• Mimosa is a megadiverse neotropical genus, with more than 550 species, and ca. 40 species in Old World, but several species became pantropical.
  

See the post showing the distribution of Mimosa using the Leaflet R package (Cheng et al. 2018).

• Mimosa L. belongs to clade Mimosoid, within the family Leguminosae (LPWG 2017).

• The last taxonomic revision of the genus was performed by Barneby (1991).

  Classification of Barneby (1991)

  tela cheia
  Diagnostic characters of sections, according Barneby (1991):

  • Sect. Mimadenia

    • leaf nectaries
    • setiform trichomes
    • diplostemonous flowers
      

  • Sect. Batocaulon

    • leaf nectaries
    • setiform trichomes
    • diplostemonous flowers
      

  • Sect. Calothamnos

    • leaf nectaries
    • setiform trichomes
    • dendritic & stellate trichomes
    • yellowish, isostemonous flowers
      

  • Sect. Habbasia

    • leaf nectaries
    • setiform trichomes
    • diplostemonous flowers
      

  • Sect. Mimosa

    • leaf nectaries
    • setiform trichomes
    • isostemonous flowers
      

• The most comprehensive phylogenetic study of Mimosa proved its monophyletic status (Simon et al. 2011).
  

  Main clades by Simon et al. (2011)

  

  • Sect. Mimadenia is the only monophyletic section in the genus, according Barneby’s (1991) infrageneric classification.

  • A new classification based on phylogenetic studies is expected for the genus.

• Mimosa is characterized by its bipinnate and paripinnate leaves, capitate or spicate inflorescence, 3–6-merous flowers, iso- or diplostemonous, and craspedium fruit, with articulated or non-articulated epicarp, and differs from other similar mimosoids by the 6-12 stamens and absence of glands on the anthers (Barneby 1991; Barroso et al. 1999).

  • Bipinnate and paripinnate leaf Leaf of M. diplotricha

Mimosa is especially distinguished by two peculiar leaf structures:

1. Paraphyllidia

   • Pair of leaf-like projections developed between the pinna-pulvinus and the first pair of leaflets
   • often present
   • form/shape: often linear, lanceolate, short-triangular (or conic), or oval with acute apex Short-triangular (or conic) paraphyllidia of M. bimucronata Lanceolate paraphyllidia of M. monticola, unequal in size

2. Spicule

   • Projection developed at the interpinnal space on abaxial face of leaf-rachis
   • present or absent
   • form/shape: short-triangular (or conic), linear-subulate, or spiniform short-triangular (or conic) spicule of M. arenosa
     Linear-subulate spicule of M. diplotricha
     Spiniform spicule of M. pigra
     

The presence of leaf-nectaries is rare in the genus

• Only present in M. sect. Mimadenia Barneby
  • Composed by only 16 species
  • Sister group of all other Mimosa groups (Simon et al. 2011)
  • The presence of leaf-nectaries is also reported in outgroups (of Piptadenia group). Hence, their presence in Mimosa is a plesiomorphic trait Leaf-nectary of M. extensa
    

Recognize different types of trichomes is very important for species identification

The main types of trichomes are:

1. Filiform

   • Simple (not-branched), uniseriate Abaxial surface leaflet of M. cubatanensis with filiform trichomes denser at the base Rachilla of M. arenosa sparsely covered with filiform trichomes
     

2. Setiform

   • Simple (not-branched, but sometimes with minute projections), multiseriate Abaxial surface leaflet of M. sensitiva showing both filiform (smaller) and setiform (bigger) trichomes Abaxial surface leaflet of M. pigra with setiform trichomes with minute projections Stipule of M. elliptica with setiform trichomes with dilated base

3. Stellate

   • Multiangulate branched, sessile, subsessile, or stalked, peduncle multiseriate Stellate-subsessile or -sessile trichomes of M. schomburgkii Stellate-stalked trichomes of M. schomburgkii
     

4. Dendritic

   • Multiseriate axis, densely branched Dendritic trichomes of M. pilulifera var. pseudincana

5. Glandular

   • Subsessile or stalked Glandular-subsessile trichomes of M. paludosa Glandular-stalked trichomes of M. paludosa

Inflorescence types

• Capitate

• Spicate

Flower morphology is one of the most important diagnostic character

1. Merosity

   • Most species is tetramerous, but others are trimerous, pentamerous, and, rarely, hexamerous

     Tetramerous flower of M. bimucronata

   • Trimery is a rare condition, and evolved independently at least six times in the genus (Simon et al. 2011)

   • Mostly are natural from the Brazilian Caatinga

     Trimerous flower of M. caesalpiniifolia

2. Calyx

   • Campanulate

     Campanulate calyx of M. elliptica

   • Pappiform (term used by Barneby 1991 in allusion to the pappiform calyx of Asteraceae)

     Pappiform calyx of M. pigra

3. Number of stamens

   Character mapping by Simon et al. (2011)

   

   • Diplostemonous

     • Plesiomorphic trait
     • Sect. Mimadenia, Batocaulon (few exceptions) and Habbasia
       

   • Isostemonous

     • Apomorphic trait
     • Sect. Calothamnos and Mimosa
       

4. Color of stamens

   • Whitish

     • Many
       

   • Pinkish

     • Many
       

   • Purplish

     • Many
       

   • Yellowish

     • Sect. Calothamnos (see M. furfuracea)
       

   • Reddish

     • M. myriophylla
       

Fruit type

• Craspedium, a type of legume with a persistent margin (replum) and which its epicarp is, generally, divided into monospermic and caducous articles (articulated) or the entire epicarp is divided into two caducous valves (non-articulated) Craspedium with articulated epicarp of M. campicola Craspedium with non-articulated epicarp of M. ceratonia

Some photos