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Praxelis clematidea (Asteraceae): A New Plant Invader of Florida
Amber G. Gardner and Kent A. Williges

Southeastern Naturalist, Volume 14, Issue 1 (2015): N21–N27

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N21 2015 Southeastern Naturalist Notes Vol. 14, No. 1 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 2015 Southeastern Naturalist Notes Vol. 14, No. 1 N22 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 N23 2015 Southeastern Naturalist Notes Vol. 14, No. 1 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. 2015 Southeastern Naturalist Notes Vol. 14, No. 1 N24 A.G. Gardner and K.A.Williges 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. N25 2015 Southeastern Naturalist Notes Vol. 14, No. 1 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. Literature Cited Abbott, J.R., C.L. White, and S.B. Davis. 2008. Praxelis clematidea (Asteraceae), a genus and species new for the flora of North America. Journal of the Botanical Research Institute of Texas 2(1):621–626. 2015 Southeastern Naturalist Notes Vol. 14, No. 1 N26 A.G. Gardner and K.A.Williges Animal and Plant Health Inspection Service (APHIS). 2012. Plants for planting quarantine pest evaluation data sheets. Technical report. US Department of Agriculture, APHIS Plant Protection and Quarantine, Riverdale, MD. 64 pp. Available online at http://www.regulations.gov/#!documentD etail;D=APHIS-2011-0072-0045. Accessed 18 December 2013. Bissett, N.J. 2004. Upland habitat restoration plan for the Moody Branch Mitigation Park Wildlife and Environmental Area. Special technical report. The Natives Inc., Davenport, FL. 19 pp. Center for Invasive Species and Ecosystem Health (CISEH). 2011. Early detection and distribution mapping system (EDDMapS). University of Georgia. Available online at http://www.eddmaps. org/. Accessed 24 February 2014. Corlett, R.T., and J.C. Shaw. 1995. Praxelis clematidea: Yesterday South America, today Hong Kong, tomorrow the world? Memoirs of the Hong Kong Natural History So ciety 20:235–236. Department of Agriculture, Fisheries, and Forestry (DAFF). 2014. Praxelis Praxelis clematidea fact sheet PP113 January 2014. The State of Queensland, Australia. 2 pp. Available online at http:// www.daff.qld.gov.au/__data/assets/pdf_file/0019/63172/IPA-Praxelis-PP113.pdf. Accessed 24 February 2014. Department of Environment and Heritage Protection (DEHP). 2014. Zieria obovata. WetlandInfo. The State of Queensland, Australia. Available online at http://wetlandinfo.ehp.qld.gov.au/wetlands/ ecology/components/species/?zieria-obovata. Accessed 14 February 2014. Dwyer, N., S. Glass, J. McCollom, and K. Marois. 2010. Groundcover restoration implementation guidebook. Special technical report. Florida Fish and Wildlife Conservation Commission, Tallahassee, FL. 64 pp. Florida Exotic Pest Plant Council (FLEPPC). 2013. List of invasive plant species. Available online at http://www.fleppc.org/list/11list.html. Accessed 11 March 2014. Gates, C.A. 2006. Hilochee Wildlife Management Area groundcover restoration plan, Ray Ranch Parcel. Special technical report. Florida Fish and Wildlife Conservation Commission, Clermont, FL. 14 pp. Hutchinson, J.T. 2003. Invasive plants of Archbold Biological Station and Highlands County, Florida. Available online at http://www.archbold-station.org/station/html/linkpgs/invasiveplants.html. Accessed 18 March 2014. Lohrer, F.E., and H.M. Swain. 2000. Endangered, threatened, or rare species of the Lake Wales Ridge, central Florida. Available online at http://www.archbold-station.org/fai/species4.html. Accessed 12 March 2014. Space, J.C., D.H. Lorance, and A.M. LaRosa. 2009. Report to the Republic of Palau: 2008 update on invasive plant species. Report. US Department of Agriculture Forest Service, Pacific Southwest Research Station Institute of Pacific Islands Forestry, Hilo, HI. 227 pp. Available online at http:// hear.its.hawaii.edu/pier/pdf/Palau_report_2008.pdf. Accessed 28 March 2014. Tasker, A. 2010. 2009–2010 update on the federal noxious weed regulatory program. Weeds Across Borders conference. US Department of Agriculture Animal and Plant Health Inspection Service, Plant Protection and Quarantine, Riverdale, MD. 38 pp. US Fish and Wildlife Service (USFWS). 2011. Lake Wales Ridge NWR. Available online at http:// www.fws.gov/lakewalesridge/. Accessed 12 March 2014. Veldkamp, J.F. 1999. Eupatorium catarium, a new name for Eupatorium clematideum Griseb., non Sch.Bip (Compositae), a South American species naturalized and spreading in SE Asia and Queensland, Australia. Gardens’ Bulletin Singapore 51:119–124. Wang, Z.H., Q.B. Chen, A.Q. Ye, and H. Zhang. 2008. First report of a phytoplasma associated with Praxelis witches’ broom in China. Plant Pathology 57(2):364. Waterhouse, B.M. 2003. Know your enemy: Recent records of potentially serious weeds in northern Australia, Papua New Guinea, and Papua (Indonesia). Telopea 10(1):477–485. Waterhouse, B., R. McFadyen, A. Holland, and J. Thorp. 2003. Weed management guide: Praxelis- Praxelis clematidea. CRC Weed Management. 4 pp. Available online at http://www.environment. gov.au/biodiversity/invasive/weeds/publications/guidelines/alert/p-clematidea.html. Accessed 14 February 2014 Weekley, C.W., E.S. Menges, and R.L. Pickert. 2008. An ecological map of Florida’s Lake Wales Ridge: A new boundary delineation and an assessment of post-Columbian habitat loss. Florida Scientist 71(1):45–64. N27 2015 Southeastern Naturalist Notes Vol. 14, No. 1 A.G. Gardner and K.A.Williges Williges, K., J. Freeman, A. Gardner, and M. Stevens. 2011. Vegetation monitoring at FFWCC native ground cover restoration sites July 2010–December 2010 (2010 NGCR monitoring report). Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, Gainesville, FL 122 pp. Wunderlin, R.P., and B.F. Hansen. 2011. Guide to the Vascular Plants of Florida, Third Edition. University Press of Florida, Gainesville, FL. 784 pp.