How Did We Get Here: A Very
Brief Introduction to Invasive
Ornamental Plants
SARAH REICHARD, PH.D.
UNIVERSITY OF WASHINGTON BOTANIC
GARDENS
REICHARD@UW.EDU
Outline
 The Dilemma
 Codes of Conduct to facilitate discussion
 Cultivar sterility
 Differences and similarities in outlooks and
preferences between ecologists and horticulturists
“The greatest service which can be
rendered any country is
to add a useful plant
to its culture”
…Secretary of State, Thomas Jefferson 1790
US should facilitate the entry of “plants
of whatever nature whether useful as food
for man or the domestic animals, or for
purposes connected with the manufactures
or any of the useful arts”
…President John Quincy Adams 1827
Desirable Traits for Ornamentals
 Long flowering/fruiting periods
 Early flowering in the life cycle
 High Fruit/Seed Production
 Easy propagation
 Vegetative spread/ground cover
 Pest resistance
 Drought resistance
 Hardy rootstock
Traits Associated with Invasive Plants
 Long flowering/fruiting periods
 High Fruit/Seed Production
 Early reproduction in the life cycle
 Seed germination easy
 Vegetative spread
 Pest resistance
 Drought resistance
 Coppices/recovers from disturbance easily
Woody Plant Introductions
North America – 235 species
Accidental
1%
Erosion Control
3%
Agriculture
14%
Landscape
Horticulture
82%
Overall: ~ 65% of invasive plants introduced for horticulture
So…
Horticulturists, by introducing plants, were simply
doing what our culture has told them for centuries
was a good thing
They are selecting plants that have traits that
gardeners desire, providing jobs
Now they are all being told something different –
that by introducing plants that become invasive,
they are bad – values are changing
Five Stages of Grief
E. Kübler-Ross (1969)
Five Stages of Grief
E. Kübler-Ross (1969)
 Denial
“You don’t know what you are talking about – I can
hardly get the plant to grow in my garden. And it
never seeds there”
“Biodiversity is higher in invaded areas”
Five Stages of Grief
 Denial
 Anger
“You are all a bunch of xenophobic Nazis. You only
want us to grow native plants”
Ecologists vs. Horticulturists
Codes of Conduct
 Voluntary rules of behavior that a group of people
agree to observe
 Set standards for professions, but also for amateurs
Codes of Conduct
The St. Louis Declaration
 Nursery professionals
 Botanical gardens and arboreta
 Gardening public
 Landscape architects
 Government – state and federal
http://www.centerforplantconservation.org/invasives/
Findings (Values)
 People are the major dispersers of plants and the
current magnitude of dispersal is unprecedented
 Plant introduction and improvement brings
diversity to food, landscapes, and medicine
 A small proportion of introduced species become
invasive and have unwanted impacts
 Species invasions can be regional in nature, but the
impacts may be far removed from the site of
introduction
Guiding Principles
 Plant introduction should be done in a way that
minimizes harm
 Efforts must be national in scope, but with a
regional perspective
 Prevention and early detection are important
 Professional training and education are essential
 Solutions must include broad-based teams
 All tools, esp. codes of conduct are important
Codes of Conduct
Nursery Owners
1.
2.
3.
4.
5.
6.
Ensure that invasive potential of new
introductions is assessed
Identify suitable alternatives to invasives
Develop and promote alternatives
Phase out existing stock of agreed-upon invasive
species
Follow all laws across political boundaries
Encourage customers to use and garden writers
to promote non-invasive plants
Botanical Garden Codes of Conduct
 First, do no harm to plant diversity and natural





areas
Perform risk assessments for introductions
Remove invasives from plant collections
Develop non-invasive alternatives to invasive plant
material
Educate the public
Follow all laws and quarantines
California Horticultural Invasives Prevention
Creating Opportunities for Dialogue
Photos by Angel Guerzon
Five Stages of Grief
 Denial
 Anger
 Bargaining
“I can just cut the seed heads off before they
disperse”
“Alright, pampas grass/butterfly bush/ivy is
invasive, but these new cultivars won’t invade”
Cultivar Sterility
“Cultivars per se do not invade: their offspring
invade”
Knight, T.M., K. Havens and P. Vitt. BioScience. 2011
Sterility in Plants
 Natural or induced mutations may reduce sterility,
common and evolved many times
- male sterility – no or reduced pollen
- Can still produce seeds if other pollen is available
Sterility in Plants
 Female sterility – no or reduced ovules, death of
pistil tissue prior to pollination
 Relatively rare – Oleaceae, Saxifraga, Ulmus
Hybridization
 Very common in plants
 Many species are the result of hybridization
 Polyploids (higher than diploid) are very common (~
up to 70%)
 Some species may have both
diploid and polyploid individuals
Hybridization – Triploids
 Triploids mostly sterile
 Can still produce fruit
 Some can still reproduce
asexually (many dandelions
are triploid)
Hybridization – Triploids
Knight et al. Main Points
 Claims of fecundity are often not well substantiated
 Offspring of cultivars may behave differently
 When crossed with other cultivars, could become
fertile
 Even large reductions in fecundity can result in
population increases in long-lived plants
Five Stages of Grief
 Denial
 Anger
 Bargaining
 Depression
 Acceptance
Stakeholder Survey
 1801 completed surveys
 5 U.S. states and 4 Canadian provinces
Ransom-Hodges, A. 2007. MS thesis, Simon Fraser University
Stakeholder Survey
Policy Options
Policy
Enforcement
A
List and ban all species known to have become Mandatory
invasive
B
Screen and ban species with a high likelihood
of invasion
Mandatory
C
Screen and ban species with a high likelihood
of invasion
Voluntary
D
Screen and have a variable tax on introduction Mandatory
C
Fixed environmental fee
Mandatory
Barbier, Knowler, Gwatipedza, Reichard, and Ransom-Hodges, 2013,
BioScience
Policy Preferences
Summary
 Introducing plants that are useful is a long-standing




practice
Recognition of the environmental problems are more
recent and should be communicated clearly and
without emotion
Codes of Conduct provide such an opportunity
Finding suitable alternatives to invasives may
include sterile cultivars, but should include much
caution
Horticulturists lag in their understanding of the
extent of the issues, but understand that action is
needed