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Mimosa pudica L. 1753
pronounounced: mim-MOH-suh pud-EE-kuh
(Mimosaceae – the wattle family)
common name: Sensitive Plant
Mimosa comes from the Greek μιμος (mimos), an imitator, mimic, because of the movement of the leaves; pudica is from the Latin pudicus, shamefaced, bashful. This is a creeping annual or perennial herb often grown for its curiosity value: the compound leaves fold inward and droop when touched or shaken, re-opening minutes later. The species is native to South America and Central America, but is now a pantropical weed. In Australia it is naturalized in the Northern Territory, Cape York Peninsula, north-east Queensland and as far southwards as south-eastern NSW. The plants photographed are in a lawn: frequent mowing has given them a prostrate habit. Given favourable conditions, these plants can reach a height of a metre or more.
There is a slightly woody branched taproot to 1 m, with thin feeding roots bearing nitrogen-fixing nodules. The stems of the plant are a reddish purple in colour, 30–150 cm long, branching profusely with numerous recurved spines, particularly near the point of attachment of the leaves.
The small dark green leaves are pinnate, consisting of 1 or 2 pairs of opposite segments each with about 12–25 pairs of opposite oblong or linear pointed leaflets 9–12 mm long and 1.5 mm wide with hairy margins. The leaves fold against the branches, not only when touched, but also at night.
The flowers are fluffy heads, purplish to pink, just under 1 cm in diameter, borne on prickly stalks 1.2–2.5 cm long amongst the leaves. On close examination, it can be seen that the floret petals are red in their upper part and the filaments are pink to lavender. The flowers are pollinated by wind and insects.
The fruits are pods 1–2 cm long and 3–6 mm wide, flat, constricted between the seeds, containing up to 5 seeds; they are pointed at the apex and edged with prickles, breaking up into one-seeded segments when ripe to release the seeds, or dehiscing along both margins, but in either event leaving the thickened margin and bristles forming a hairy spider-like structure. The seeds are light brown, flattened, with a slightly granulated surface, 2.5–3 mm long. They have hard seed coats, and this restricts germination.
In contemporary medicine, the plant is being investigated for its potential to yield novel chemotherapeutic compounds. It contains an alkaloid called mimosine, which has been found to have potent antiproliferative (slowing the spread of cancerous cells) and apoptotic (killing cancerous cells) effects.
An interesting piece of trivia: aqueous extracts of the roots of the plant have shown neutralizing effects on the lethality of the venom of the monocled cobra (Naja kaouthia). It appears to inhibit the myotoxicity† and enzyme activity of the cobra venom.
† cause of muscle paralysis
Information about medicinal qualities of plants, or about their use as medicines, is for interest only, and is not intended to be used as a guide for the treatment of medical conditions.
Photographs taken 2011, 2012, Picnic Bay
Page last updated 30th Decmber 2016