Taxonomic name: Ischaemum polystachyum J. Presl
Synonyms: Andropogon mariannae Steud., Andropogon paniceus Steud., Ischaemum chordatum (Trin.) Hack. ex Warb., Ischaemum digitatum Brongn., Ischaemum digitatum var. polystachyum (J. Presl) Hack, Ischaemum intermedium Brongn., Spodiopogon chordatum Trin.
Common names: mah (Kosrae), paddle grass (English), reh padil (Pohnpei)
Organism type: grass
Considered to be native to many Pacific Islands, Ischaemum polystachyum (paddle grass) is apparently one of few plants to become a native invasive. In Pohnpei (Federated States of Micronesia) it is considered a particularly aggressive plant and is very abundant on other Islands of it's native range. Paddle grass mainly inhabits roadsides, garden clearings and grasslands.
Sprawling grass, with long decumbent culms finally ascending to a little more than a metre in height.; pubescence of nodes, sheaths and blades variable; racemes 4-7 (or more), about 8cm long, spreading; rachis joints and pedicels trigonous, the angle scabrous or short-ciliate, about 4mm long, bowed equally away from each other; fertile lemma of sessile spikelet bearing a twisted geniculate awn, (Henty, 1969, in PIER, 2002). Tends to be gregarious, (Henty, 1969).
Ischaemum timorense, Ischaemum tropicum
In New Guinea Ischaemum polystachyum grows on roadsides. It is also present in garden clearings and grasslands from sea level to 2,000m, (Henty, 1969, in PIER, 2002). In New Guinea, in the Eastern highlands, it forms dense stands in wet gullies, (Henty, 1969).
Forms dense swards, which tend to exclude other species. (Waterhouse, pers.comm. 16 March 2003)
In New Guinea the Asaro people were reported to plant paddle grass to control soil movement on slopes, (Henty, 1969).
Although this is a native grass, it is very abundant along roadsides and in disturbed areas. It is particularly aggressive on Pohnpei. (PIER, 2002)
Native range: Philippines to New Guinea and Polynesia.
Known introduced range: Commonwealth of the Northern Mariana Islands, Federated States of Micronesia (Kosrae, Pohnpei, Yap, Caroline outer islands (Ifaluk)), Guam, Palau (Babeldaob, Koror, Ngerkebesang, Malakal, Aulupse'el), Papua New Guinea, and Philippines. - native all locations.Torres Strait Islands (Australia) Ischaemum polystachyum has not reached the Australian mainland (Waterhouse, pers. comm, 2003).
Introduction pathways to new locations
Agriculture: Introduced to Pohnpei, Micronesia as cattle fodder. (College of Micronesia, 1999)
Translocation of machinery/equipment: Introduced sometimes with translocation of machinery.
Transportation of domesticated animals: Introduced sometimes with translocation of livestock.
Transportation of habitat material: Introduced sometimes with translocation of produce.
Local dispersal methods
Natural dispersal (local): Self spreading by seeds. (PIER, 2002) and vegetative fragments.(Waterhouse, pers. comm, 2003).
On animals: Introduced sometimes with translocation of livestock.
Translocation of machinery/equipment (local): Introduced sometimes with translocation of machinery.
Preventative measures: A Risk assessment of
Ischaemum polystachyum for the Pacific region was prepared by Pacific Island Ecosystems at Risk (PIER)
using the Australian risk assessment system (Pheloung, 1995). The result is a score of 20 and a recommendation of: reject the plant for import (Australia) or
species likely to be a pest (Pacific).
Reproduction occurs by seed. (PIER, 2002). Culms also root at nodes. Vegetative reproduction is probably also important (Waterhouse, pers. comm, 2003)
Reviewed by: Barbara Waterhouse. Botanist, Australian Quarantine and Inspection Service and Cooperative Research Centre for Australian Weed Management. Australia.
Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Thursday, 26 January 2006