To Be, or Not to Be, a Weed
This month we are looking at plants that are endangered but could be mistaken for “weeds.” Both appearance and/or behavior can account for misconceptions and perceptions. What happens when there are plants that display weed-like characteristics, yet aren’t weeds? What happens when those plants are also endangered? How do we address the perception of “weed” to obtain and maintain protection status? If a plant is thought of as a weed, how do you convince anyone of the need to preserve it? The answer? It’s complicated. These questions are the subject of larger, and complex, debates.
James Lange of Fairchild Botanic Garden states that you can separate these plants into categories of “weedy” behavior, and “weedy” appearance.
“The Tephrosia spp. is a very aggressive prostrate vine. The Chromolaena frustrata and Ageratum maritimum are considered garden weeds and disturbance species. The Dalea carthagenensis is viewed as a weed throughout South and Central America. And they all have in common that they are rare plants and actually thrive in marginal habitats in terms of weedy potential.
“There are a number of rare species that absolutely thrive in mowed areas, and traffic right-of-ways, but are extremely rare in natural habitats, making for complicated conservation decisions.
“In Florida, a state-endangered liana, hoopvine (Trichostigma octandra) sometimes reaches nuisance levels in preserves where it is found. It weighs down the canopy and shades the understory. Managers are faced with the dilemma of maintaining habitat while preserving the existence of this rare species.”
Another example of “weedy” behavior would be Ambrosia linearis, a plant in the Center for Plant Conservation National Collection that fits the profile of a rare species that can sometimes behave as a weed. Jim Locklear of Lauritzen Gardens notes that Ambrosia linearis “is a G3 species that is endemic to the plains of eastern Colorado. It occurs naturally around the outer margins of playas, which are temporarily flooded lakes that occur in grasslands. It also occurs along upper terraces of intermittent streams in the region. Ambrosia linearis can also occur in dense stands in roadside ditches and along gravel roads in the area. It appears the plant spreads into these areas when roads have bisected its natural habitat. It is not a problem in these areas, and actually probably helps prevent erosion along roadsides. These roadside populations are most likely not controlled as they seem to be confined to ditches and occur in rural, very sparsely populated areas. However, routine road maintenance activities such as periodic grading of the road bed could have a negative impact. The greater challenge could come in trying to encourage preservation of high-quality occurrences in natural habitat when the plant can also grow as a roadside weed.
“Fortunately, playas are recognized as unique landscape features in the Great Plains and of high conservation value because of their importance to migrating shorebirds and waterfowl. The unique association of Ambrosia linearis with playa habitat just adds to the importance of preservation.”
According to James Lange, “there are rare plants that may have a “weedy” appearance that could make it difficult to push for protection. Several of our true endemics are diminutive plants with the reproductive potential of weeds but are true habitat specialists. Chamaesyce spp., Poinsettia pinetorum, Tragia saxicola come to mind but there are several others. This makes sense given that in order to evolve in the brief period of geologic time South Florida has been around you’d have to reproduce a lot.
“These species can be a tough sell from a conservation standpoint because they are non-charismatic, weedy-looking things. For example, Two-Spike Crabgrass (Digitaria pauciflora) which fits in this category, just by its nature of being a crabgrass, but, again, a true habitat specialist.”
The Tale of a True Habitat Specialist
“Long ago, one rebellious sister in the crabgrass genus decided to quit her weedy ways. She diverged from more than 200 other Digitaria species (congeners), settled in a remote Florida swamp and traded her hardiness for beauty. She grew tall and acquired a bluish sheen. Her new growth sported soft, fuzzy hair; her old growth, a distinctive zig-zag, checkered pattern. She became so attractive that she didn’t feel the need to produce as many flowers. Because she loved the swamp so much, she never bothered to venture out to other lands, even though human alteration of natural water levels has recently given her much cause for concern.” Jennifer Possley, Fairchild Tropical Botanic Garden Virtual Herbarium