Etymology: "acacia" comes from Greek akis, "spear", because of its thorns. "Mimosa" is its name in the South of France. The name Acacia was spelt with two "c" (" Accacia ") till the end of the XVIIIth century. It is Malherbes, as a defender of the French language, who decided to write Acacia with the only one " c ". Origin: Australia. The Mimosa is cultivated on the French riviera since 1850. Species : 600 species, frequent in dry lands, notably in Africa (look below). Acacia retinodes (Water Wattle, Swamp Wattle, Wirilda, Ever-blooming Wattle or Silver Wattle), flowers the whole year round, hence its popular french name, Mimosa quatre saisons (four seasons). Its leaf (to the right) is simple unlike the leaf of the Acacia which is bipinnate. Habitat: the Mimosa prefers the siliceous soils and grows fast. Hardiness: the Mimosa is slightly hardy (zone 9). It fears big frost (below -7 °C or 19 °F). The severe frost of 1985 burnt the Mimosas of the South of France. They grew again, from the stump.
In case of prolonged cold, the first symptom is the crazing of the bark. They notice then flow of sap which can remind of the "tears" of the grapevine. This flow has tendency to exhaust the tree, but solidify rather fast. Maximum size: 25 m in its origin area; 15 m in France. Bark : smooth, dark grey to reddish-brown. The young stems are covered with a whitish down.
Persistent foliage. Feathery leaves, composed of 12 pairs of leaflets divided into 30 pairs of small leaflets. The colour of leaves varies from light green to glaucous silver. By hot period, leaflets close to limit evaporation. The grown-up tree carries kinds of pruned persistent leaves, in parallel ribs (10-15 cm), which are in reality flattened petioles called " phyllodes ".
Fluffy flowers in pale yellow balls, compiled by 20 and 30, fragrant, blossioming in January (one of the first flowers of the year). The balls are composed of long and very numerous stamens (in common with Silk Tree of the same family). Fruit: smooth and brown pods, with seeds put longitudinally.
If the mimosa seems covered of a kind of milky whiteout, it is an attack of leafhoppers (Metcalfa pruinosa). These insects appeared in 1995 in the South of France and since then, they cause considerable damage in ornamental cultures.
Advices of planting:
Mimosas fearing cold, it is necessary to plant them in a place sheltered from the predominant winds and in a perfectly drained soil. As soon as the temperature reaches -5 °C or 23 °F, envelop the branches in a rainy season veil (count two thicknesses at least).
Acacia with hard wood
Origin: Australia, Tasmania, tropical Africa (its leaves are the food of the giraffes, in spite of the long thorns). Height: 20 m tall. Bark: reddish-brown-grey, grooved. Leaves: true leaves bipinnates and slightly vaulted phyllodes, in parallel ribs, of 6-13 cm. Fruits: pods reddish-brown-red, flat.