**2. Biodiversity of Fabaceae in the Amazon region**

In the Amazon, the Italian botanist Adolpho Ducke (1876–1959) pioneered the diversity of the Fabaceae family. In 1925, Ducke published "The legumes of the state of Pará," and, with the progress of his research in the region, in 1949, presented the basic treatise: "The Legumes of the Brazilian Amazon," relating 867 species of Fabaceae [3, 4]. Subsequently, the botany Marlene Freitas da Silva (1937–2005) related the Fabaceae of the Brazilian Amazon with estimates of 1241 species distributed in its three subfamilies: Caesalpinioideae, Mimosoideae and Faboideae [5].

Standing out in the tropical forest in number of species and frequency in the listing of the main timbers exported from the Amazon region, the trees of the Fabaceae family it's adapted in the different ecological environments of this biome. In the world, the geographical distribution of Fabaceae stands out in tropical and subtropical regions and numerically represents the second largest family of Magnoliopsid plants (surpassed by Orchidaceous), estimating global biodiversity in 19,325 species classified in 727 botanical genera [6]. In the different Brazilian biomes, which include the Amazon, Cerrado, Caatinga, Atlantic Forest, Pantanal and Pampas, the diversity of Fabaceae is currently estimated at 2964 species (1458 endemic), 53 subspecies (16 endemic) and 731 varieties (419 endemic), sheltered in 210 genera [7].

#### *Biodiversity of Fabaceae in the Brazilian Amazon and Its Timber Potential for the Future DOI: http://dx.doi.org/10.5772/intechopen.110374*

The Fabaceae of the Amazon are represented in arboreal, shrubby, liana, herbaceous, underwater and aquatic forms. This detachable plasticity of growing habits includes trees of different sizes, occupying the niches of understory to the upper canopy, but also diversified in shrubs, lianas and herbs. In Fabaceae phylogeny, the tree component forms the most primitive group with tropical origin and the most evolved herbaceous group, whose evolutionary differentiation occurred mainly in subtropical zones and even in temperate zones [8].

The family Fabaceae (Leguminosae) is one of the most natural of the Division Magnoliophyte and belongs to the Fabales order. As for phylogeny, Fabaceae are divided into three subfamilies: Caesalpinioideae, Mimosoideae and Faboideae and each has branches consisting of classification tribes. In each subfamily, the distinctions between genera and species are related to floral morphology. Thus, the main differential characteristics between the three subfamilies are [9]:

Caesalpinioideae: These are trees, shrubs and rare herbaceous or scanning plants, distributed mainly in tropical and subtropical regions, with ±180 genera and between 2500 and 3000 species. The leaves are usually pined or sometimes pecked. The flowers are slightly zygomorphic, and the side petals (wings) cover the banner on the button. The stamens are numbered 10 or less (free or monoadelphal). It is considered the most primitive subfamily within the Fabaceae.

Mimosoideae: They are trees, shrubs, woody vines, with few perennial herbaceous, in tropical and subtropical regions, with approximately 56 genera and ± 3000 species. The leaves are usually bipinated, with glands in the raque. The petiole usually presents pulvino and the presence of thorns is common, in those species differentiated in the dry environment, and these may originate from stipulations or occur along the branches. The flowers are regular or actinomorphs, androgynous or unisexual, with valve petals on the bud, with 10 stamens or more. In evolutionary terms, the species of this subfamily are positioned between the Caesalpinioideae and Faboideae.

Faboideae: Trees, shrubs and mainly annual or perennial herbs, distributed in temperate, tropical and subtropical zones, with 400–500 or more genera and > 10,000 species. The leaves are usually pined, but sometimes simple unifolioladas or trifolioladas. The flowers are hermaphrodite, typically zygomorphic, with side petals (wings) covered by the banner, on the button; 10 theses, usually diadelfs (9 + 1), but sometimes monoadelphal or free. The species of this subfamily, especially herbaceous ones, are considered more evolved among the Fabaceae.

The differentiation of species in subfamilies is mainly made by describing their floral morphology (**Figure 2**). Caesalpinioideae species have flowers in ascending pendulums, with five petals and 10 free stamens, e.g. *Aldina heterophylla*, *Campsiandra laurifolia* and *Senna multijuga*. Mimosoideae has flowers consisting of multiple and numerous stamens, defining a particular floral morphology in the set of Fabaceae, e.g. *Hydrochorea marginata*, *Inga cinnamomea* and *Parkia igneiflora*. The Faboideae, the most numerous group, have flowers with five petals and 10 stamens united at the base, or nine united stamens and one free, for example. *Clitoria fairchildiana* and *Dipteryx odorata*.

The most accepted evolutionary theory for the differentiation of Fabaceae attributes the origin of the family in the Mesosolic era, in the Late Cretaceous period, ±97 million years ago [10]. In the Amazon the genus *Hymenaea* (Caesalpinioideae) was researched with an evolutionary and ecological perspective, evidencing the African origin of neotropical species, possibly by migration across the Atlantic occurred at the beginning of the Tertiary (lower Paleocene), when the continents were closer and the tropical rain forest had a larger geographical distribution than the current one [11].

#### **Figure 2.**

*Floral morphology of tree species of Fabaceae from the Amazon region of woody habit and wood interest. Photos: Souza LAG.*

In primitive terms, the subfamily Caesalpinioideae originated the other ones and it is currently considered that the representatives of Faboideae form a more evolved group within the family, with 441 genera and ± 12,300 species with worldwide geographical distribution [8]. Considering phylogeny, the primitive Fabaceae have tropical origin and almost exclusively arboreal growth habit [12]. In fact, 95% of

Caesalpinioideae and Mimosoideae are woody species, frequent and abundant in tropical forests, as well as in the Brazilian Amazon.
