or Tall whitetop or Perennial pepperweed [Lepidium
latifolium L.][LEPLA][CalEPPC: A1][CDFA list: B] Photographs
Map of Distribution
perennial peppergrass or peppercress,
slender perennial peppercress, broadleaved or broadleaf pepperweed,
tall whitetop, giant white weed, iron weed, Cardaria latifolia
DESCRIPTION: Erect noxious perennial to 2 m tall,
with white flowers and extensively creeping roots. Plants
are highly competitive and typically form dense colonies
that displace native vegetation and wildlife. Toxicity to grazing
livestock is undocumented. Goats appear to tolerate heavy consumption
of fresh plants. However, there have been reports of horses becoming
ill after being fed contaminated hay. Perennial pepperweed
has spread rapidly throughout the western U.S. since its introduction
from Eurasia around 1936. Outside of California, it is a major
problem in Nevada.
obovate to oblong, ~ 3-8 mm long, glabrous, tip rounded, base
tapered into a short stalk ~ 2-3 mm long. First leaves developmentally
alternate, but appear opposite, ovate to oblong, ~ 4-12 mm long,
glabrous, tip +/- rounded, base +/- wedge-shaped, on a stalk ~
5 mm long. Margins entire to slightly wavy. Subsequent leaves
resemble first leaves and are increasingly larger.
Crown and lower stems +/- weakly woody. Foliage glabrous,
green to gray-green. Leaves alternate, lanceolate to elliptic
or oblong. Basal leaves to 30 cm long and 8 cm wide, with serrate
margins and on long stalks (~ 3-15 cm long). Stem leaves reduced,
+/- sessile, tapered at the base, margins entire
to weakly serrate.
and UNDERGROUND STRUCTURES: Roots long, thick, minimally branched, vigorously
creeping. Most roots occur in the top 60 cm of soil, but some
can penetrate to depths of 3 m (10 ft) or more. Carbohydrate reserves
are lowest when flowering stems are elongating (bolting stage).
back to top of page
Inflorescences +/- pyramidal to rounded on top. Petals
4, white, spoon-shaped, ~ 1.5 mm long. Sepals oval, less than
1 mm long, +/- covered with long simple hairs. Stamens 6, 4 long,
2 short. Insect-pollinated.
and SEEDS: Pods (silicles) 2-chambered, round to slightly
ovate, slightly flattened, lacking a notch at the apex,
~ 2 mm long, +/- covered with long simple hairs. Stigma
sessile, persistent. Stalks much longer than pods, glabrous
or sparsely pubescent. Seeds ellipsoid, slightly flattened, +/-
1 mm long, 0.5 mm wide, reddish-brown, with a shallow groove on
each side and minutely granular surface. Seeds fall from pods
irregularly through winter and some may remain in pods until the
CHARACTERISTICS: Above ground parts typically die in late fall and
winter. The pale tan dead stems persist for more than one year.
riparian areas, meadows, salt marshes, flood plains, beaches,
roadsides, irrigation ditches, agronomic crops, especially alfalfa,
orchards, vineyards, irrigated pastures, ornamental plantings.
Typically grows on moist or seasonally wet sites. Tolerates saline
and alkaline conditions.
California, except deserts and northern North Coast and adjacent
mountains (Del Norte, Humboldt, n Mendocino cos.); to Canada,
Montana, Indiana, Texas. Also, regions of the Northeastern U.S.
To ~ 2000 m (6500 ft).
vegetatively from creeping roots and root fragments
and by seed. Roots do not hold soil together very well,
allowing erosion of river, stream, or ditch banks.Root fragments
and seeds float and disperse with flooding, soil movement, and
agricultural and other human activities. Seeds can also cling
to tires, shoes, and the feet, fur, and feathers of animals and
contaminate hay or crop and pasture seed. Large fragments can
survive extreme desiccation on the soil surface for extended periods.
Fragments as small as 1-2 cm long and 2-8 mm in diameter can develop
into new plants. New shoots begin to grow from roots in late winter.
Fluctuating temperatures appear to stimulate seed germination.
Plants usually produce abundant, often highly viable seed, but
seedlings are seldom detected in the field. In wet years, seed
production is sometimes limited by white rust (Albugo sp.)
infection. Seedlings emerge mid-winter through mid-spring.
FAVORING/DISCOURAGING SURVIVAL: Heavy infestations are difficult to control. Cleaning
agricultural or earth-moving machinery after use in infested areas
and curtailing movement or use of soil, hay, and crop or pasture
seed contaminated with perennial pepperweed root fragments
and/or seed and can help prevent new infestations. Single techniques,
such as repeated mowing, hand-digging, cultivation, grazing, and
burning, typically do not adequately control perennial pepperweed.
In addition, cultivation may increase infestations by dispersing
root fragments. Field observations suggest that plants may not
tolerate an extended period of flooding during the growing season.
Hoary cress [Cardaria draba (L.) Desv.], lens-podded whitetop
[Cardaria chalepensis (L.) Hand.-Mazz.], and hairy whitetop
[Cardaria pubescens (C. Meyer) Jarmol.] are noxious perennials
with creeping roots that resemble perennial pepperweed. Field
pepperweed [Lepidium campestre (L.) R.Br.] and clasping pepperweed
[Lepidium perfoliatum L.] are related annual/biennials. Unlike
perennial pepperweed, all of these species grow only to ~ 0.5 m tall
and have stem leaves with lobed bases that clasp the stems and foliage
+/- covered with short hairs. In addition, Cardaria species typically
have inflated pods greater than 2 mm long with persistent styles 1-2
mm long. Field pepperweed and clasping pepperweed do not grow
in dense colonies.
An excellent summary of biology, ecology and control information
for perennial pepperweed (Leaflet #02-1; January 2002) has been produced by
Mark Renz, Carl Bell, Cheryl Wilen, and Joseph M. DiTomaso through the University
of California Cooperative Extension. The information can be accessed via the
world wide web at the following address: http://wric.ucdavis.edu/information/pepperweed.html
back to top of page