Biology Reference
In-Depth Information
Lumer and Yost (1995) often found adjoining plants that were connected by “hori-
zontal underground stems” growing at a depth of nearly 50 cm.
Both swallow-wort species, and PSW in particular, have high seed output poten-
tials. At a heavily infested site in northern New York State, Smith (2006) reported a
potential seedling output of 63,439 seedlings/m
2
when polyembryonic offsprings
were taken into account. However, it is not clear whether newly emerged or older
seedlings contribute more relatively to the expansion of swallow-wort patches. Ladd
and Cappuccino (2005) found that when they planted (buried 1 cm) overwintered
PSW seeds in an experimental old field, 71% of the seeds germinated in the first year.
Swallow-wort seeds generally mature dormant, and while experimentally germina-
tion can be doubled in seeds provided with a cold treatment, the nature and extent of
this dormancy is unknown (DiTommaso et al. 2005a, b; Lumer and Yost 1995).
13.4
Introduction and Current Distributions
The earliest North American collection of PSWs was made in 1885 from Victoria,
British Columbia (DiTommaso et al. 2005b; Sheeley and Raynal 1996). The earli-
est collection in the USA was 6 years later (1891), when it was simultaneously
recorded in both Monroe and Nassau Counties in New York state. The first speci-
men of BSW in North America was collected in Ipswich, Massachusetts (MA) in
1854. In Gray's 1867
Manual of Botany
, BSW was cited as a garden escape in
Cambridge, MA. By 1871 there was a report of the plant “running wild” along a
road in what is now likely Flatlands, in modern day Brooklyn, New York
(Anonymous 1871). Eleven years later, it was described as naturalized in West
Point and New Rochelle, NY (Bailey 1882; Day 1881).
The most likely source of introduction of both species was importation as speci-
mens for botanical or estate gardens, though this remains uncertain (DiTommaso
et al. 2005b; Sheeley 1992). For many years the two swallow-wort species were
cultivated and sold as ornamental plants, though this is no longer common
(DiTommaso et al. 2005b; Monachino 1957).
PSW invasion in North America is centralized in upstate New York, specifically
Central New York, the Finger Lakes Region, and the region surrounding Lake Ontario
in both the USA and southern Canada. There are additional extensive populations
throughout Long Island, NY and other states in the Northeast, and there have been
isolated reports of plant sightings in Indiana, Michigan, Missouri, and Wisconsin
(DiTommaso et al. 2005b; Weston et al. 2005). BSW has a wider distribution longi-
tudinally, with populations reported as far west as Kansas, Nebraska, Minnesota, and
even California. However, its invasion is also centered in New York, with the heaviest
infestations found in the Hudson River Valley, but also in Massachusetts and
Connecticut (DiTommaso et al. 2005b). The wider distribution of BSW has been
attributed to its apparent ability to adapt to more severe climatic conditions than
encountered in its native Mediterranean range, unlike PSW that has largely remained
within its predicted climatic boundaries (DiTommaso et al. 2005b).
