Invasive plant species of Paies Palikir Pohnpei

A few years ago I realized that pictures from fall 2007 that I had thought were of Melastoma malabathricum var. marianum were actually the then recently identified invasive Clidemia hirta. M. malabathricum is a plant known locally as pisetikmei and has local medicinal uses. I realized that being able to identify and distinguish invasive species from locally useful and culturally important species was relevant to an ethnobotany class. I was also aware of the confusion that had occurred a over a decade earlier involved the introduction of Piper auritum, known also as false sakau, which some on island thought was a giant variant of Piper methysticum.

Dissotis rotundifolia. Melastomataceae. Also known as Spanish shawl, Pink lady, trailing dissotis. May also be known as trailing Tibouchina.

The current proposed course outline includes the student learning outcome: students will be able to identify, distinguish, and remove invasive plant species based on field experiences during which students identify invasive species. The walk on Tuesday November first specifically targeted this learning outcome. Invasives are identified as they are encountered throughout the term, this exercise however has a singular focus on invasive plant species.

April, Natasha, and Georgene surrounded by Ischaemum polystachyum

The role of invasive plants as threats to native and endemic plants was clarified in a 15 July 2016 paper, Alien plant invasions and native plant extinctions: a six-threshold framework by Paul O. Downey and David M. Richardson, published in AoB Plants and reported on by the AAAS as The 6 steps to extinction. For the class this term, I printed out the article and a list of the invasives I hoped to find in our field walk.

The walk went well. Paies, Palikir never fails to produce the best collection of invasive species. The students carried their handout with them. Invasive species is a complex topic. Some plants, such as Clidemia hirta, are simply threats without redeeming value. Other invasives are useful. Falcataria moluccana also known as Moluccan Albizia is a nitrogen fixing tree that sakau (Piper methysticum) grows well under and is a lead fuel wood tree. F. moluccana burns green and is the choice fire wood on the island. Without this invasive tree, native and endemic trees would be cut down for firewood. F. moluccana grows fast and drops limbs regularly, providing a ready supply of firewood without one needing to even cut the tree down. And the tree does not deplete the soil. Thus the role of invasives can be complicated.

Then there are plants that are considered invasives elsewhere, but are important medicinal plants on Pohnpei, such as Clerodendrum inerme. Clerodendrum inerme is a key plant in local sauna steam bath treatments and is used as a medicine to ease congestion of the lungs due to a viral chest cold.

Other potential invasives such as Pterocarpus indicus are not aggressively invasive in the climate of Pohnpei. Other plants are. During the walk and talk I cover these aspects of invasive plants while identifying them in the field. A recently bulldozed area of the college campus provides an excellent field laboratory of the first plants to colonize new territory - and every single one was an invasive plant. The new article by Downey and Richardson also makes clear that the time scale on which invasives may act is far longer than realized. This casts a long shadow over the native and endemic plants of Pohnpei and the rest of Micronesia.

The following is the check list provided to the students. The list is by no means exhaustive, this is a list of some of the more commonly seen invasives in Paies, Palikir, Pohnpei. Most of these plants were observed on this particular walk:

__ Acacia auriculiformis: a tree that can spread by suckers
__ Ageratum conyzoides. Pwisehn kou (cow dung weed). Considered useful.
__ Allamanda cathartica var “Hendersonii” Angle's trumpet
__ Bidens alba: Beggar's tick.
__ Chromolaena odorata. Pohnpeian: wisolmat.  Global in distribution. Locally known as wisin mat en rere. Possibly came in on a tractor, maybe in dirt in its treads, spread around the island when the road was bulldozed.
__ Clerodendrum paniculatum. Chinese pagoda flower shrub.
__ Clerodendrum quadriloculare. Shade tolerant. Aggressive. Possibly allelopathic.
__ Clidemia hirta. Riahpen roat. Shade tolerant. Aggressive. Studies suggest allelopathic. Do not confuse with Melastoma malabathricum var. marianum.
__ Commelina diffusa, a member of the wandering jew family.
__ Chromolaena odorata. Siam weed. wisolmat en rehnwel.
__ Cheilocostus speciosus (Costus speciosus) crêpe ginger. Shade tolerant.
__ Dissotis rotundifolia. Melastomataceae. Also known as Spanish shawl, Pinklady, trailing dissotis. May also be known as trailing Tibouchina.
__ Falcataria moluccana. Moluccan Albizia. Nitrogen fixing, fuel wood tree. Useful.
__ Hippobroma longiflora Star of Bethlehem. Invasive. Toxic.
__ Ipomoea carnea. Bush morning glory. Toxic.
__ Ischaemum polystachyum: Reh padil. Invasive grass introduced by Japanese as feed for asian oxen.
__ Leucaena leucocephala. Dangan-dangan. Highly invasive on Saipan, less so here.
__ Melastoma malabathricum var. marianum: A native plant. Potentially invasive but useful. Pisetikimei.
__ Merremia peltata. iohl, puhlah.  A sign of a lazy farmer?
__ Mimosa pudica. Sensitive plant. Invasive. Worse: Mimosa invisa. The later forms impenetrable thorn thickets.
__ Pterocarpus indicus. Narra. Rosewood. Not invasive on Pohnpei.
__ Nymphaea spp. Water lily. Potentially highly invasive of fresh waterways.
__ Pennisetum purpureum: Elephant grass. brought in by the Japanese who mistakenly believed cattle would eat it.
__ Spathodea campanulata: African tulip tree. Birds spread the seeds. Very aggressive tree. Hard to kill.
__ Sphagneticola trilobata (Wedelia trilobata): brought from Hawaii by women down at the Catholic mission around 1970 who thought it would look nice in their gardens. All over the island now. Possibly allelopathic. Singapore daisy.