Biology Reference
In-Depth Information
13.1 Introduction
Black swallow-worts (BSW) and pale swallow-worts (PSW) are invasive, herbaceous
perennial vines that were introduced over a century ago into North America. Currently
both species are on banned or prohibited plant species lists in Connecticut,
Massachusetts, and New Hampshire, and BSW is classified as a “noxious” weed in
Vermont (USDA Plants Database 2008). Like many invasive species, the two swal-
low-worts exhibit numerous attributes of ideal weeds (Baker 1974). That is, they are
strong competitors for available and sometimes scarce resources, are prolific repro-
ducers, and can significantly alter invaded habitats (Ernst and Cappuccino 2005;
Greipsson and DiTommaso 2006; Smith 2006). The focus of our research on the
swallow-wort species has been to better understand the specific similarities and dif-
ferences among these two congeneric species and evaluate if there is a physiological
or genetic basis for their rapid invasion in regions of North America. This chapter is
a summary of the literature that has been presented with respect to both species, and
in addition, an overview of our recent work related to their spread, allelopathic poten-
tial, and genetic diversity among populations in New York. By developing a broader
understanding of a plant species' biology and ecology in particular locations, we can
try to develop more effective strategies for the management of these species and other
problematic nonnative invaders, which have thus far evaded effective control.
Unlike some more infamous plant invaders, swallow-worts produce small flow-
ers and their often prostrate growth habit allows them to easily blend in with resi-
dent vegetation. Swallow-worts often persist largely unnoticed by landowners or
managers until they are well established and have displaced prior vegetation
(Lawlor 2003; West and Fowler 2008). Mature vines can grow to several meters in
length, and infestations can often become dense impenetrable thickets of inter-
twined vines (hence the common name synonym dog-strangling vine) (DiTommaso
et al. 2005b; Sheeley and Raynal 1996). Most significantly, cultural control meth-
ods that effectively reduce mature infestations are not available at present. Current
recommendations for control are limited to the use of broad-spectrum herbicides
and mechanical controls that must be repeated both during the growing season and
annually for several years. Unfortunately, even these laborious and expensive strat-
egies only provide reliable and sometimes temporary control of smaller satellite
populations (Averill et al. 2008; Lawlor and Raynal 2002; Weston et al. 2005).
13.2 Taxonomy
PSW [
Vincetoxicum rossicum
(Kleopow) Babar. =
Cynanchum rossicum
(Kleopow)
Borhidi] and BSW [
Vincetoxicum nigrum
(L.) Moench =
Cynanchum nigrum
(L.)
Pers. =
Cynanchum louiseae
(L.) Kartesz & Gandhi] are generally placed in the
Asclepiadaceae (Gleason and Cronquist 1991; USDA Plants Database 2008). Recent
work, however, suggests that the species should more accurately be placed in the
