










Invasive 
plant 
profile 
Noel Pavolvic 
The lovely fruits of 
American bittersweet, a 
plant we called ‘Fertile 
Myrtle’ at the Indiana 
Dunes. 
Volume 28, Number 2 
inps journal 
Indiana Native Plant Society 
Summer 2021 

A Bittersweet Tale of Two Lianas 
By Noel B. Pavlovic 
Oh, the lovely American bittersweet (Ce/astrus 
scandens, Celastraceae) — a woody vine (liana) 
that produces bright clusters of orange fruits at its 
branch tips. The fruits are stunning and capture 
the attention of anyone that sees them in the fall. 
American bittersweet is confined to the eastern 
half of the United States and has been declining 
in the Northeast and Atlantic seaboard. Formerly it 
was found along fencerows, forested pond edges, 
and disturbed forest areas as well as in open 
habitats. Around 2000, | realized that the open 
sand dunes of the Great Lakes were a refuge 
for American bittersweet, and this observation 
opened opportunities for new research. 
The major woe for American bittersweet is its 
cousin, Asiatic bittersweet (Celastrus 
| orbiculatus). After its introduction 
to New York City in 1874, Asiatic 
| bittersweet expanded in gardens and 
| later was picked up by the floral trade 
k " 4 m . oe 
oe = | for fall floral decorations (Del Tredici 
r | 2014). This invasive species strangles 
se) and kills trees and alters vegetation 
succession. Unlike the native species, 
am which only produces fruit at branch 
tips, Asiatic bittersweet produces 
clusters of flowers and fruits in almost every 
leaf axil. The characteristics that allow American 
bittersweet to survive in coastal dune habitats, 
namely stress tolerance and slow growth, are 
inimical to the floral trade that desires the ramped 
growth of the Asiatic species. When Wrigley Field 
in Chicago was constructed it was realized that 
the Boston ivy would not be able to cover the 
outfield brick wall in time for opening day, so fast 
growing Asiatic bittersweet was planted while the 
Boston ivy could mature in size (Will 2014). 
Asiatic bittersweet was introduced into the 
Indiana Dunes between the town of Dune Acres 
and the Indiana Dunes State Park in the 1950- 
60’s where it was confined when | arrived in 1983. 
By 2000, it occupied 2.4% of the dunes landscape 
and by 2012 had increased to 26.9% of the 

landscape. Although Asiatic bittersweet prefers 
shaded habitats, our research showed it could 
invade prairies and savannas (Leicht-Young et al. 
2013). Once humans brought Asiatic bittersweet 
to the dunes, native birds began to disperse the 
seeds in the fall after the bittersweet arrangements 
were discarded onto brush piles. 
In 2005, I, and fellow research colleagues, 
started to answer fundamental questions 
regarding the relationships between the two 
bittersweets, including how to confidently tell them 
apart throughout the year. In our first study we 
Pekytels 
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Book Reviews 
Ot iy4=)pmelel(-1ale= 
Invasive Plant Profile 1 
INPS at Work ) 
Native Plant Profiles 12, 16 
Natural Area (Artist's Reflection) 
Naturalist Profile 
mate lalan | Bam keye) ts 
10-11 
14-15 
3,7 
found that we could only distinguish the plants 
by mature leaves 90% of the time (Leicht-Young 
et al. 2007). Strikingly, though, the first leaves 
of the year emerge differently between the two: 
American bittersweet leaves unroll as two sides 
of a scroll (involute or in-rolled) while Asiatic 
bittersweet leaves emerge as pages of a book 
(conduplicate, two folded against each other). 
Later leaves of both species emerge in the same 
fashion (conduplicate; see USGS 2021). The 
confusion of species identification has in part led 
to the selling of Asiatic bittersweet as American 
bittersweet; 53% of 18 plants were misidentified 
and 7 of 11 nurseries sold misidentified plants 
(Zaya et al. 2017). 
Our second research question was whether 
hybridization between the two species might be 
compromising our native bittersweet. We found, 
genetically, that the two species hybridized but 
Lianas - continued on page 2 
