Fabaceae (Leguminosae), the Pea Family
This is a sprawling, multi-branched shrub that grows 10 to 20 feet high. The stems are covered with short, stiff, appressed hairs, as well as scattered, recurved prickles to ½ inch long. The leaves are alternately arranged and bipinnately compound, with 8 to14 pairs of pinnae and 25 to 43 pairs of leaflets. There are solitary, vertical prickles at the intersection of opposing pinnae and paired horizontal prickles on the rachis between each pair of pinnae. Like other members of the genus Mimosa, the leaflets and pairs of pinnae fold together at night and during the day when touched or injured. In Florida, catclaw mimosa blooms throughout the year. The inflorescences are mostly borne in the distal leaf axils. The tiny flowers are densely arranged in globular heads about ½ inch wide. Each flower has four inconspicuous petals and eight prominent stamens, which may be light pink, lilac or white in color. The fruit are flattened pods 1½ to 5 inches long, covered with bristly hairs and borne in clusters of two to 30. At maturity, the pods turn from green to brown and break into buoyant, single-seeded segments. The seeds are flattened, elliptic to oblong in outline, greenish-brown to brown in color and approximately ½ inch long.
Catclaw mimosa is native to Mexico, Central America, South America and probably the West Indies. It is also widely distributed in large parts of continental Africa, as well as the islands of Madagascar and Mauritius, but it is unclear whether it is native or a very early introduction to Africa. This species has escaped from cultivation and naturalized in northern Australia, Southeast Asia, the Galapagos Islands, Hawaii and Florida. While it is most often seen in wet areas (such as stream banks, shorelines and seasonally flooded lands), it can also occur in drier habitats. It tolerates inundation, periodic drought and highly saline conditions, but is intolerant of shade. Currently, catclaw mimosa is restricted to tropical and subtropical regions.
This species has been vouchered by herbarium specimens from a few counties in the southern peninsula. Catclaw mimosa has been found in a variety of habitats in Florida, including scrub, sandhills, coastal berms, shell mounds, mesic flatwoods, strand swamps, depression marshes and ruderal communities.
There are three other species of Mimosa native to Florida (M. pudica, M. quadrivalvis and M. strigillosa), but these are all smaller, low-growing plants with a creeping or prostrate habit. Leadtree (Leucaena leucocephala), another leguminous invasive plant of disturbed wet habitats in Florida, has bipinnate leaves and globose flower heads that may seem superficially similar to catclaw mimosa, but it does not have prickles on its stems or leaves, and its pods are not covered in bristles.
The bristles on the pod segments attach to animal fur, as well as the clothing, shoes and hair of humans. The segments float on water and may also be dispersed in mud that adheres to boats, vehicles and machinery. The seeds have a hard, impermeable coat which allows them to remain dormant for many years, forming large seed banks until they are exposed to conditions optimal for germination. A single, mature plant can produce over 42,000 seeds per year and dormant seeds can remain viable for at least 20 years.
This species was first collected in Florida in 1953 and is thought to have been introduced through intentional cultivation or as a contaminant in imported nursery stock. By 1985, large infestations were noted in South Florida, where it is now estimated to cover 1,000 acres. Catclaw mimosa forms dense, impenetrable thickets that displace native vegetation, choke waterways, and increase sedimentation. In northern Australia, Thailand, Vietnam and Cambodia, catclaw mimosa has become a major weed that is altering wetland ecology and invading pasture and agricultural lands.
This species has been the source of considerable taxonomic confusion, with the same binomial applied to at least three different entities. In his 1991 monograph on New World Mimosa, legume authority Rupert Barneby proposed that the name Mimosa pellita be used for the widespread weedy taxon and Mimosa pigra applied only to an endemic restricted to the Lower Paraná Basin of Argentina and Paraguay. However, Bernard Verdcourt observed that the pantropical weed was already widely known as Mimosa pigra and proposed conservation of this name to the International Botanical Congress, which accepted Verdcourt's proposal. Unfortunately, many online references continue to refer to the invasive species as Mimosa pellita.