Sixteen new weeds in Guam have been identified and documented in an internally published report by the University of Guam botanist and assistant professor Dr. Wei Xiao of the UOG College of Natural & Applied Sciences and her students,

Xiao said the report will be useful for botanists as well as homeowners, landscapers, gardeners, farmers, and other residents who may be afflicted by weeds, otherwise defined as plants acting as pests.

In garden and agriculture settings, weeds compete with other plants for resources and can ultimately reduce a crop’s yield. They can also bring different insects and diseases to the field that can affect crop quality.

“The first and most important thing is to know what you are dealing with before you look into how to manage it,” Xiao said.

Xiao holds a doctorate in plant biology and who also serves as curator of the UOG Herbarium, has been keeping a list of plants in urban environments in Guam that she has not seen before.

She identified each plant species through her personal expertise and that of colleagues who are knowledgeable in certain taxa.

This past semester, she tasked her Plant Systematics class with looking for the plants in Guam and Micronesia botanical literature dating back to the 1970 publication “Flora of Guam” by Benjamin C. Stone, which Xiao said is the most comprehensive listing of regional plant species to date.

The students found that 16 of the suspected plants were, in fact, undocumented. By their common names, they are:

Purple justicia
Hairyflower wild petunia (violet ruellia)
Prostrated ruellia
Popping pod
Latok
Creeping indigo
Caribbean stylo
Purple cleome
Ivy-leaved morning glory (mile-a-minute vine)
Turtle vine
Brittle false pimpernel
Bloodgrass
Shrubby false buttonweed
Basil buttonweed
White snakeweed
Chinese grape vine

Few studies over the last two decades have updated exotic plant species in Guam with a recent publication on weeds being a 2006 book “Color Atlas of Common Weeds of Guam” by James McConnell and Lauren Gutierrez.

“We are confident that the majority of species on our list are new [to the island] based on their record on Guam and their spreading history,” Xiao added.

Xiao said that many of these new weeds have a pan-tropical distribution, so it is not surprising that they eventually arrived in Guam.

But she also found that a few of the more aggressive new weeds are only common in the southern United States, which is important to know in examining how they got to Guam and measures that might help prevent new arrivals in future.

“We will need to keep an eye on them to see if they harm native forests or cause troubles in agriculture,” she said.

The report on the newly documented weeds as well as fact sheets on some of these species can be viewed here.