Invasiveness Assessment - Hymenachne, olive hymenachne (Hymenachne amplexicaulis) in Victoria (Nox)
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Plant invasiveness is determined by evaluating a plant’s biological and ecological characteristics against criteria that encompass establishment requirements, growth rate and competitive ability, methods of reproduction, and dispersal mechanisms.
| Each characteristic, or criterion, is assessed against a list of intensity ratings. Depending upon information found, a rating of Low, Medium Low, Medium High or High is assigned to that criterion. Where no data is available to answer a criterion, a rating of medium (M) is applied. A description of the invasiveness criteria and intensity ratings used in this process can be viewed here. |
The following table provides information on the invasiveness of Hymenachne, olive hymenachne.
A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:
Victorian Weed Risk Assessment (WRA) method (PDF - 630 KB)
Victorian Weed Risk Assessment (WRA) method (DOC - 1 MB)
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Common Name: Hymenachne, olive hymenachne
Scientific name: Hymenachne amplexicaulis
| Question | Comments | Rating | Confidence |
| Establishment | |||
| 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). | H | MH |
| Establishment requirements? | Sets viable seed after flowering – the seeds germinate on damp bare ground Seeds set from late autumn to early spring (KEC 1991). | ML | M |
| How much disturbance is required? | Occurs in shallow waters of swamp margins and river banks (Weber 2003). | MH | MH |
| Growth/Competitive | |||
| Life form? | A robust perennial grass / semi-aquatic (Wildin 1989). | H | H |
| Allelopathic properties? | None described in consulted references. | L | MH |
| 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). | M | H |
| 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). | H | MH |
| Stress tolerance to frost, drought, w/logg, sal. etc? | Tolerant of drought and flood (Wildin 1988). | MH | H |
| Reproduction | |||
| Reproductive system | Rhizomatous and sets seed (Hill 1996). | H | MH |
| 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). | H | MH |
| 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. | M | L |
| Reproductive period? | Species forms self-sustaining dense monocultures (Hill 1996). | H | MH |
| Time to reproductive maturity? | Perennial grass (Wildin 1989) – therefore assume maturity within first year | H | H |
| Dispersal | |||
| 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). | H | MH |
| 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. | H | M |
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