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A.G. Gardner and K.A. Williges
Praxelis clematidea (Asteraceae): A New Plant Invader of Florida
Amber G. Gardner1,* and Kent A.Williges1
Abstract - Praxelis clematidea (Praxelis; Asteraceae), a native of South America, was first discovered
in Florida in Orange County in 2006; it has now been confirmed in 6 other counties: Hardee, Hillsborough,
Lake, Manatee, Osceola, and Polk counties. These populations are concentrated around the
Lake Wales Ridge (LWR) region and may pose a threat to the already imperiled flora and fauna of the
LWR. An assessment of the threat to the LWR and other Florida ecosystems is essential, and control
methods must be evaluated for Florida before the species becomes an insurmountable problem. Our
goal is to inform the people of Florida of the threat of Praxelis and to urge them to report any populations
so they can be controlled or eradicated.
Voucher specimen data: United States. Florida. Lake County: Found growing
in a weedy fencerow along the southern border of a wildlife food plot at Hilochee Wildlife
Management Area (WMA), 12932 CR 474, in Clermont, ~350 m WSW of the field office
on Yancey Road. Was surrounded by Vitis rotundifolia Michx. (Muscadine Grape), Rubus
spp., and Smilax spp. Suffrutescent herb 0.5–1 m tall; flowers pale bluish-purple; forming
dense patches. Exudes strong odor of cat urine when stem or leaves are crushed. Frequency:
occasional. Growing in fairly isolated but dense patches throughout the property and along
the roadside on a Native Ground Cover Restoration (NGCR) site. Lat. 28°21′36.55″N,
Long. 81°44′9.55″W. Datum: WGS84. Collected by Amber G. Gardner and Sarah J. Smith,
6 December 2012. [FLAS 236906, FLAS 236907]. Manatee County: Found growing in the
southwest corner of an NGCR site, adjacent to a citrus grove at Moody Branch Mitigation
Park Wildlife and Environmental Area (10146 303rd Avenue, Parrish, FL 34219). Was in an
area surrounded by hog damage and Eupatorium capillifolium (Lam.) Small (Dogfennel).
Suffrutescent herb about 0.5 m tall; flowers pale bluish-purple. Exudes strong odor of cat
urine when stem or leaves are crushed. Frequency: rare. This was the only individual encountered
at the NGCR site, but it is possible that the adjacent orange grove may have been
the source. Approximate Coordinates: Lat. 27°38′19.92″N, Long. 82°15′2.34″W. Datum:
WGS84. Collected by Amber G. Gardner, 14 October 2013. [FLAS 241537] (Table 1).
Praxelis clematidea (Kuntze) R.M. King and H. Rob. (Praxelis), a native of South America,
was first discovered in Florida in 2006. Until recently, the only record of this plant in
North America was from Orange County, FL, where University of Florida researchers found
it growing in several disturbed localities (Abbott et al. 2008). Florida Fish and Wildlife’s Fish
and Wildlife Research Institute (FWRI) staff have been unknowingly encountering Praxelis
in a Native Ground Cover Restoration (NGCR) site on Hilochee WMA since June 2007. This
site is located in Lake County about 9 miles south of Clermont. For several years, FWRI
staff had confused this plant with the morphologically similar Conoclinium coelestinum (L.)
DC. (Blue Mistflower) and Ageratum houstonianum Mill. (Bluemink) (Abbott et al. 2008).
With the release of the Guide to the Vascular Plants of Florida Third Edition (Wunderlin and
Hansen 2011), and after finding Abbott et al.’s (2008) publication of their Praxelis discovery,
we soon realized that we had misidentified a species new to Florida, and that it was more
1Florida Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission,
1105 Southwest Williston Road, Gainesville, FL 32601. *Corresponding author - amber.gardner@
myfwc.com.
Manuscript Editor: Brett Serviss
Notes of the Southeastern Naturalist, Issue 14/1, 2015
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A.G. Gardner and K.A.Williges
widespread than originally thought. Several voucher specimens were collected in December
2012 and submitted to the University of Florida herbarium for identification.
At 9369 acres, Hilochee WMA encompasses many different plant communities. The approximately
87-acre NGCR site was historically mesic flatwoods but had been converted to
semi-improved pasture long before restoration efforts began in 2005 (Gates 2006). The soils
are primarily Myakka and Pomello sand (Gates 2006). Based on our vegetation-monitoring
data from the restoration area over the past 6 years, we feel that the main area of infestation
of Praxelis is the northern ~30 acres in areas where Aristida stricta Michx. (Pineland Threeawn)
and other native groundcover species are not as well established as in the southern
portion. The northern portion harbors several ruderal and exotic species including Melinis
repens (Willd.) Zizka (Rose Natal Grass), listed as a category I exotic by the Florida Exotic
Pest Plant Council (FLEPPC 2013), and several other less-noxious exotics including Paspalum
notatum Alain ex Flüggé (Bahiagrass), Sporobolus indicus (L.) R. Br. (Smutgrass),
and Richardia brasiliensis Gomes (Tropical Mexican Clover) (Williges et al. 2011).
In addition to the plants at the Hilochee site, FWRI biologists discovered a new incidence
of Praxelis during an assessment of another restoration site at Moody Branch Wildlife
and Environmental Area in Manatee County in October 2013. This site was a former agricultural
field that is being restored to mesic flatwoods (Dwyer et al. 2010). A variety of soil
types can be found near the restoration site: Tavares Fine Sand, Duette Fine Sand, Pomello
Fine Sand, Waveland Fine Sand, and Delray-Pomona Complex (Bissett 2004). This field
shares its western border with a Citrus grove that harbors invasive exotics including Rose
Natal Grass. Only a single Praxelis individual was encountered in the field’s southwest corner.
The plant was collected, pressed, and submitted to the University of Florida herbarium
Table 1. Praxelis clematidea herbarium voucher data from University of Florida and University of
South Florida.
Accession # Collectors County Date
FLAS 220203 LeAnn White 1 Orange 26 July 2006
USF 258417 J. Richard Abbott 22888 with Melissa Clark Orange 17 July 2007
FLAS 222413 J. Richard Abbott 22887 [coll. with] Tim Orange 17 July 2007
Burns and Melissa Clark
FLAS 222414 J. Richard Abbott 22887 [coll. with] Tim Orange 17 July 2007
Burns and Melissa Clark
FLAS 222415 J. Richard Abbott 22888 [coll. with] Melissa Orange 17 July 2007
Clark
FLAS 222416 J. Richard Abbott 22888 [coll. with] Melissa Orange 17 July 2007
Clark
FLAS 222417 J. Richard Abbott 22888 [coll. with] Melissa Orange 17 July 2007
Clark
FLAS 227195 J. Richard Abbott 24194 [coll. with] Kurt and Orange 8 March 2008
Julie Neubig
FLAS 233219 J. Richard Abbott 24952 Orange 10 September 2008
FLAS 236906 Amber G. Gardner and Sarah J. Smith Lake 6 December 2012
FLAS 236907 Amber G. Gardner and Sarah J. Smith Lake 6 December 2012
FLAS 238125 Lavonda Rogers Hardee 17 April 2013
USF 272732 S. Dickman s.n. Hillsborough 25 Jun 2013
FLAS 241537 Amber G. Gardner Manatee 14 October 2013
USF 270974 C. Cook s.n. Polk 18 November 2013
USF 273922 D. Stone s.n. Osceola 13 May 2014
USF 273635 S. Dickman s.n. Hillsborough 19 May 2014
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A.G. Gardner and K.A.Williges
for confirmation and as a new county record voucher for Florida. Furthermore, a review of
specimens at the University of Florida and University of South Florida herbaria indicated
that Praxelis had been recently confirmed in Hardee, Hillsborough, Osceola, and Polk counties
as well (Table 1, Fig. 1).
In Florida, Praxelis is morphologically similar to the native species Chromolaena odorata
(L.) R.M. King and H. Rob. (Siamweed), Fleischmannia incarnata (Walter) King and
H. Rob. (Pink Thoroughwort), and Blue Mistflower, as well as the exotic species Ageratum
conyzoides L. (Tropical Whiteweed) and Bluemink (Abbott et al. 2008). The likelihood of
misidentification is probably the reason Praxelis has remained unknown in Florida. Such
confusion with similar species, e.g., Tropical Whiteweed and Bluemink, has occurred in
Queensland, Australia, and in Hong Kong and led to the delayed discovery of Praxelis infestations
in those areas (Corlett and Shaw 1995, Waterhouse 2003). Praxelis has a strongly
conical receptacle, which differentiates it from Pink Thoroughwort and Siamweed. However,
Blue Mistflower and Blue Mink also share this feature. Blue Mink lacks a pappus whereas
Blue Mistflower and Praxelis both have a pappus of capillary bristles. Praxelis differs from
Blue Mistflower in having striated phyllaries that are deciduous and a very strong odor similar
to cat urine when the plants are crushed (Fig. 2). For a more in-depth description and key to
distinguish between the similar Florida species, see Abbott et al. (2008).
The US Department of Agriculture’s Animal and Plant Health Inspection Service
(APHIS) has labeled Praxelis as a pest plant because of its potential for agricultural and
environmental damage in Florida and several other states (APHIS 2012, Tasker 2010).
Praxelis is a prolific seeder, can reproduce by vegetative propagules, and thrives under
Figure 1. Distribution of vouchered Praxelis clematidea populations in Florida based on University
of Florida and University of South Florida herbarium specimens.
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many conditions, including a variety of soil types and ecosystems (disturbed or intact)
and areas denuded by fire (APHIS 2012). Some of these attributes have been observed on
Hilochee WMA, where a flush of Praxelis was documented following a prescribed burn.
So far, it seems to invade only areas with bare ground or disturbance and has yet to spread
into areas with intact native groundcover (Mike Blondin, Hilochee WMA, FL, pers.
comm.). Because it has only been recently discovered in North America, almost nothing is
known about the threat it poses to Florida’s plants and ecosystems. It is of special concern
that it seems to be encroaching on the Lake Wales Ridge (LWR). The LWR spans several
counties including Lake, Polk, Highlands, Orange, Osceola, and Hardee counties (Weekley
et al. 2008), 5 of which have confirmed populations of Praxelis. The LWR is home to
nearly 30 federally listed species, most of which are plants, and more than 40 endemic
invertebrates (USFWS 2011). Much of the LWR has already been lost or fragmented due
to development and agriculture (Lohrer and Swain 2000), and it is under constant threat
from invasive plants. For example, Archbold Biological Station (ABS), located on the
southern part of the LWR, has documented 30 category I and II plants from the FLEPPC
List of Invasive Species on its property, many of which, including Imperata cylindrica
(L.) Raeusch (Cogon Grass) and Abrus precatorius L. (Rosary Pea), are known to invade
xeric habitats (e.g., scrub and sandhill) (Hutchinson 2003). With known Praxelis populations
in relatively close proximity to sensitive scrub areas, several questions need to be
answered: Does this species pose a threat to the endemic and imperiled flora and fauna of
the LWR? Can it invade relatively intact scrub communities, or will it remain in the more
mesic areas? How do we get rid of it?
Figure 2. Photograph of Praxelis clematidea showing leaf shape and arrangement as well as stem
pubescence, with inset showing inflorescence with striated phyllaries. Photo credit: FWRI staff 2014.
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A.G. Gardner and K.A.Williges
Veldkamp (1999) suggests that Praxelis may be somewhat resistant to frost, drought,
and herbicides. The State of Queensland Department of Agriculture, Fisheries, and Forestry
(DAFF) recommends the use of herbicides to control infestations followed by careful
monitoring for regrowth, rather than pulling by hand, which might increase the spread of
seeds and thus the area of infestation. Suggested herbicides include glyphosate, fluroxypyr,
metsulfuron-methyl, and a mixture of 2,4-D and picloram, but the effectiveness of any of
these herbicides has not been reported in the literature (DAFF 2014). Researchers in China
are investigating biological control pathogens that seem to stunt growth and render Praxelis
sterile (Wang et al. 2008). Land managers in Florida are just beginning to evaluate methods
of control. Early reports from Hilochee WMA indicate that Praxelis was easily killed by a
3% glyphosate mixture, but the population seemed to rebound from seeds (Mike Blondin,
pers. comm.). The same treatment was applied at the Nature Conservancy’s Disney Wilderness
Preserve in Kissimmee, FL, but according to Debi Stone (Restoration Steward,
Disney Wilderness Preserve, Kissimmee, FL, pers. comm.) the 3% glyphosate solution only
seemed to top-kill Praxelis plants, which were resprouting from the base within 4 to 6 weeks
after treatment. Multiple treatments will most likely be necessary.
Awareness is key to preventing Praxelis infestations, and, in this respect, Florida and the
United States have an advantage over Australia. Praxelis was first discovered in Queensland
in 1993, but it had likely been there for 20 years or more and spread nearly unchecked before
it was accurately identified. Thus it has become a serious problem there (Waterhouse
et al. 2003), threatening vulnerable native species such as Zieria obovata (C.T. White) J.A.
Armstr. (DEHP 2014). However, in Palau, where Praxelis was unintentionally introduced
during road construction, the infestation was identified early, and eradication efforts using
herbicide seem to have been successful (Space et al. 2009). We are hoping that Early Detection
and Rapid Response (EDRR) efforts can help get Praxelis under control in Florida.
Although it is not known how long Praxelis has been in Florida or how it was introduced,
we know that it has been here for at least 8 years and it may be spreading. It is hard to
say whether new reports of Praxelis are an indication that the species is expanding its range
or whether more positive identifications are being made as a result of new information that
has recently become available. Our goal is to inform scientists and land managers that the
distribution of Praxelis is more extensive than originally thought and that steps must be taken
now to control this species before it encroaches on the LWR. Herbicides must be evaluated
in order to determine optimum control methods, and areas of infestation must be monitored
for further signs of spread. Any Praxelis lookalike, including Blue Mistflower, Siamweed,
Pink Thoroughwort, Tropical Whiteweed, and Bluemink, found in central Florida should be
inspected. New infestations can be reported online at the Early Detection and Distribution
Mapping System (EDDMapS); CISEH 2011).
Acknowledgments. We thank University of Florida herbarium staff for assistance in confirming
the species identification of our specimens and Mike Blondin from Hilochee WMA
for access to the property, his assistance with locating specimens, and sharing his experience
with Praxelis control and behavior. We also thank Debi Stone from The Nature Conservancy’s
Disney Wilderness Preserve in Kissimmee Florida for sharing her experience with Praxelis
and the two anonymous reviewers for their helpful comments and suggestions.
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