Ground legumes & weediness

December 2000. Palau asked which if any of the following legumes are invasive and potential weeds. Two legumes were being considered species of legumes being considered for revegetation along roadside cuts and fills along 53 miles of road being constructed on Palau’s main island, Babeldaob.

The plants are as follows:

Centrosema pubescens cv. Cardillo (centro)
Macroptilium atropurpureum (siratro)
Stylosanthes hamata (stylo)
Stylosanthes gui(y)anensis (stylo)
Aeschynomene villosa

CSIRO scientists thought that the first four could become weedy, and the last one, A villosa, might be less so. However, it was pointed out by SPC that Centrosema pubescens, (centro) and Stylosanthes guianensis (common stylo) are already present on Babeldaob, but have failed to become widely established.

Pueraria & Calopogonium

January 2001. Some comments were received from the Department of Natural Resources, Queensland, about two ground legumes, Pueraria and Calopogonium, and their weediness status.

A Weed Risk Assessment on these two species was carried out using the Australian WRA system and literature found in an hour Internet search. Both species have ‘weedy’ histories in similar environments and I assessed the species for PNG using my knowledge of climate, etc.

Pueraria (kudzu) is a well known invasive plant in the US, but has not become as serious a problem elsewhere. I think it needs a cold/hot climate. In Queensland, it is present, even widespread, but has not really become a risk. The climate may be more suitable in the highlands of PNG as there is a cold season.

It is possible for Pueraria to suffer from annual fires and a fungus; these factors may limit its spread, as they appear to have done in the Torres Strait islands, where it has not expanded over the past 10 years. This may also be the case in lowlands PNG. The literature suggests that the species can be controlled by herbicides. It is good for cattle grazing.

Nevertheless, its weediness overseas and rampant growth result in a score of 8 or 9 in a system where 6 results in the species being rejected. Obviously, climate is very variable in PNG, so this prediction used the highest risk categories. It was considered that Pueraria had the potential to become a weed.

Calopogonium mucunoides is also found in Australia; in the Norther Territory is it considered to be invasive. It is also widespread throughout the Pacific, Micronesia and parts of SE Asia from its origins in tropical America. On the Internet, there was little information on seed dispersal and without this information the species was given a score of 7, again a reject score.

However, it was not certain that this species would spread very quickly and it doesn’t have the vegetative reproduction of kudzu, so it is possibly a lower risk. Information on seed dispersal would most probably move the species into a different category, but with a weedy history it is unlikely that the species would be accepted into Australia if it was a new import.

Some notes were given on the distribution of kudzu in the Pacific islands, taken from WA Whistler (1983) Weed Handbook of Western Polynesia. It seems it was an intentional aboriginal introduction to many parts of Polynesia in pre-European times for its edible root used as a famine food.