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How does a plant in the Plant Finder get marked as “Locally Invasive Species”?
To get a “Locally Invasive Species” warning a plant has to meet some rather high criteria. Our primary source for this is the Missouri Botanical Garden’s Missouri Exotic Pest Plants list created several years ago.
Any species in the Plant Finder that is on the Category A list (with a few exceptions, see below) gets a “Locally Invasive Species” warning. Currently, these are Lonicera (japonica, maackii and morrowii), Euonymus fortunii, Lythrum salicaria, Phalaris arundinacea, Acer ginnala (now Acer tataricum subsp. ginnala), and Rhamnus cathartica. Festuca arundinacea is on the list but this is one of our common turfgrasses. We have it in as cultivars and do not flag them. The other plants on the Category A list are weeds and are not included in the Plant Finder.
Plants in the Category B list are classified as “occasional invaders with low levels of impact”. We have, however, chosen to include tree of heaven (Ailanthus altissima), Ligustrum obtusifolium, kudzu (Pueraria lobata), multiflora rose (Rosa multiflora), and Siberian elm (Ulmus pumila) as these are not desirable garden plants for our area. Daucus carota is in the Plant Finder as the vegetable” carrot” and is not flagged. Lolium perenne and Poa pratensis are lawn grasses and not flagged.
We have not flagged any plants in Category C and Category D, which are plants on a “watch” list.
Category E is a list of “non-threatening plants”. Since the time the list was produced, however, Callery pear (Pyrus calleryana) has proven to be highly invasive (probably Category A now). It is also a weak-wooded tree that is subject to storm damage and fireblight disease. Because of these more recent observations we have chosen to flag it.
To assist gardeners who access and use our information locally, nationally and worldwide we provide a link to information on any species that is included in www.invasive.org labeled “Where is this species invasive in the US?” This provides all users of our site an easy way to check and see if a plant is listed as invasive in their area.