Seed Production and Viability of Eight Porterweed Selections Grown In
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HORTSCIENCE 44(7):1842–1849. 2009. detrimental generations later if invasion oc- curs (Caley et al., 2008). Desirable attributes of nettleleaf porterweed (Stachytarpheta Seed Production and Viability of cayennensis) are its long period of profuse and vibrantly colored flowers that attract Eight Porterweed Selections Grown butterflies and adaptability to a range of landscape conditions; yet a consequence of in Northern and Southern Florida this is its ability to self-seed and readily naturalize in areas far beyond its planting. Sandra B. Wilson1 Introduced to the United States from Central Indian River Research and Education Center, Fort Pierce, FL 34945 and South America, nettleleaf porterweed has since escaped cultivation in Florida, Gary W. Knox Hawaii, and Puerto Rico (U.S. Department North Florida Research and Education Center, 155 Research Road, Quincy, of Agriculture, 2008). In Florida, herbarium FL 32351 vouchers document its escape in two of the southern-most counties (Wunderlin and Han- Keona L. Muller sen, 2009a). It has been found in 18 conser- Indian River Research and Education Center, Fort Pierce, FL 34945 vation areas in Florida (Gann et al., 2008) and is problematic in other parts of the world, Rosanna Freyre including the Pacific Islands (Pacific Island P.O. Box 110670, Gainesville, FL 32611 Ecosystems at Risk, 2007) and Australia (World Wildlife Fund Australia, 2006). In Zhanao Deng Australia, it was ranked as an environmental Gulf Coast Research and Education Center, 14625 CR 672, Wimauma, FL weed with a score of 4, meaning it has natu- ralized and is known to be a major problem 33598 at three or fewer locations within a state Additional index words. invasive, native, cultivar trialing, flow cytometry, seed germination, or territory (Groves et al., 2005). Florida’s Stachytarpheta jamaicensis, Stachytarpheta mutabilis, Stachytarpheta speciosa, Stachytar- Exotic Pest Plant Council (FLEPPC) desig- pheta cayennensis nates porterweed as a Category II invasive, indicating that it has increased in abundance Abstract. Nettleleaf porterweed (Stachytarpheta cayennensis) is a potentially invasive or frequency but has not yet altered Florida ornamental plant in Florida. Plant growth, visual quality, flowering, and seed viability plant communities to the extent shown by were assessed for nettleleaf porterweed and eight closely related alternatives planted Category I species (FLEPPC, 2007). In 2006, in northern and southern Florida. In northern Florida, ‘Mario Pollsa’ porterweed The University of Florida Institute of Food (Stachytarpheta spp.), ‘Violacea’ porterweed (Stachytarpheta mutabilis), ‘Naples Lilac’ and Agricultural Sciences Status Assessment porterweed (Stachytarpheta spp.), ‘Red Compact’ porterweed (Stachytarpheta speciosa), of Non-native Plants (Fox et al., 2008) rec- and nettleleaf porterweed (Stachytarpheta cayennensis) achieved high flower ratings ommended that porterweed be used with between 4 (average to good flowering) and 5 (abundant flowering, peak bloom) during caution and managed to prevent its escape. 4 or more months. Also, jamaican porterweed (Stachytarpheta jamaicensis), ‘Violacea’ These conclusions were footnoted to empha- porterweed, ‘Red Compact’ porterweed, and nettleleaf porterweed achieved visual size that there was insufficient evidence to quality ratings between 4 and 5 (good to excellent quality) throughout most of the study. fully validate the statement and that the status In southern Florida, the same cultivars received high flower ratings but generally for should be reassessed every 2 years (Fox et al., shorter periods of time. Also, ‘Violacea’ porterweed and ‘Red Compact’ porterweed 2008). consistently received visual quality ratings that were above 4 (good quality, very As alternatives to the resident species desirable). During the course of the 28-week study, nettleleaf porterweed produced the (wild-type form) of nettleleaf porterweed, greatest number of spiked inflorescences with 39% to 80% seed viability. At both there are several other closely related species locations, ‘Violacea’ porterweed did not produce any viable seed and seed viability that have ornamental value such as coral was less than 10% for ‘Mario Pollsa’ porterweed, coral porterweed (Stachytarpheta porterweed (Stachytarpheta mutabilis), ‘Vio- mutabilis), and ‘Naples Lilac’ porterweed. lacea’ porterweed (Stachytarpheta mutabilis), and several dwarf porterweed selections (Sta- chytarpheta speciosa) (Caldwell, 2005). In The invasive plant management program total industry sales in 2005 estimated at $15.2 addition, there is a Florida native jamaican in Florida has contracted over 190 research billion (Hodges and Haydu, 2006). Although porterweed (Stachytarpheta jamaicensis) that projects at a cost of $19.8 million over the the majority of introduced plants do not is distinctively lower-growing with a more last 39 years (Schmitz, 2009). Despite these escape cultivation, some plants become ex- horizontal spread (Gilman, 2007; Hammer, efforts, plant invasions continue to rise. The ceptionally adaptable, regenerate prolifically, 1994). The genus Stachytarpheta has under- State of Florida is the second largest producer and eventually invade natural areas (Parker gone a series of taxonomic revisions that of ornamental plants in the United States with et al., 2007; Reichard and Hamilton, 1997; are further complicated by putative hybrids Williamson and Fitter, 1996). Consequently, (Munir, 1992). In Florida, the Category II the nursery and landscape industry has been invasive nettleleaf porterweed reportedly hy- an unintentional but significant contributor bridizes with the native jamaican porterweed Received for publication 16 July 2009. Accepted to the spread of invasive plants (Burt et al., and is documented as Stachytarpheta ·inter- for publication 22 Sept. 2009. 2007; Culley and Hardiman, 2009; Dehnen- cedens (Wunderlin and Hansen, 2009b). In Indian River Research and Education Center Jour- Schmutz et al., 2007; Fox et al., 2003; Hawaii, Wagner et al. (1999) report that the nal Series No. R-070901. Harrington et al., 2003; Li et al., 2004; Mack hybrid resembles jamaican porterweed more We gratefully acknowledge financial support from and Erneberg, 2002; Niemiera and Von closely than nettleleaf porterweed, but the the Florida Department of Environmental Protec- tion. We extend gratitude to Patricia Frey and Holle, 2009; Pemberton and Liu, 2009; corollas are darker in color than jamaican James Aldrich for providing field and technical Reichard and White, 2001). The same qual- porterweed with a more erect habit and more assistance throughout the study. ities that often prompt exotic ornamental ovate and darker green leaves. Wagner et al. 1To whom reprint requests should be addressed; introductions (short juvenility, long flower- (1999) also report that nettleleaf porterweed e-mail sbwilson@ufl.edu. ing, fast growth, ease of propagation) can be hybridizes with coral porterweed. Munir 1842 HORTSCIENCE VOL. 44(7) DECEMBER 2009 (1992) report that S. ·intercedens actually of the FLEPPC Category II invasive nettleleaf and one time per week in summer). Plants evolved by the hybridization of indian snake- porterweed and seven closely related potential were fertilized 6 weeks after planting with weed (Stachytarpheta indica) and jamaican alternatives planted in northern Florida 57 g of 12-month 15N–3.9P–10K Osmocote porterweed. Hybridization potential between (Quincy, USDA Plant Hardiness Zone 8b) Plus (Scotts Co., Marysville, OH) in the area native and invasive species of the same genus and southern Florida (Fort Pierce, USDA Plant 15 to 30 cm from the crown. Daily rainfall, is of particular concern. For example, the Hardiness Zone 9b). Specific objectives in- temperature, and solar radiation were re- FLEPPC Category I invasive lantana (Lantana clude: 1) assessment of plant performance, corded by Florida Automated Weather Net- camara) has extensively hybridized with all growth, and flowering among cultivars; 2) work monitoring stations located at each site. three distinct varieties of the Florida native determination of seed production, viability, Field conditions for southern Florida were as pineland lantana (Lantana depressa), contam- and germination among cultivars; and 3) follows: Ankona sand with 0.8% organic inating the endemic gene pool (Langeland and confirmation of ploidy number and potential matter, pH 6.8, average monthly rainfall Craddock Burks, 1998). Schierenbeck and for hybridization between the native and in- 18.8 cm, mean minimum and maximum Ellstrand (2009) have reviewed numerous vasive species. temperatures 14.2 and 33.4 °C, respectively, examples in which hybridization preceded and 80.9% relative humidity. Field condi- the emergence of successful invasive popula- Materials and Methods tions for northern Florida were as follows: tions. Controlled plant breeding has been used Carnegie loamy fine sand with 2.6% organic to develop numerous new noninvasive plants Plant material and field conditions. Eight matter, pH 4.7, average monthly rainfall 14.6 (with improved commercial traits) in several porterweed species or cultivars were selected cm, mean minimum and maximum tempera- states, including North Carolina (Ranney, for this study based on local availability tures 9.3 and 33.7 °C, respectively, and 2004), Connecticut (Li et al., 2004), and (Table 1). Seed- propagated jamaican porter- 77.0% relative humidity. Florida (Czarnecki et al., 2008). Stachytar- weed and clonally propagated coral porter- Visual quality, flowering, and plant pheta