Synonyms - Mimosa rubicaulos and Mimosa acanthocarpa were misapplied on early collections.
Family: - Mimosaceae.
Names:
Mimosa is from the Greek mimikos and Latin mimus meaning 'to mimic' and osa meaning 'many' and refers to the many flowers that combine to give the appearance of a single flower.
Pigra is from the Latin pigra meaning 'lazy' or 'slothful' and applied because this plant was not as sensitive to stimulus as other plants in this genus.
Giant Sensitive Tree - because it is large and the leaves fold up when touched.
Other names:
Bashful plant (Hawaii)
Catclaw Mimosa (USA)
Giant Sensitive plant
Giant Mimosa
Mimosa
Thorny Sensitive plant (Thailand)
Summary:
A much branched prickly small tree, with leaves that fold up when touched, a pink globular flower head and seed pods that break into single seeded segments when mature leaving a 'safety pin' like skeleton on the tree.
Description:
Cotyledons:
Two.
First leaves:
Deeply divided once only.
Leaves:
Alternate.
Petiole -
Blade - Bright green, 200-250 mm long, divided to the midrib twice. About 15 pairs of opposite, primary leaflets up to 50 mm long. These consist of many pairs of lance shaped stalkless secondary leaflets. Leaflets fold together when touched, or injured and at night. There is often a pair of prickles on the midrib between the pairs of primary leaflets.
Stems:
Initially green, becoming brown and woody, up to 3000 mm long, much branched. Young stems are rough with short stiff hairs. Random slightly curved thorns, 5-10 mm long.
Flower head:
Globular, 2 in each upper leaf axil, many flowered, 10-20 mm diameter. On stalks, 20-30 mm long.
Flowers:
Pink or mauve. Small.
Sepals -
Petals - 4. Joined.
Stamens - 8. Pink.
Anthers -
Fruit:
Hairy. Flattened pod, 20-25 seeds. In groups in the leaf axil, 65-75mm long, 7-10mm wide. Initially green, turns brown when ripe. Breaks into single seeded segments, leaving a 'safety pin' shaped structure on the bush.
Seeds:
Brown to dark green, oblong, flattened, 4-6 mm long by 2 mm wide.
Roots:
Branching taproot to 2000 mm deep. Crown is woody. Nitrogen fixing nodules on feeder roots. Produces adventitious roots from the stem.
Key Characters:
Biology:
Life cycle:
Perennial. Seed germinates at the start of the wet season or as flood waters recede between November and March. Grows rapidly and branches frequently. The first flowering occurs 4-12 months after germination. Subsequent flowering tends to be between January and March. Stem segments cut or broken from the tree will root and grow.
Physiology:
Reproduction:
By seed.
Flowering times:
January to March usually.
Seed Biology and Germination:
Seed may remain dormant for more than 15 years. When eaten, seed passes through animals unaffected.
Vegetative Propagules:
Hybrids:
Allelopathy:
Population Dynamics and Dispersal:
The hairy pod segments stick to animals and clothing or are transported in mud attached to animals and machines. Flood waters carry many pod segments downstream and is the major method of spread.
It spreads very quickly once introduced to suitable areas and forms impenetrable thickets up to 5000 mm high. One infestation spread from a few plants to over 8000 ha in just 7 years.
A mature plant can produce 90,000 seeds.
Origin and History:
Tropical and sub-tropical areas.
First collected near Darwin in 1891.
Recorded at Adelaide River in the NT in 1952 where it spread downstream and had covered 8000 ha by 1983.
Distribution:
NT.
Habitats:
Climate:
Warm temperate to tropical, humid and sub-humid tropics
Soil:
Wet areas.
Plant Associations:
Significance:
Beneficial:
Used in folk medicine.
Detrimental:
Rapidly spreading weed of roadsides, watercourses, low-lying areas, valleys and seasonally flooded wetlands.
On stream banks it prevents access by stock for water and interferes with recreational and irrigation uses.
On flood plains it makes mustering difficult.
In national parks it eliminates most other species and alters the natural habitats.
Toxicity:
Not recorded as toxic.
Legislation:
Noxious weed of NT, Qld and WA.
Management and Control:
Mowing and slashing are ineffective. Plants cut at ground level have regrown to 2500 mm within 12 weeks. Don't move stock from infested areas to clean areas. Don't transport soil from infested areas. Individual plants should be mechanically removed, with roots, immediately. Early morning applications of dicamba, fluroxypyr and metsulfuron provide control but need repeating to control seedlings. Residual herbicides such as tebuthiuron and karbutilate are useful on some soil types. Other herbicides are useful for cut stump and spot spraying applications. Sprayed areas should be burnt when dead to encourage seed to germinate so seedlings may be controlled.
Thresholds:
Eradication strategies:
Herbicide resistance:
Biological Control:
A biological control program is in progress.
Related plants:
Giant Sensitive plant (M. invisa)
Common Sensitive plant (M. pudica)
Plants of similar appearance:
References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P171. Photo.
Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).
Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #823.2.
Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P443-447. Photos.
Acknowledgments:
Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.