General Information

COMMON NAMES: Sensitive Weed, Shame Plant, Humble Plant, Action Plant, Touch-me-not, Live-and-die; German Sinnpflanze TRADITIONAL NAMES: Rākau Pikika‘a (RR MG), Rākau Avare (AT), Tītā ‘Āvarevare (MK MT), Pikika‘a (AK PL), Lākau Pikikā (PK); Other Polynesian - Vao Fefe (SAM) GLOBAL DISTRIBUTION: NATIVE tropical S.America; EXOTIC EXOTIC circumtropical COOK ISLANDS STATUS: Introduced - Recent, Naturalised; S.Group only - common (RR, AK), uncommon (makatea islands); Land, lowlands - inland valleys SIGNIFICANCE LIST: Medicine; Weed - serious, Injurous spines - moderate KEY FEATURES: Sprawling semi-shrub to 1m. STEMS slender, with curved thorns. LEAVES alternate, compound, a stalk (=rachis) to 5cm with 1-2 pairs of opposite sub-stalks (=pinnae) to 5cm with 10-30 pairs of leaflets. LEAFLETS long-oval to strap-like, to 15x3mm, bluish-green. When touched the leaflets, midribs and stalks fold rapidly at their basal joints. FLOWERS axillary, 1-3 pompom-like clusters, 15mmØ, pink. FRUIT clusters of 10-30 flat pods; edges spiny, to 15x5mm, 2-4 segments; ripen to release 1-seeded segments. SEED flat, round 4mmØ, pale brown.

Cook Islands Distribution

View Distribution Map

Southern Group: Present    Makatea: Present
RR	MG	AT	MK	MT	AK	PL	TK	MN
++++	+	+L	++	+L	++++	+	-	-

Northern Group: -
TN	MH	RK	PK	NS	SW
-	-	-	X?+	-	-

Mimosa pudica Linnaeus
SYNONYMS: Mimosa unijuga; Mimosa pudica var. unijuga

TAXONOMY: PLANTAE; ANTHOPHYTA (=Angiospermae); MAGNOLIOPSIDA (=Dicotyledones); ROSIDAE; Fabales (Legumes); MIMOSACEAE

SIGNIFICANCE NOTES -
POSITIVE SIGNIFICANCE: Medicine
NEGATIVE SIGNIFICANCE: Weed - serious, Injurous spines - moderate. Comments: Recognised on most islands as an injurous and very difficult to control weed in home gardens and in horticultural areas. Produces many seeds and spreads rapidly.

GENERAL NOTE: The how and why of Mimosa leaf-movement At the base of the leaf-stalk (=petiole or rachis) and other leaf-joints there is a swelling, called a pulvinus, with extensor cells that are made rigid by having water pumped into them by cell membrane mechanisms. When the leaflets are jarred or injured the extensor cells become permeable and the water escapes - about 25% within a second - the cells lose turgor and the leaf-stalk droops and the leaflets fold face-to-face. If not disturbed again it takes about 20 minutes for the water pumps to make the extensor cells turgid thereby raising the stalks and spreading out the leaflets. Depending on the level of jarring the touch response, or Nastic Movement, is transmitted to other nearby leaves. The nature of the signal transmitted throughout the leaf and to nearby leaves is unclear with some evidence for three mechanisms: (1) a pressure change in the sap tubes (=xylem cells); (2) a chemical reaction travelling though the sap tubes, and (3) an electrical pulse send through cell membranes. The reason for the rapid response is debated but the main contenders relate to a defence against herbivores by: (1) exposing the stem thorns; (2) appearing less voluminous and appetizing; or (3) scaring by rapid movement. It might also reduce water loss in strong wind. The response also occurs slowly in the evening, or under reduced afternoon light, and the leaflets remain closed throughout the night. This is called a Sleep Movement, and it occurs in many species of plants. Sleep Movement it thought to conserve water to reducing water loss through the stomata of the leaflets. [G.McCormack from many sources, 10/2005]

Vouchers:
Pukapuka: informants reported that it once grew on Motu Ko and had been eradicated (G.McCormack, 2/2004)

References:
p.687 Wagner et al.- Flowering Plants of Hawaii
p.412 Neal - In Gardens of Hawaii
p.734 Hortus 3rd
p.749 Royal Hort. Soc. Index of Garden Plants
p.546 Tropica
p.3/061 A.C.Smith - Flora Vitiensis Nova
p.278 R* Cheeseman - Flora of Rarotonga
p.59 Wilder - Flora of Rarotonga
p.395e Whistler - Ethnobotany of the Cook Islands

Data Update History (information):
zTX, zB02, zM03a, zD02, zupD05b

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