By Lawrence Rozas, Photo credit Larry Allain.
This is the first installment of articles to feature invasive plants of Louisiana. My goals for writing on this topic are to: (1) help readers identify Louisiana invasive plants, (2) convince readers to avoid purchasing those plants still available in the nursery trade and using them in their landscapes, and (3) encourage readers to eliminate those invasive plants already established on their property.
Invasive plants are defined as are non-native species (i.e., did not occur in the U.S. before European settlement) that cause environmental damage and economic harm where they have been introduced. They cause environmental harm by spreading uncontrollably and replacing native species, upon which native wildlife depends. Invasive species also take a great toll on our economy by the damage they cause to agricultural crops, fisheries, forests, and native wildlife as well as the high cost required to monitor and manage the problems they cause.
Yellow Flag Iris is a native of Europe and was introduced into the U.S. as an ornamental. This Iris is classified by the Louisiana Department of Wildlife and Fisheries as a Tier I invasive species defined as “currently causing severe or widespread negative impacts on wildlife or natural communities in Louisiana”. It has infested a variety of wetland habitats in the state including swamps, and the edges of lakes, ponds, and bayous. Its ability to withstand droughts and extended anoxic conditions gives this species a competitive advantage over many native wetland plants. Yellow Flag Iris spreads by rhizomes and seeds; it forms large clonal colonies that replace native species including native irises; and the plant contains glycosides, which are toxic to grazing animals.
Unfortunately, it continues to be sold in the nursery trade because Yellow Flag Iris is admired for its quick establishment, evergreen foliage, and vigorous growth. This invasive species can be distinguished from native Louisiana Irises by the presence of a central vein in the leaf of the Yellow Flag Iris; native irises lack a central vein.
Responsible gardeners have several wetland-adapted native species from which to select that are a better choice for landscaping their property. Each of the following native species name is linked to pictures and more information available at the “Plants of Louisiana” website supported by the U.S. Geological Survey. Louisiana is blessed with at least six species of native irises from which to choose as a substitute for Yellow Flag Iris. If you are looking for a vigorous iris with tall evergreen foliage, the large Giant Blue Iris Iris giganticaerulea is for you.
Iris giganticaerulea, giant blue iris Photo credit Larry Allain This iris has a very large (largest flower of the Louisiana irises), light blue to lavender to purple flower, sometimes white to yellowish-white, but generally with a blue to purple color. The sepals are widely spreading, arching downward. The signal is a rich yellow, with a yellow-orange stripe along the pubescent central rib. The bright green leaves are stiff and erect, arising from shallowly rooted, branching rhizomes that can form large colonies. Iris giganticaerulea is commonly found growing in shallow water in wet meadows, marshes, wet ditches, and bogs. The giant blue iris grows 3-6 feet tall and prefers freshwater habitats.
Other Louisiana irises include the Zigzag I. brevicaulis, Copper I. fulva, Dixie I. hexagona, and Abbeville Red I. nelsonii. Two other wetland plants, Swamp Lily Crinum americanum and Spider Lily Hymenocallis lireosme, would also be fine replacements for the invasive Yellow Flag Iris. |
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