The Argentine flora is not yet fully known. Up to now there is no overall work that gives a somewhat complete aspect of the phytogeographic physiognomy of the country; only Patagonia has been the subject of numerous and accurate works carried out by eminent botanists such as Spegazzini and Haumann, among those who have resided in the country, and as Hooker, Skottsberg, Dusen and others among the foreigners who explored and studied materials collected in the wide plateau Patagonian. On other regions of the country there are not even summarized catalogs and there are provinces and large extensions of indisputable economic interest on which there is not a single botanical work.
Grisebach in 1872 in his work on the vegetation of the world, sketched the botanical physiognomy of the Argentine republic. A few years later Dr. PG Lorenz published his Cuadro de la vegetación argentina, adopting the divisions of Grisebach. In 1881 Dr. EL Holmberg, collaborating in the census of the province of Buenos Aires, wrote an essay on the flora of that province which he repeated in the chapter on the Argentine flora, which appeared in the book of the general census of the Argentine republic (1895).
According to insidewatch.net, Dr. Carlo Spegazzini also published at the beginning of this century, a phytogeographic system of Argentina, which was followed with slight modifications by Haumann in his botany (1910).
The most recent study (1920) on the appearance of the country’s vegetation is due to the latter botanist, who for 20 years worked carefully on the Argentine flora. Haumann distinguishes the following regions and formations: 1) the Patagonian steppe; 2) the sub-Antarctic woods; 3) the forest and the corresponding Andean area; 4) forests and sub-tropical covered areas; 5) the Pampean prairie; 6) Mesopotamia.
It is not possible to establish with precision the exact limits of all these formations, because, as we have said, the studies as a whole are varied, and there are in nature transition zones through which one passes insensibly from one formation to the other.
Until a few years ago, the most important work from the floristic point of view for Argentina were the Symbolae ad Floram Argentinam of Grisebach, published in Gottingen in 1878 and which cite 2265 species of vascular plants in the center, NE., And E. (Entre Ríos) of the town, collected by doctors PG Lorenz and J. Hieronymus. According to an approximate calculation, the vascular species that live spontaneously in the vast Argentine territory are 10,000. The National Museum of Natural History in Buenos Aires has started the edition of a catalog raisonné of the Argentine flora, of which two volumes have so far been published, one for the Gymnosperms and Monocotyledons, and another for a part of the Dicotyledons (Salicaceae- Droseraceae).
The average annual rainfall reaches between 100 and 500 millimeters and the number of rainfall varies from 20 to 50 according to the year.
Typical plants are xerophilous trees or shrubs, often without leaves or with very small leaves, in some cases coated with resin, in others with thorns.
The main elements of the forest are the jurillas, Zigofillacee, the genus Larrea corresponding to three different species: L. divaricata Cav., L. nitida Cav. and L. cuneata Cav., constant shrubs in this formation, especially the first species; the second characterizes the southern part of the formation better together with the red salicc that flanks the edges of the Chubut river (Salix Humboldtiana Willd.). There is another Larrea in Argentina which is however in the Patagonian formation; is a tortuous shrub lying on the ground, described by Spegazzini with the name of Larrea Ameghinoi, in honor of the famous paleontologists of this surname. The leaves of jarillas are coated with abundant resin, wax, fat, rubber; they are used in popular medicine, as diaphoretics, febrifuge, and emmenagogues, the green branches are used to dye the wool, to which they communicate the same color.
Other elements are: the chañar (Gourliea decorticans Gill.) Leguminosae with beautiful yellow flowers; the brea (Cerdium praecox [R. et Pav.] Harms.), also leguminous, clearly distinguished from the other trees of the forest by its trunk and by the fairly bright green branches, which secrete a rubber of industrial application; the molle, polymorphic anacardiacea of the genus Schinus (Sch. dependens O rt.), which is distinguished by the galls it generally carries, originating from various insects; the piquillín, ramnacea of the genus Condalia ; l ‘ atamisque or mata negra, monotypic capparidacea of the genus or sombra del toro, hemiparasitic santalacea of the tala, densely covered by rhomboid leaves, hence the specific name of Iodina rhombifolia, etc.
Among the spots we can observe the peleus, a medicinal shrub of the Verbenaceae family (Lippia turbinata Gris.) And other species of this family and of the Solanaceae family (genera Lycium and Grabowskia). But, above all, we must remember the Leguminosae Mimosoidee of the genera Prosopis and Acacia.
The algarrobo or better algarrobo blanco occupies most of the extensions of this formation; its botanical name is Prosopis alba Gris. It is a beautiful tree that does not reach great height; the delicate foliage produces a very pleasant shade, its flowers are gathered in dense spikes that stand out for the yellow color of the stamens. It is very beneficial in the regions where it lives, and it is therefore that by definition it is called “the tree”, the fruit and the seed are rich in sugary principles, and are a very popular food, both for humans and for animals.: reduced to flour they are used to make pies (patayes), and fermented they produce the alcoholic drink called aloja. Livestock willingly eat legumes that fall from trees, an important resource for pastoralism, especially in times of greatest drought, when the lack of natural forage is almost absolute. The algarrobo negro (Prosopis nigra Gris.) Is very similar to the previous one, although its bearing is less quick; its fruit when ripe is black; it is less frequent than white.