Hymenachne amplexicaulis

Common Name: West Indian marsh grass

Family: Poaceae

Common Synonyms: Hymenachne acutigluma

USDA Hardiness Zone: 8b-10b

Growth Habit: Aquatic, emergent graminoid

Origin: Central America, Mexico, and South America

FISC Category: 1

FDACS Listed Noxious Weed: No

Introduction Date: Earliest Florida herbarium specimen from 1957

IFAS Assessment:

• North: INVASIVE
• Central: INVASIVE
• South: INVASIVE

Description

Robust wetland grass ascending to 1 m tall, rooting at the lower nodes. Stems are floating, creeping or ascending. Stems are filled with a white pith (not hollow), unlike most other grasses. Leaf blades are flat, to 35 cm long, cordate at the base and often clasping the stem. Inflorescence a dense terminal panicle.

Habitat

Invades marshes, river edges and wet pastures

Comments

The non-native Myakka bug (Ischnodemus variegatus) was observed feeding on West Indian marsh grass, and acts as a biological control agent. Similar in appearance to native maidencane (Panicum hemitomum).

Control Methods

• Manual: Mechanical: Manipulation of water levels (drying, drowning plants).
• Chemical: Foliar (96 fl oz/ac/year aquatic imazapyr). Imazapyr provides best control 9-12 months after treatment under dry and flooded conditions. However, repeat treatments when dry should include glyphosate (2% glyphosate+ 0.5% imazapyr). [IFAS]
• Biological: Ischnodemus variegatus (Myakka bug), was observed feeding on West Indian marsh grass. A non-native Blissid true bug (Insecta: Hemiptera) greatly prefers this host plant relative to a few other native plants. [IFAS, http://edis.ifas.ufl.edu/in491]

Control Notes

This species readily grows from seeds and small vegetative pieces. Retreat before flowering to prevent the introduction of additional seeds to the seed bank.

References

Plant Conservation Alliance, Alien Plant Working Group. West Indian Marsh Grass: Least Wanted. Www.nps.gov/plants/alien/fact/hyam1.htm. Viewed on 26 August 2015.

http://plants.ifas.ufl.edu/wp-content/uploads/files/caip/SP257/Hymenachne_amplexicaulis(SP257-034).pdf

IFAS. 2011. Integrated Management of Nonnative Plants in Natural Areas of Florida. http://edis.ifas.ufl.edu/pdffiles/WG/WG20900.pdf Accessed June 13 2017.