BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Lepidium latifolium | Perennial Pepperweed 



GENERAL BOTANICAL CHARACTERISTICS : 
Perennial pepperweed is a perennial herb that forms dense colonies by
adventitious shoots from roots and deep-seated rhizomes [9,12,14,15,25].
It grows from 1.6 to 6.6 feet (0.5-2 m) tall [8,11,14,15].  Leaves are 4
to 12 inches (10-30 cm) long and 2 to 3.2 inches (5-8 cm) wide
[8,9,10,11,17].  The fruit is a silicle 0.08 to 0.1 inch (2-2.5 mm)
long, with two seeds [4,10,27].  Perennial pepperweed has an extensive
root system [10,12,15].



RAUNKIAER LIFE FORM : 
   Hemicryptophyte
   Geophyte


REGENERATION PROCESSES : 
Vegetative:  Perennial pepperweed spreads vigorously by sprouting from
roots and rhizomes [14,15,17].  Plants reproduce mainly by rhizomes
[25], but can be aggressive colonizers of disturbed areas [14].  

Sexual:  Perennial pepperweed reproduces by seed.  It produces abundant
highly germinable seeds [15].  Seeds are wingless; thus wind dispersal
is negligible [8,17].  Perennial pepperweed seeds have high rates of
germination, often with widely fluctuating diurnal temperature regimes.
Seeds were collected from a perennial pepperweed infestation growing in
a swampy meadow at Reno, Nevada, and from two locations along the Susan
River in California.  A total of 55 constant- and
alternating-temperature regimes were used to test germination of
perennial pepperweed seeds.  No significant (P=0.01) differences in the
overall mean germination of seeds were observed between the Reno samples
(1982 and 1983) and the Susan River samples (1983).  Also, no
significant (P=0.01) differences in mean germination of perennial
pepperweed seeds tested 1, 6, and 12 months after harvest were observed;
thus, seeds can be stored for at least 1 year.  The three alternating
temperature regimes that produced optimum germination for pooled
populations of perennial pepperweed seeds were 41/95, 50/104, and 59/104
degrees Fahrenheit (5/35, 10/40, and 15/40 deg C, respectively), with
germination rates of 92, 96, and 93 percent, respectively.  These
temperature regimes probably occur naturally for seeds not deeply
buried.  Seeds apparently have no inherent dormancy [15].


SITE CHARACTERISTICS : 
Perennial pepperweed is common in fields, waste places, meadows, borrow
ditches, and along roadsides [9,10,14,26,27].  It also invades irrigated
pastures, cropland, and native meadows [15].  It is most often found in
open, unshaded areas on disturbed, and often saline soils [3,4,11,28].
It is locally common in riparian areas, marshy floodplains, valley
bottoms, and seasonally wet areas [2,15,26,28].  

Perennial pepperweed is found from 5,500 to 8,000 feet (1,650-2,400 m)
in Colorado, 4,125 to 9,042 feet (1,250-2,740 m) in Oregon, 4,125 to
7,953 feet (1,250-2,410 m) in Utah, and at less than 6,270 feet (1900 m)
in California [10,11,26,28].  


SUCCESSIONAL STATUS : 
Facultative Seral Species

Perennial pepperweed is an aggressive colonizer of riparian habitats.
It establishes rapidly and can eliminate competing vegetation.
Infestations of riparian areas provide ready sources of seed for
invasion of adjacent meadows, irrigated pastures, croplands, and river
systems [14,25].  Perennial pepperweed is not aggressive in its native
habitat, possibly because of natural predation [14].  


SEASONAL DEVELOPMENT : 
Perennial pepperweed flowering dates for several states are as follows:

California         June-Aug     [17]
Colorado           June-Aug     [9]
Connecticut        Aug          [20]
Massachusetts      Aug          [20]
Nebraska           June-Aug     [9]
Oregon             June-Aug     [27]

Related categories for Species: Lepidium latifolium | Perennial Pepperweed