Description:
Wild four o’clock is a perennial herb, sometimes woody at
the base, reaching 3 to 4 feet tall, that reproduces by seed and
by fragmented root pieces. The overall plant shape is bushy, and
the stems are much branched. The stems are glabrous (smooth), often
four-sided, sometimes ridged and reddish. The stem branching is
opposite and the stems are thickened at the nodes. The leaf arrangement
is also opposite. The leaves are usually cordate (heart shaped)
to ovate, sometimes with a truncate base, ranging from 2 to 4 inches
long and 1 to 3 inches wide. The leaves are glabrous, or nearly
so. The leaf margins are entire, and each mid to lower leaf is supported
by a short petiole. The upper leaves may be sessile. The upper stems,
and leaves are sometimes glaucous (covered with a whitish or bluish
waxy covering). The flowers are found in terminal clusters, on forked
branches. A short, hairy stalk supports each cluster of usually
three to five flowers, and an involucre (whorl of bracts) is found
at the base of each flower. This involucre is persistent, 5-lobed,
5-6 mm long at flowering. When in fruit, the involucre increase
to 8-16 mm, becomes veiny and turns colors, and it also aids in
the dispersal of seeds. The flowers are perfect, and consist of
a reddish to lavender calyx (5 sepals), no petals, 3-5 stamens and
a pistil with a single style. The flowers are about 3/8" in
diameter. The seed is a hard, elongated nutlet. It is prominently
five-ribbed, warty, somewhat hairy, grayish brown in color and ranges
from 1/8 to 1⁄4 inch in length. The thick and fleshy, black
taproot is large and tough. The root system can extend downward
for two feet.
- Mechanical:
Hand pulling is not recommended because the stems break at the
crown, the roots are strongly branched, and broken root pieces
will produce sprouting. Small infestations can be spaded, or dug
up. Repeated mowing or cultivation will prevent seed production
to lower the seed bank, and eventually the plant will die from
loss of nutrient reserves stored in the root.
- Biological:
Susceptible to Mirabilis mosaic caulimovirus (Brunt et al. 1996).
- Herbicide:
Wild four o’clock is considered resistant to 2,4-D (Jennings
et al. 1980). Refer to the State
Noxious Weed Control Board site
For More Information:
Detailed information about Wild
Four O'Clock is available at the Washington State Noxious Weed
Control Board Web Site. |
