BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Lythrum salicaria | Purple Loosestrife 



GENERAL BOTANICAL CHARACTERISTICS : 
Purple loosestrife is a robust, erect, perennial herb with 30 to 50
stems arising from a common rootstock.  Each stem is 4.9 to 6.6 feet
(1.5-2.0 m) tall.  The large rootstock lies within the upper 12 inches
(30 cm) of soil; on well-established plants the rootstock may be up to
1.6 feet (0.5 m) in diameter.  Purple loosestrife is easily identified
in the summer by the showy reddish-purple flowers that occur on terminal
spikelike panicles.  Although the leaves gradually fall after autumn
frosts, the sturdy stems remain standing throughout the winter and into
the next growing season.  After flowering each stem supports a dense
spiralling row of dark-brown seed capsules [8,18,19].


RAUNKIAER LIFE FORM : 
   Cryptophyte


REGENERATION PROCESSES : 
Sexual reproduction:  Purple loosestrife's reproductive capacity is
enormous.  A single flowering stalk can produce 300,000 seeds, and
densities as high as 80,000 stalks per acre (197,600/ha) have been
recorded [7].  The seeds are very small, about 400 x 200 microns, and
weigh 0.5 to 0.6 milligrams [19].  They are primarily dispersed by
water, and become a component of marsh seed banks.  Seeds are also
transported on the fur of aquatic mammals and in the plummage of water
birds.  In a seed bank study in a Minnesota wetland infested with purple
loosestrife, 38,090 purple loosestrife seeds were found per square foot
(410,000/sq m) in the top 2 inches (5 cm) of soil [21].  Many of these
soil-stored seeds germinate on mud flats exposed during marsh drawdown
[14].  The seeds require relatively warm temperatures for germination.
Greater than 80 percent of the seeds germinate at temperatures between
68 and 86 degrees Fahrenheit (20-30 C) [16].  Autumn seed germination is
rare.  Most seedling establishment is from seed germinating in late
spring or early summer.  Spring-established seedlings grow rapidly and
produce flowers 8 to 10 weeks after germination [16].

Vegetative reproduction:  The rootstock is the main organ of
perennation; therefore, wide vegetative spread is unlikely.  However,
detached root or stem fragments can take root and develop into flowering
stems.  Fragments produced by foraging wild animals or mechanical
clipping can contribute to rapid spread by floating to uninfested areas
[7].  Plants also send up new shoots from adventitious buds on the stem
or caudex when aboveground plant portions are injured or destroyed
such as by clipping, crushing, or fire [18].


SITE CHARACTERISTICS : 
Purple loosestrife inhabits open wetland habitats such as marshes, bogs,
fens, sedge meadows, wet prairies, roadside ditches, river and canal
banks, and reservoir edges.  It is shade intolerant and is infrequent
along well-shaded, tree-bordered riverbanks.  It tolerates a wide range
of soil textures, from gravel to clay, and also grows on organic soils.
Purple loosestrife's most common associates, listed in order of
decreasing importance, include:  cattail, reed canarygrass (Phalaris
arundinacea), sedge (Carex spp.), bulrush (Scirpus spp.), rush, willow
(Salix spp.), horsetail (Equisetum fluviatile), common reed (Phragmites
australis), flat sedge (Cyperus spp.), water-plantain (Alisma
plantago-aquatica), and stinging nettle (Urtica dioica) [19].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Purple loosestrife is an aggressive invader of wetlands.  Once
established, it often displaces native wetland species such as cattails,
rushes, and sedges to form self-replacing monotypic stands.  Where
purple loosestrife is competing with cattails, it is favored by
fluctuating water levels because marsh drawdown aids in seedling
establishment.  However, where water levels remain constant and
relatively deep (16 inches [40 cm]) cattails may be able to outcompete
purple loosestrife [14].

Many purple loosestrife stands in the Northeast have maintained
themselves for more than 20 years [18].


SEASONAL DEVELOPMENT : 
Purple loosestrife begins spring growth about a week to 10 days after
cattail and reed canarygrass, its most common associates.  Throughout
the United States, flowering occurs from late June to early September.
The leaves are gradually shed after fall frosts; stems remain standing
throughout the winter [19].

Related categories for Species: Lythrum salicaria | Purple Loosestrife