The Prosopis Website
prepared by Dieter Geesing
The genus Prosopis possibly originated in tropical Africa where only Prosopis africana, the least specialized species, persists. At the end of the Mesozoic times when the land connections between the continents were easier, the ancestors of today’s species may have migrated widely from the African centre to both east and west and developed into two sharply differentiated parallel groups: a small group of prickly Afro-Asian species with P. africana whose native range stretches from Senegal in the west to Sudan and Kenya in the east, and with P. farcta, P. cineraria and P. koelziana that are native to North Africa and the Middle East; and a big group of American species. The spiny American group of Prosopis species was probably again divided later and became widely separated into two centres, the Mexican-Texan centre and the Argentine-Paraguayan-Chilean one, with the centre of polymorphism in Argentina (where 27 out of 44 known species of the genus Prosopis are found).
Today, the distribution of species from the genus Prosopis ranges from sea level to altitudes of 3700 meters a.s.l., with a variation in annual rainfall from 100 to 1400 mm, but most species are to be found in most semi-arid and arid regions all over the world.
The genus Prosopis consists of 44 recognised species with some common but highly variable generic features. The plants of this genus include tree and shrubs of varying size, predominantly xerophilous (= adapted for growing or living in dry surroundings). Many species often have with multiple trunks.
Leaves are bipinnate (= having both the leaflets and the stems bearing them arranged opposite each other in pairs) with numerous and usually small folioles. Prosopis is a rather primitive genus within the Mimosoidae, as the simple pollen grains, the mostly free petals, and the decandrous (having ten stamens) condition prove (Acacia species are easily distinguished from Prosopis ssp. by having more than 10 stamens per flower). The small hermaphrodite flowers are usually in elongated spikes, first greenish and then creamy-yellow. The flowers are pollinated mainly by bees. Fruits are yellow to brownish coracious bean-like pods, straight, linear, falcate or annular with a coracious mesocarp and are produced in huge quantities in good years. The root system of some Prosopis species belongs to the deepest documented; a live root of an American Prosopis tree was discovered in a copper mine over 50 m below the surface. With a good soil water supply, however, 90% of Prosopis roots are in the upper 100 cm of soil. The deep roots presumably enable a Prosopis tree to survive severe droughts. Prosopis ssp. can be long-lived, probably a couple of centuries in favorable sites.
Pictures: Prosopis pallida pods (left) and Prosopis juliflora flower (right)