Resource Library
Plant of the Week: Four O'Clock
The University of Arkansas System Division of Agriculture does not promote, support or recommend plants featured in "Plant of the Week." Please consult your local Extension office for plants suitable for your region.
Plant of the Week
Four O'Clock
Latin: Mirabilis jalapa
In this busy world we live in, sometimes what we think we see and know is but a caricature
of reality. The lowly four o’clock, a common flower of our great-grandmother’s garden,
is a plant that looks like your typical plant, but in reality is anything but typical.
Four o’clock is a tender perennial that grows from 18 to 30 inches tall with stout
stems and an abundance of late summer flowers that open about four o’clock in the
evening, after the heat of the day is past.
The flowers are not responding to an internal clock but to temperature. The flowers
are responding to the patterns of a moth that avoids the heat of the day to make its
daily rounds. Usually, the flowers close the following morning, but if the day is
cool, they will stay open until the new flowers open.
Four o’clock flowers are trumpet-shaped, with the throat as much as 2 inches long
and 1 inch wide with five lobes. Flowers are produced in shades of white, yellow and
about every shade of pink imaginable. The striped flowers appear to be infected with
a virus disease that creates the interesting patterns.
The flower is an enigma in that the four o’clock completely lacks petals. The showy
portion of the flower is actually an outgrowth of the sepal, which in most plants
is green and leaf-like. The small leafy structure from which the flower emerges is
made of bracts formed from modified leaves. While the absence of petals is rare in
the plant kingdom, it is a common characteristic of the family Nyctaginaceae to which
four o’clock belongs.
Each flower that is pollinated produces a pea-size black "seed." But, again the seed
is not really a seed but a fruit. A true seed is produced inside something -- for
example, inside a pea pod or the capsule of a petunia. In this case, each flower produces
one seed that is enclosed inside the ovary. So, in reality the "seed" is a "fruit."
Even the name of the plant is a misnomer. The name Mirabilis was given by Linnaeus in the middle 18th Century and shortened from the Latin word
"Admirabilis" which gives us "admirable" and is a reference to the showy flowers.
The name "jalapa" is due to botanical confusion. The fleshy roots of this plant were
thought to be the source of "jalapa," a drug that was used in Central and South America
as a laxative. In reality, the jalapa was from a member of the morning glory family.
Four o’clock is one of our oldest garden flowers and was originally shipped back
to Europe by the Spanish conquistadors. It does well in sunny, warm sites throughout
the state. It forms dahlia-like tubers that will usually live through the winter and
permit the plant to come back from the roots. It will also reseed in an area but is
not really broad spreading.
The flowers are fragrant and produce a subtle and delightful fragrance during the
early evening hours when the wind is not blowing. Hummingbirds and lunar moths both
seem to like to visit the flower for the abundance of nectar. The stems and roots
can cause serious stomach upset if consumed and some people have experienced dermatitis
from handling the tuberous roots.
By: Gerald Klingaman, retired
Extension Horticulturist - Ornamentals
Extension News - October 8, 1999
The University of Arkansas System Division of Agriculture does not maintain lists of retail outlets where these plants can be purchased. Please check your local nursery or other retail outlets to ask about the availability of these plants for your growing area.