Mexican ricegrass (Achnatherum clandestinum)

Present distribution

Scientific name:	Achnatherum clandestinum (Hack.) Barkworth
Common name(s):	Mexican ricegrass

This weed is not known to be naturalised in Victoria

Habitat:

Native to Mexico. Abundant in disturbed (roadsides and fencerows) and overgrazed areas (Barkworth et al 1989). Species not known as naturalised in Victoria (DSE 2004, ANH 2006).

Potential distribution

Potential distribution produced from CLIMATE modelling refined by applying suitable landuse and vegetation type overlays with CMA boundaries

Map Overlays Used

Land Use:
Pasture dryland; pasture irrigated

Broad vegetation types
Grassland; plains grassy woodland

Colours indicate possibility of Achnatherum clandestinum infesting these areas.

In the non-coloured areas the plant is unlikely to establish as the climate, soil or landuse is not presently suitable.

map showing the potential distribution of Mexican rice grass

Red= Very high	Orange = Medium
Yellow = High	Green = Likely

Impact

QUESTION	COMMENTS	RATING	CONFIDENCE
Social
1. Restrict human access?	Erect culms 50-80 cm long (Clayton et al 2006). In Mexico it is abundant in disturbed (roadsides and fence rows) and overgrazed areas (Barkworth et al 1989). Unlikely to restrict human access.	l	h
2. Reduce tourism?	In Mexico it is abundant in disturbed (roadsides and fence rows) and overgrazed areas (Barkworth et al 1989). Weed not likely to impact upon tourism.	l	h
3. Injurious to people?	Sharp-pointed leaves (Barkworth et al 1989). May cause some minor physiological issues.	ml	h
4. Damage to cultural sites?	Weed not documented to cause damage to cultural sites. Little or negligible effect on aesthetics or structure.	l	h
Abiotic
5. Impact flow?	Terrestrial species (Barkworth et al 1989).	l	h
6. Impact water quality?	Terrestrial species (Barkworth et al 1989).	l	h
7. Increase soil erosion?	Plants increase soil compaction (Barkworth et al 1989). Low probability of large scale soil movement.	l	h
8. Reduce biomass?	In Mexico it is abundant in disturbed (roadsides and fence rows) and overgrazed areas (Barkworth et al 1989). Erect culms 50-80 cm long (Clayton et al 2006). In these instances where it is growing in disturbed areas, likely that it may increase biomass.	l	h
9. Change fire regime?	Grows in disturbed (roadsides and fencerows) and overgrazed areas (Barkworth et al 1989) up to 80cm high (Clayton et al 2006). May contribute to a minor change in frequency and / or intensity of fire risk.	ml	mh
Community Habitat
10. Impact on composition (a) high value EVC	Potential distribution of Achnatherum clandestinum excludes Victoria. No impact on EVCs in Victoria.	l	mh
(b) medium value EVC	Potential distribution of Achnatherum clandestinum excludes Victoria. No impact on EVCs in Victoria.	l	mh
(c) low value EVC	Potential distribution of Achnatherum clandestinum excludes Victoria. No impact on EVCs in Victoria.	l	mh
11. Impact on structure?	‘.. increases plant destruction in the areas between the tussocks, thereby lowering the carrying capacity of the pasture or range’.. ‘can become a significant problem in grazed and disturbed areas’ (Barkworth et al 1989). Suggests that the plant may have a minor effect on the lower strata.	ml	h
12. Effect on threatened flora?	This species is not documented as posing an additional risk to threatened flora.	mh	l
Fauna
13. Effect on threatened fauna?	This species is not documented as posing an additional risk to threatened fauna.	mh	l
14. Effect on non-threatened fauna?	‘.. increases plant destruction in the areas between the tussocks, thereby lowering the carrying capacity of the pasture or range’.. ‘can become a significant problem in grazed and disturbed areas’. Browsed by goats and horses but avoided by cattle (Barkworth et al 1989). May lead to a minor reduction in food for non-threatened fauna species.	ml	h
15. Benefits fauna?	Browsed by goats and horses but avoided by cattle (Barkworth et al 1989). Would provide very little support to desirable species.	h	h
16. Injurious to fauna?	‘The sharp-pointed leaves make S. clandestina a potential problem … making the tips difficult for browsing cattle to avoid’ .. ‘Cattle avoid trampling on tussocks’ (Barkworth et al 1989). The leaves may have a minor impact on fauna.	ml	h
Pest Animal
17. Food source to pests?	Browsed by goats and horses but avoided by cattle (Barkworth et al 1989). Weed would provide minimal food for pest animals in Victoria.	l	h
18. Provides harbour?	Weed not known to provide harbour for pest species.	l	h
Agriculture
19. Impact yield?	‘.. increases plant destruction in the areas between the tussocks, thereby lowering the carrying capacity of the pasture or range’ (Barkworth et al 1989). Weed would have a minor impact on the quantity of produce.	ml	h
20. Impact quality?	Weed not documented to impact upon the quality of produce.	l	mh
21. Affect land value?	Weed not documented to affect value of land.	l	mh
22. Change land use?	Weed not documented to cause a change in priority of land use.	l	mh
23. Increase harvest costs?	Weed not documented to increase harvest costs.	l	mh
24. Disease host/vector?	Weed not documented as a host or vector for disease of agriculture.	l	mh

Invasive

QUESTION	COMMENTS	RATING	CONFIDENCE
Establishment
1. Germination requirements?	Insufficient information to determine germination requirements.	m	l
2. Establishment requirements?	In Mexico it is abundant in disturbed (roadsides and fence rows) and overgrazed areas (Barkworth et al 1989). This would suggest that the plant prefers open spaces but insufficient information to determine whether the plant can establish under a moderate canopy.	m	l
3. How much disturbance is required?	In Mexico it is abundant in disturbed (roadsides and fence rows) and overgrazed areas (Barkworth et al 1989). Establishes in highly disturbed natural ecosystems.	ml	h
Growth/Competitive
4. Life form?	Stipoid grass (Barkworth et al 1989). Life form – grass.	mh	h
5. Allelopathic properties?	None described however not a lot of literature available on this species.	m	l
6. Tolerates herb pressure?	Avoided by cattle but grazed by goats and horses. ‘In general, however, S. clandestina is an undesirable grass on rangelands’ (Barkworth et al 1989). Consumed but non-preferred.	mh	h
7. Normal growth rate?	Insufficient information to determine rate of growth.	m	l
8. Stress tolerance to frost, drought, w/logg, sal. etc?	Suggested that the grass may have been taken to Texas when searching for a drought-resistant species (Barkworth et al 1989). However, insufficient information to determine tolerance to other stresses.	m	l
Reproduction
9. Reproductive system	‘The long anthers suggest S. clandestina is cross-pollinated, but it almost must be self compatible because additional florets occur in the basal leaf sheaths’ (Barkworth et al 1989). Reproduces sexually – through both self and cross-pollination.	ml	h
10. Number of propagules produced?	‘Each culm produces an abundance of florets, almost all of which produce viable seed’ (Barkworth et al 1989). Insufficient information to determine number of propagules produced per flowering episode.	m	l
11. Propagule longevity?	Insufficient information to determine propagule longevity.	m	l
12. Reproductive period?	Insufficient information to determine reproductive period.	m	l
13. Time to reproductive maturity?	Insufficient information to determine time to reproductive maturity.	m	l
Dispersal
14. Number of mechanisms?	‘ seeds will attach themselves to animal coats, although not very securely’ (Barkworth et al 1989). Propagules spread by animals.	mh	h
15. How far do they disperse?	‘.. seeds will attach themselves to animal coats, although not very securely’ (Barkworth et al 1989). Likely that many propagules will reach between 200-1000m.	mh	h

References

Barkworth, M.E., Valdes-Reyna, J. & Landers, Jr, R.Q. 1989, ‘Stipa clandestine: new weed threat on southwestern rangelands’, Weed Technology, vol. 3, pp. 699-702.

Clayton, W.D., Harman, K.T. & Williamson, H. (2002 onwards). World grass species: descriptions, identification, and information, viewed 29 Aug 2006, http://www.kew.org/data/grasses–db.html

Global present distribution data references

Barkworth, M.E., Valdes-Reyna, J. & Landers, Jr, R.Q. 1989, ‘Stipa clandestine: new weed threat on southwestern rangelands’, Weed Technology, vol. 3, pp. 699-702.

Global Biodiversity Information Facility (GBIF) 2006, Global biodiversity information facility: Prototype data portal, viewed 01 Aug 2006, http://www.gbif.org/

Missouri Botanical Gardens (MBG) 2006, w³TROPICOS, Missouri Botanical Gardens Database, viewed 01 Sep 2006, http://mobot.mobot.org/W3T/Search/vast.html

United States Department of Agriculture (USDA) 2006, PLANTS Profile, Natural Resources Conservation Service, Plants Database, viewed 30 Aug 2006, http://plants.usda.gov/

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