'clock in June 1910 with plants obtained in Minneapolis at Clinton Ave and 27th St.; on Aug. 8, 1912 with plants from Glenwood Springs (an area next door to the Garden) and again in 1922. Martha Crone noted planting seeds in 1944 and 12 plants in 1945 using the name Allionia nyctaginea which is how she listed it on her 1951 inventory of plants in the Garden at that time.
Heartleaf 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.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"