Title: Hymenachne amplexicaulis (Rudge) Nees

wScientific Name:

Hymenachne amplexicaulis (Rudge) Nees

Common Name:

olive hymenachne, hymenachne, West Indian marsh grass



Source & more images (via ALA)

Habitat:

Tropical and subtropical regions on dry land or floating in water up to one metre deep (Kowari Editorial Committee 1991). It is a weed of savannas, ponds with predominantly mucky soils, ditches, canal banks and sandy depressional areas (Hill 1996). Hymenachne invades wetlands, swamps and wet areas along rivers and streams (Standley & Steyermark 1958).



Distribution:



Original source via GBIF


Invasiveness Assessment

ESTABLISHMENT


1. Germination requirements? Requires alternating periods of flooding and dryness to establish and survive (Weber 2003). It is adapted to fluctuating water levels and massive regeneration by seed may occur after drought. Plants usually flower from April to June but have been observed flowering in September and there’s evidence that the plant can flower and set seeds over a longer period of time in unusually wet years (DNRM 2005).

2. Establishment requirements? Sets viable seed after flowering – the seeds germinate on damp bare ground Seeds set from late autumn to early spring (KEC 1991).

3. How much disturbance is required? Occurs in shallow waters of swamp margins and river banks (Weber 2003).

GROWTH / COMPETITIVE


4. Life form? A robust perennial grass / semi-aquatic (Wildin 1989).

5. Allelopathic properties? None described in consulted references.

6. Tolerates herb pressure? It has been established for use in ponded pastures in Central Queensland (Kibbler & Bahnisch 1999). One of the major forages of buffaloes on the flood plains east of Darwin (Wildin 1988).

7. Normal growth rate? Is a large species that can grow in deeper water than other species of the same life form giving it the potential to infest wetlands and choke streams (KEC 1991). It has the ability to smother native vegetation and form dense and extensive monospecific stands (IPIF 2005).

8. Stress tolerance to frost, drought, w/logg, sal. etc? Tolerant of drought and flood (Wildin 1988).

REPRODUCTION


9. Reproductive system? Rhizomatous and sets seed (Hill 1996).

10. Number of propagules produced? ‘Massive regeneration by seed may occur after drought’ (Weber 2003). Germination is variable – ranging from 86% to 0%. Factors affecting seed fertility are not clearly understood (Hill 1996). Prolific seed production (greater than 2000/m2) (IPIF 2005).

11. Propagule longevity? Trial work indicates that in field conditions, the seed viability is still high after more than a year. Not enough information to determine propagule longevity. Therefore score as medium.

12. Reproductive period? Species forms self-sustaining dense monocultures (Hill 1996).

13. Time to reproductive maturity? Perennial grass (Wildin 1989) – therefore assume maturity within first year

DISPERSAL


14. Number of mechanisms? Seeds are dispersed by water (Weber 2003). Possibility of natural introduction to Central America via migratory birds (Hill 1996). Migratory aquatic birds (DNRM 2005).

15. How far do they disperse? As dispersed by migratory birds (DNRM 2005)– assume that it’s very likely that some propagules will disperse greater than one kilometre.


Impact Assessment

RECREATION


1. Restrict human access? Perennial grass to 2.5 metres high. It invades waterways including drains, lagoons, creeks and rivers (Diaz et al 2003). Heavy infestations may be a major impediment to access waterways.

2. Reduce tourism? “Overseas, hymenachne forms floating mats and grass islands” (NRM 2001). Serious impact on water-based recreation.

3. Injurious to people? The plant has no physical or toxic properties that may injure humans. However ‘…the mats that the plants form create a haven for mosquitoes that are vectors of Ross River Fever and encephalitis’ (NRM 2001). Therefore score as medium.

4. Damage to cultural sites? Plant not likely to cause damage to indigenous or cultural European sites.



ABIOTIC


5. Impact flow? “Hymenachne can choke drains and small watercourses, increasing flooding by reducing the flow capacity of the drainage networks” (Diaz et al. 2003). Major impact on either surface or sub-surface flow.

6. Impact water quality? “Heavy infestations reduce the infiltration of sunlight…[and] prevents the exchange of air, which normally occurs on an open water surface. As plant material decomposes it uses oxygen causing water pollution and stagnation” (Diaz et al 2003). High effects in dissolved O2.

7.Increase soil erosion? “Hymenachne can choke drains and small watercourses, increasing flooding” (Diaz et al 2003). High potential for erosion with offsite implications



8. Reduce biomass? Density of infestations suggests biomass would significantly increase. (Cruz & Salazar 1989). In aquatic situations, increase in biomass is a negative attribute.

9. Change fire regime? Occurs in wetland situations (NRM 2001). Unlikely to contribute to fire risk.

COMMUNITY HABITAT


10(a) Impact on composition of high value EVC? EVC=Swamp scrub (E); CMA=Corangamite; Bioregion=Victorian Volcanic Plain; CLIMATE=M. “Hymenachne can form pure stands that replace native wetland plants.” High CLIMATE potential would restrict impact. Unlikely to establish as monoculture, but would still significantly displace grass species.

10(b) Impact on medium value EVC? EVC=Damp heathland (D); CMA=Glenelg Hopkins; Bioregion=Glenelg Plain; CLIMATE=M.

10(c) Impact on Low value of EVC? EVC=Wet heathland (LC); CMA=Glenelg Hopkins; Bioregion=Victorian Volcanic Plain; CLIMATE=M. Impact as in 10(a) above.

11. Impact on structure? “Hymenachne can form pure stands that replace native wetland plants” (ARMCANZ 2000)



12. Effect on threatened flora? This species is not documented as posing an additional risk to threatened flora in Victoria.

FAUNA


13. Effect on threatened fauna? This species is not documented as posing an additional risk to threatened fauna in Victoria

14. Effect on non-threatened fauna? “A large infestation of hymenachne is a physical barrier for aquatic and semi-aquatic animals, restricting their territorial movements and breeding activities” (NRM 2001). Can ‘reduce resources available for feeding, breeding and shelter of native fauna’ (Diaz et al 2003). Reduction in habitat for fauna.

15. Benefits fauna? No known benefits to native fauna.

16. Injurious to fauna? Not known to be harmful to fauna. It was grown in Queensland for a high-quality ponded pasture grass (NRM 2001) and in Florida (Hill 1996).

PEST ANIMAL


17. Food source to pests? Not known as a food source to pest animals.

18. Provides harbor? Not known to provide harbor for pest animals.

AGRICULTURE


19. Impact yield? Originally grown in Queensland for a high-quality ponded pasture grass, the species would have no negative impact on yield in grazing situations. It may restrict access to watering points, and its capacity to occur in irrigation channels may impact on the yield of irrigated crops (NRM 2001). However, there is no data to support the level of impact.

20. Impact quality? No data on effect on quality of produce.

21. Affect land values? No data available to determine impact on land value.

22. Change land use? No data available to suggest change in land use.

23. Increase harvest costs? Does not affect harvesting activities.

24. Disease host/vector? None described




Feedback

Do you have additional information about this plant that will improve the quality of the assessment? If so, we would value your contribution.


Assessment ratings originally made by the Victorian Department of Primary Industries.
The entry of this assessment was made possible through the generous support of The Weed's Network.






Attachments:
hymanach via ala.JPG
Capture.JPG
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Date: 19 November 2009; 3:58:26 PM AEDT

Author Name: Niharika Anand
Author ID: anandn