Characterizing Potential Invasiveness of Fourteen Buddleja Cultivars in South Florida

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Characterizing Potential Invasiveness of Fourteen Buddleja Cultivars in South Florida
Moller, Dana
Wilson, Sandra ( Mentor )
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Gainesville, Fla.
University of Florida
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Characterizing Potential Invasiveness of Fourteen Buddleja Cultivars in
South Florida

Dana Mollter


Plant growth, visual quality, flowering, and seed production were determined for 14 Buddleja species.

Buddleja davidii x B. lindleyana and B. x weyeriana 'Honeycomb' had the greatest growth index and shoot dry

weight of all cultivars. Each of the 14 cultivars evaluated produced seed. The shape and number of seed pods

per infructescence varied with cultivar. The influence of light and temperature on germination were determined for

6 Buddleja davidii cultivars. Regardless of temperature or cultivar, light was required for germination. With or

without light, less than 2% germination occurred at 33 OC for each cultivar. At 15 or 24 OC in light, germination

was greatest for 'Nanho Purple' followed by 'Dartmoor'. Germination of 'Black Knight' and 'White Profusion'

was consistently lower than that of other cultivars, regardless of temperature.


The State of Florida is the second largest producer of ornamental plants in the U.S. with an estimated 9.908 billion

in total industry sales during 2000 (Hodges and Haydu, 2002). While most intentionally introduced species remain

in their cultivated settings, some escape cultivation and invade natural areas. Many of the plants that are

invasive today were originally introduced as ornamentals and highly prized by both producers and consumers for

their rapid growth, durability, and ease of propagation. Of the 235 woody plant species that have escaped

cultivation and naturalized in North America, 85% were introduced primarily for the landscape trade (Reichard

and Hamilton, 1997). Of the 124 plant species listed as invasive by the Florida Exotic Pest Plant Council

(FLEPPC), 67% were introduced as ornamentals ( Today, approximately 1.9 million acres of

Florida's remaining natural areas have been invaded by exotic plant species and more than 240 million dollars

have been spent in Florida to control invasive, exotic plant species since 1980 (

The Tampa Bay Wholesale Growers, Florida Nurserymen and Growers Association, and the American Nursery

and Landscape Association Board of Directors are among the first in the nation to adopt voluntary codes of

conduct for the nursery industry with regards to invasive plants ( The codes of conduct

involve adoption of risk assessment methods that consider plant characteristics and prior observations or

experience with the plant elsewhere in the world before it is released and distributed. Research on invasive plants

is critical to provide scientific evidence of whether a plant is currently invasive or has great potential to

become invasive. This information can then be relayed to the growers, who in turn can make an informed decision

as to whether or not a particular plant should be produced commercially.

It has been shown that seed production and viability vary significantly across cultivars of wildtype plants

(Krumfolz and Wilson, 2002). Clearly, it is not appropriate to deem an economically important species with

high ornamental value as invasive without considering all cultivars. Buddleja davidii is a widely cultivated,

extremely popular, flowering shrub with attractive foliage and a range of flower colors, some with

exceptional fragrance. A member of Loganiaceae, Buddleja is native to China and valued for summer flowering

of large inflorescences that vary in length and profusely attract butterflies. Numerous cultivars have replaced

the species. Dirr (1998) lists 70 B. davidii taxa that can be grouped by white, lanvender/blue, pink/rose/

mauve, purple/violet/magenta, and yellow flowers. Unfortunately, some of the same properties that lend it as a

great landscape plant (i.e., long flowering period, adaptability to a range of environmental conditions, ease

of propagation, and high vigor) also predispose it as a potentially invasive woody shrub. The species B. davidii

has escaped cultivation in 19 states and Puerto Rico ( and is considered a weed in

Hawaii (Staples et al., 2000), New Zealand (Kay and Smale, 1990), Australia (Csurhes and Edwards, 1998) and

Great Britain (Crawley, 1987). In the US, it is not listed as a noxious weed, however, it is considered by many

as weedy, as it is commonly found along roadsides, streamsides and other disturbed areas of its growing range.

In Florida, there are no vouchered specimens of its escape into natural areas, although it is commonly utilized

in landscapes of the north and central part of the state. Buddleja lindleyana, a separate species with darker

green leaves and longer flower panicles, has escaped cultivation in Florida ( as well as

8 other states (

Because of its invasive characteristics, extensive use in the landscape, numerous cultivars, and history as an

invasive plant in other countries, Buddleja is a good candidate to evaluate for seed production and seed

germination in Florida. Specific objectives of the full study were to (1) assess the plant growth, visual quality,

and seed production and viability of 14 Buddleja cultivars planted in west (Milton) and central/south Florida

(Fort Pierce). Partial results of the Fort Pierce study will be presented here.


Fourteen Buddleja cultivars were selected for this study based on availability, popularity, and performance in

the landscape (Table 1). Each cultivar was clonally propagated (West Florida Research and Education

Center, WFREC), transferred to 3.8 L pots, and fertilized with a slow release fertilizer prior to planting.

The experiment was conducted at Fort Pierce (USDA Zone 9B) where 9 uniform plants of each cultivar were

planted (4 June 2003) 8' on center on raised beds covered with white plastic mulch. Plants were watered by

seep irrigation as needed. Visual quality assessments (plant color, form and flower) and seed production data

(date of first visible seed pods) were taken monthly by three individuals for each cultivar in each block.

Assessment of color and form was performed on a scale from 1 to 5 where 1=very poor quality, not

acceptable, severe leaf necrosis or yellowing, 2=poor quality, not acceptable, large areas of necrosis or

yellowing, poor form, 3=fair quality, marginally acceptable, somewhat desirable form and color, 4=good quality,

very acceptable, nice color without yellowing, good form, marketable, and 5=excellent quality, very

marketable. Flowering was assessed by recording the percent of plant canopy covered with flowers on a scale from

1 to 5 where 1=no flowers present, 2=25% of canopy with flowers, 3=50% of canopy with flowers, 4=75% of

canopy with flowers, and 5=100% of canopy with flowers.

Plants were harvested after 25 weeks. After final visual quality measurements were taken, growth indices

were calculated as an average of the measured height and two widths ((height + north-south width + east-

west width)/3). Panicle infructescences were removed from shoots prior to severing plants at the crown. Seed

pods were separated from the flowers, weighed and allowed to dehisce at room temperature. Separately, shoots

and flowers (no pods) of each plant were oven dried at 70 OC for 1 week and weighed. Vegetative re-growth from

the severed base of each plant was assessed and recorded 4 months after plants were harvested.

Preliminary seed germination studies were conducted on seed collected from 6 cultivars of B. davidii

('White Profusion', 'Pink Delight', 'Dartmoor', 'Nanho Alba', 'Black Knight', and 'Nanho Purple') grown in the

Milton Botanical Gardens under open pollination. Seed was collected from plants at maturity and allowed to dehisce

at room temperature (22 to 25 OC) in paper bags for 1-2 weeks. Individual treatments for all incubator

germination experiments consisted of five replications of 25 seeds placed on two sheets of Reeve angel filter

paper (Whatman Inc., Clifton, NJ) in 9 cm petri-dishes. The filter paper was moistened with 10 mL nanopure

water containing 0.15% liquid Captan to prevent fungal growth. All dishes were sealed with Parafilm to

prevent desiccation. Germination studies were conducted in temperature and light controlled incubators

(Precision Model 818) equipped with fluorescent lamps. Seed were placed in light or darkness at 15, 24, 33

and 30/20 -C. A 12 hour photoperiod was maintained in each chamber with a photosynthetic photon flux of 22-

30 pmol.m-2.s-1. Dishes assigned to dark treatments were wrapped in two layers of heavy-duty aluminum foil

and remained unopened until the final day of the experiment. Germination of seed exposed to light was

monitored daily for 28 days. Seed germination in incubators was concurrent with seed germination in

the greenhouse. Twenty-five seeds of each species were placed in 8.9 cm pots filled with soilless germination

mix (Fafard, Inc., Apopka, FL). Two treatments were implemented whereby seeds are placed either on the

soil surface or 1 cm below the medium. Diurnal greenhouse temperatures were recorded with a Universal

K thermograph (Ryan � Instruments, Redmond, WA). A seed was considered germinated when a cotyledon

was visible above the medium.


Plant growth, visual quality, flowering and re-growth varied significantly with each cultivar (Table 2).

Buddleja davidii x lindleyana and B. x weyeriana 'Honeycomb' had the greatest growth index and shoot dry weight

of all cultivars. At 8 weeks, 'Dartmoor' had the highest flower rating, with almost 75% of the shoot canopy

having open flower panicles or buds. Each of the 14 cultivars evaluated produced seed. The shape and number

of seed pods per infructescence varied with cultivar (data not shown). For example, on average, a single plant

of 'White Profusion' (2.5' tall) produced 13.6 g of seed, each pod containing approximately 52 seeds; whereas,

a single plant of 'Nanho Blue' (1.9' tall) produced 5.01 g of seed, each pod containing approximately 82 seeds.

Large differences in the amount of viable seed have been reported for other B. davidii cultivars. As part of a

variety trial including 50 Buddleja taxa at Longwood Gardens (Kennett Square, PA), Anisko and Im (2001)

reported that only two ('Orchid Beauty' and 'Summer Rose') out of the 35 B. davidii cultivars tested produced

less than 0.1 gm of seed per infructescence. Visual quality ratings (foliage color and plant form) were highest

for 'Dartmoor', 'Honeycomb' and B. davidii x lindleyana, indicating that even at the end of the season, plants were

of good quality and marketable. All cultivars had some vegetative re-growth from the severed crown of the

original plants, with the exception of 'Nanho Purple'. Highest re-growth (56%) occurred for 'Moonlight'.

Regardless of temperature or cultivar, light was required for germination (data not presented). This suggests that

in natural conditions, seeds may not germinate if shaded by liter or a leaf canopy or following burial in soil. With

or without light, less than 2% germination occurred at 33 OC for each cultivar (data not presented). At 15 or 24 �C

in light, germination was greatest for 'Nanho Purple' followed by 'Dartmoor' (Figure 1). Germination of 'Black

Knight' and 'White Profusion' was consistently lower than that of other cultivars, regardless of temperature.

The results from these studies suggest that invasive properties of Buddleja may differ greatly among cultivars.

While long flowering periods, prolific seed production, lack of seed dormancy, and aggressive growth don't

constitute a plant as invasive, it does merit caution when utilizing this species in the Florida landscape and it

does support the need for suitable sterile alternatives.


Authors gratefully acknowledge the Florida Department of Environmental Protection for funding the initial

germination research on B. davidii and B. lindleyana and the University of Florida - IFAS Invasive Plant

Working Group for funding the cultivar evaluation study.


Anisko, T. and U. Im. 2001. Beware of butterfly bush. American Nurseryman July, 46-49.

Crawley, M.J. 1987. What makes a community invasible? In A.J Gray, M.J. Crawley, and P.J. Edwards

(ed.) Colonisation, Succession and Stability. Blackwell Scientific Publications, London.

Csurches, S. and R. Edwards. 1998. Potential Environmental Weeds in Australia: Candidate species for

preventative control. Biodiversity Group, Canberra ACT.

Dirr. M.A. 1998. Manual of Woody Landscape Plants. Stipes Publishing, L.L.C., Champaign, IL.

Hodges, A.W. and J.J. Haydu. 2002. Economic Impacts of the Floriculture Environmental Horticulture Industry,

2000. Economic Information Report El 02-3, University of Florida, Gainesville, FL.

Kay, M. and M.C. Smale. 1990. The potential for biological control of Buddleja davidii Franchet in New Zealand.

Forest Research Institute, Rotorus, New Zealand. Pp. 29-33.

Krumfolz, L.A. and S.B. Wilson. 2002. Varying Growth and Sexual Reproduction across Cultivars of

Ruell//ia brittoniana. Proc. Southern Nursery Assoc. 47:99-103.

Reichard S.H. and C.W. Hamilton. 1997. Predicting invasions of woody plants introduced into North

America. Conserv. Biol. 11:193-203.

Staples, G.W., D. Herbst, and C.T. Imada. 2000. Survey of invasive or potentially invasive cultivated plants

in Hawai'i. Bishop Museum Press, Honolulu.


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