University of Florida

Hymenachne: Introduction

West Indian Marsh Grass, Hymenachne amplexicaulis (Rudge) Nees, (hereafter referred as Hymenachne) is invading wetland marshes and flood plains in central and south Florida. Hymenachne is a native of South America and the West Indies and has spread to most countries of the neo-tropics. The pathway and timing of the introduction of this grass into Florida are uncertain; however, the first herbarium record was from a ponded pasture in Palm Beach County in 1957.  Current records confirm that Hymenachne is present in wetlands and rivers in 16 counties in Florida.  Dispersal and establishment of Hymenachne in central and south Florida is favored by its adaptation to high levels of water, summer floods, and high nutrient content in the water.

An exotic insect accidentally introduced into Florida from South America, Ischnodemus variegatus (Signoret) (Hemiptera: Blissidae), feeds on Hymenachne at all locations where the plant is found in Florida.  Research indicates that the insect feeds almost exclusively on Hymenachne.  Research in Myakka River State Park has shown that the density of I. variegatus is typically too low to cause substantial damage to Hymenachne, although occasional outbreaks occur which visibly reduce plant vigor.  Any chemical strategies developed to manage Hymenachne should attempt to minimize negative effects to I. variegatus

Previous Activities

  • Temperature-dependent development of Ischnodemus variegatus
  • Host specificity testing of Ischnodemus variegatus
  • Impact of Ischnodemus variegatus to Hymenachne amplexicaulis


Hymanchne

Ischnodemus variegatus

Seed stalk