Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

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THE ECOLOGY AND SPREAD OF INVASIVE SWALLOW-WORT SPECIES ACROSS
NY STATE: DO ALLELOPATHY AND GENOTYPE PLAY A ROLE? C.H. Douglass and
L.A. Weston, Cornell Univ., Ithaca, NY.
ABSTRACT
Pale swallow-wort (Vincetoxicum rossicum (Kleopow) Barbar.) and black
swallow-wort (V. nigrum (L.) Moench) are herbaceous perennial vines introduced to the
Northeastern U.S. from their native ranges in Eastern Europe and the Iberian Peninsula,
respectively. While black swallow-wort can be found throughout the Northeast, from
Long Island to Maine and west to St. Lawrence County in New York State, pale
swallow-wort is most common in southern Ontario, Canada and Central N.Y. State,
especially in the Finger Lakes region. Both species invade forest understories in
unmanaged natural areas, but are becoming increasingly problematic in tree nurseries,
fallow fields, and no-till cropping systems. Published reports have identified the potential
allelopathic ability of these two swallow-wort species as possibly playing a significant
role in their invasibility and increased competitiveness. Furthermore, numerous
secondary metabolites (primarily alkaloids) with potent fungicidal or cytotoxic effects in
mammalian systems have been extracted from swallow-wort foliar tissues. In order to
test whether the two swallow-worts are indeed allelopathic, we designed a number of
laboratory bioassays to examine the source and activity of bioactive secondary products
in each species. Preliminary findings indicate up to a thirty percent decrease in root
elongation of large crabgrass (Digitaria sanguinalis) seedlings when grown in the
presence of seedlings of both swallow-wort species.
Both swallow-wort species display a high degree of phenotypic plasticity in
natural settings, particularly with respect to leaf size, shape and surface characteristics,
which may be related to their ability to adapt to diverse settings. Given that the
swallow-worts are prolific cross pollinators and seed producers, it is likely that
introduced populations exhibit some degree of genetic diversity. We are currently
examining inter- and intra-population phenotypic plasticity as well as genetic diversity in
populations collected across NY, in an attempt to examine factors likely associated with
invasibility.
By comparing standard measures of phenotype (leaf shape index, flowering time,
flower color, node number) and genetic distance between and within swallow-wort
populations, we can further characterize the NY populations of both species of swallowwort.
Characterization will allow us to examine the recent spread of both species and
their potential species similarities and differences, including reproductive success,
which may involve successful hybridization of the two species in increasingly
overlapping ranges.
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