|Ruellia is the second largest genus in the Acanthaceae and is found in a wide range of habitats including high to low elevation rain forests, dry deciduous forests, savannas, grasslands, deserts, and swamps.|
Invasive species are ubiquitous throughout our current landscape. An invasive species is one that has not only naturalized outside its native geographic range but has out-competed native species to a degree that leads to their displacement or eradication. Whether it be mussels clogging the intakes of ballast tanks in the Great Lakes, turtles displacing natives species in the fresh water ecosystems of North America, Asian Wooly Adeldigs destroying the great hemlock forests of The East, or annual weeds that change habitat fire regimes, invasive species negatively affect health of humans and the ecosystems that we inhabit. To better understand the threats that invasive species pose, it is important that we identify their distribution and abundance, as a starting point to containment and remediation strategies.
A Summary from Beautés fetales: Acanthaceae species as invasive alien plants on tropical Indo-Pacific Islands
The Acanthacaeae, having a mostly tropical distribution, contains some number of species with varying degrees of invasiveness around the world, particularly on and around islands. Though Acanthaceae are not typically thought of as the tenacious invaders that some members of Poaceae, Rosaceae and Fabaceae are, their use in ornamental horticulture is widespread throughout the tropics and has resulted in artificially expanded ranges of many species. Some of these range expansions have lead to unanticipated problems of invasive or potentially invasive ornamentals. In addition to (or instead of) sexual reproduction through fertilization and seed development, many Acanths that have become invasive are also capable of self-propagation through asexual means such as stem fragmentation or adventitious shoot formation. This mode of reproduction, which obviously lacks a need for a pollinator, is perhaps most dangerous in foreign landscapes because of the plant's ability to self-propagate in the absence of pollinators. Disturbed areas such as roadsides, cleared forests, and housing developments provide prime habitat for invasive species, where they can often grow with little competition once they are introduced to the location by humans. Odontonema strictum provides one such example. This shrub, native to Central America, was originally planted in Tahiti as an indicator for road crossings but has since spread into neighboring cloud forests in extremely dense patches. Beyond the original, intended introduction, invasive species can be further dispersed by humans through plant adherence to shoes or cloth, vehicles or boats that contain garden or plant debris, or by irrigation canals and waterways. In the Indo-Pacific islands alone, 52 species of Acanths are of non-native origin, many of which have become naturalized, potentially invasive, or invasive.
Below is a listing of the article’s eight most invasive Acanthaceae species on tropical islands throughout the world. Also included is a list of eight species that have the potential to become invasive on tropical islands, based upon their life history traits. The maps depicting each species have a rough approximation of the native distribution highlighted in blue and the non-native distribution highlighted in red. Species that are potentially invasive are highlighted in yellow. As the authors of the article mention, this list is not to be interpreted as exhaustive or complete, but signifies 16 cases of invasive acanths that should be monitored carefully in their alien habitats.
Jean-Yves Meyer and Christophe Lavergne. Beautés fetales: Acanthaceae species as invasive alien plants on tropical Indo-Pacific Islands. Diversity and Distributions. 10. 2004. 333-347.