subfamily
In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...
of trees, herbs, lianas, and shrubs in the pea family (
Fabaceae
Fabaceae () or Leguminosae,International Code of Nomen ...
) that mostly grow in tropical and subtropical climates. They are typically characterized by having radially symmetric flowers, with petals that are twice divided (valvate) in bud and with numerous showy, prominent stamens.
Recent work on phylogenetic relationships has found that the Mimosoideae form a
clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
nested with subfamily
Caesalpinioideae
Caesalpinioideae is a botanical name at the rank of subfamily, placed in the large family Fabaceae or Leguminosae. Its name is formed from the generic name '' Caesalpinia''. It is known also as the peacock flower subfamily. The Caesalpinioideae a ...
and the most recent classification by ''The Legume Phylogeny Working Group'' refer to them as the Mimosoid clade within subfamily
Caesalpinioideae
Caesalpinioideae is a botanical name at the rank of subfamily, placed in the large family Fabaceae or Leguminosae. Its name is formed from the generic name '' Caesalpinia''. It is known also as the peacock flower subfamily. The Caesalpinioideae a ...
. The group includes about 40 genera and 2,500 species.
Taxonomy
Some classification systems, for example the Cronquist system, treat the Fabaceae in a narrow sense, raising the Mimisoideae to the rank of family as Mimosaceae. The
Angiosperm Phylogeny Group
The Angiosperm Phylogeny Group (APG) is an informal international group of systematic botanists who collaborate to establish a consensus on the taxonomy of flowering plants (angiosperms) that reflects new knowledge about plant relationships disc ...
treats Fabaceae in the broad sense. The Mimosoideae were historically subdivided into four tribes (Acacieae, Ingeae, Mimoseae, and Mimozygantheae). However, modern
molecular phylogenetics
Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
has shown that these groupings were artificial. Several informal subgroups have been proposed, but not yet described formally as tribes. Additionally, the genus ''Acacia'' was recently segregated into five genera (''Acacia sensu stricto'', ''Acaciella'', ''Mariosousa'', ''Senegalia'', and ''Vachellia'').
Basal Mimosoideae
* ''Adenanthera'' group
** ''
Adenanthera
''Adenanthera'' is a genus of flowering plants in the family Fabaceae.
It contains the following species:
* ''Adenanthera bicolor'' Elmer Drew Merrill, Merr. (Sri Lanka)
* ''Adenanthera intermedia'' Elmer Drew Merrill, Merr. (Philippines)
* ''Ad ...
Neltuma
''Neltuma'' is a genus of flowering plants in the pea family (Fabaceae). It includes 43 species native to the Americas, which were previously placed in genus ''Prosopis''. The species range from the southwestern and central United States through ...
Leucaena
''Leucaena'' is a genus of flowering plants in the mimosoid clade of the subfamily Caesalpinioideae of the family Fabaceae. It contains about 24 species of trees and shrubs, which are commonly known as leadtrees. They are native to the Americas ...
Anadenanthera
''Anadenanthera'' is a genus of South American trees in the Legume family, Fabaceae. The genus contains two species, ''Anadenanthera colubrina, A. colubrina'' and ''Anadenanthera peregrina, A. peregrina''. These trees are known to the western wor ...
Paraphyletic
Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
Archidendropsis
''Archidendropsis'' is a genus of flowering plants in the family Fabaceae. It includes 11 species, which are native to Australia, New Guinea, the Bismarck Archipelago, Solomon Islands, and New Caledonia.Blanchetiodendron'' Barneby & J.W.Grimes
** '' Calliandra'' Benth.
** '' Cathormion'' (Benth.) Hassk.
** '' Cedrelinga'' Ducke
** '' Chloroleucon'' (Benth.) Britton & Rose
** '' Cojoba'' Britton & Rose
** '' Enterolobium'' Mart.
** '' Faidherbia'' A.Chev.
** '' Falcataria'' (I.C.Nielsen) Barneby & J.W.Grimes
** '' Hesperalbizia'' Barneby & J.W.Grimes
** '' Inga'' Mill.
** '' Leucochloron'' Barneby & J.W.Grimes
** ''
Lysiloma
''Lysiloma'' is a genus of flowering plants belonging to the family Fabaceae.
The genus is native to the Americas, and species range from Arizona and New Mexico through Mexico and Central America to Costa Rica, and in Florida, Cuba, Hispaniola, ...
Serianthes
''Serianthes'' is a genus of flowering plants in the family Fabaceae. It includes 17 species of trees and shrubs which range from Thailand and Malesia to Papuasia and the South Pacific. New Caledonia has the greatest diversity of species, wit ...
Painteria
''Painteria'' is a genus of flowering plants in the family Fabaceae. It includes two species of shrubs or small trees native to Mexico. Typical habitats include desert grassland and shrubland (matorral) on the Mexican Plateau, and in the lowlands ...
Acacia
''Acacia'', commonly known as wattles or acacias, is a genus of about of shrubs and trees in the subfamily Mimosoideae of the pea family Fabaceae. Initially, it comprised a group of plant species native to Africa, South America, and Austral ...
Parasenegalia
''Parasenegalia'' is a small genus of flowering plants in the legume family, Fabaceae. It belongs to the subfamily Mimosoideae. It is found in tropical areas of the Caribbean, Central America, and South America.
Species list
The genus ''Parasene ...
Vachellia
''Vachellia'' is a genus of flowering plants in the legume family, Fabaceae, commonly known as thorn trees or acacias. It belongs to the subfamily Mimosoideae. Its species were considered members of genus '' Acacia'' until 2009. ''Vachellia'' ...
molecular phylogenetics
Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
polyphyletic
A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...
tribe of legumes in the Mimosoideae that is native to the
tropics
The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...
, subtropics, and warm-temperate regions. It includes five or six genera and some 1,450 species.
* Subdivision – 5 or 6 genera
** ''
Acacia
''Acacia'', commonly known as wattles or acacias, is a genus of about of shrubs and trees in the subfamily Mimosoideae of the pea family Fabaceae. Initially, it comprised a group of plant species native to Africa, South America, and Austral ...
'' Mill. – type genus
** ''
Vachellia
''Vachellia'' is a genus of flowering plants in the legume family, Fabaceae, commonly known as thorn trees or acacias. It belongs to the subfamily Mimosoideae. Its species were considered members of genus '' Acacia'' until 2009. ''Vachellia'' ...
In Bentham's 1842 circumscription of the subfamily Mimosoideae, Acacieae was one of its three constituent tribes, the others being Ingeae Benth. & Hook.f. and Mimoseae Bornn. His Acacieae tribe of 1842 included many genera that were subsequently assigned to tribe Ingeae Benth. In 1875, however, Bentham narrowed his definition of Acacieae so as to include only ''
Acacia
''Acacia'', commonly known as wattles or acacias, is a genus of about of shrubs and trees in the subfamily Mimosoideae of the pea family Fabaceae. Initially, it comprised a group of plant species native to Africa, South America, and Austral ...
'' Mill.
The only morphological character of Acacieae used to distinguish it from the Ingeae is the presence of free stamens (as in tribe Mimoseae). In the Ingeae they are fused in the form of a tube, whereas in the Acacieae only a few species have the stamens fused at the base. Several characters of the foliage, seeds, seed pods, pollen, and stipules are shared by the two tribes. The flower morphology of ''Acacia s.l.'' has characteristics in common with the genera ''
Leucaena
''Leucaena'' is a genus of flowering plants in the mimosoid clade of the subfamily Caesalpinioideae of the family Fabaceae. It contains about 24 species of trees and shrubs, which are commonly known as leadtrees. They are native to the Americas ...
Lysiloma
''Lysiloma'' is a genus of flowering plants belonging to the family Fabaceae.
The genus is native to the Americas, and species range from Arizona and New Mexico through Mexico and Central America to Costa Rica, and in Florida, Cuba, Hispaniola, ...
'' (tribe Ingeae).
The tribal position of monotypic genus '' Faidherbia'' A. Chevalier is equivocal. It was included in the Acacieae by Vassal (1981) and Maslin et al. (2003), but Lewis & Rico Arce placed it in tribe Ingeae following Polhill (1994) and Luckow et al. (2003). In the latter case, tribe Acacieae may conform to genus '' Acacia s.l.'', pending the latter's relationship to other mimosoid genera. ''Faidherbia'' is troublesome as its stamens are shortly united at their base and its pollen is similar to some taxa in the Ingeae.
Description
They are trees, shrubs or lianas, which may be armed or unarmed. Where they have spines, these are modified stipules. In some, prickles arise from the stem's cortex and epidermis. The leaves are bipinnate or are modified to vertically oriented phyllodes. A few have cladodes rather than leaves.
Extrafloral nectaries
Nectar is a viscous, sugar-rich liquid produced by plants in glands called nectaries, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists, ...
may be present on the petiole and rachis, and the pinnule tips may carry protein-lipid Beltian bodies. The leaflets are usually opposite, and are carried on shortly stalks or are sessile. The heartwood is typically red and hard, and the sap of various species hardens into gum.
The inflorescences are dense pedunculate heads or spikes borne in axillary clusters, or are aggregated in terminal panicles. The tetra- or pentamerous flowers are uniformly bisexual, or male and bisexual. Sepals are connate (i.e. fused) and valvate (i.e. not overlapping). The reduced petals are valvate, or rarely absent. The flowers have numerous exserted (i.e. protruding) stamens (>2× as many as the corolla lobes), and their filaments are sometimes connate at their base (forming a short stemonozone). Male flowers of some
Neotropical
The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physically, it includes the tropical terrestrial ecoregions of the Americas and the entire South American temperate zone.
Definition
In biogeogra ...
species have a reduced staminal tube (cf. '' A. albicorticata'', '' A. hindsii'', '' A. farnesiana'', and '' S. picachensis''). Flowers are usually yellow or cream-coloured, but may be white, red, or purple.
The ovary is sessile or stipitate (i.e. supported by a stipe), with many ovules or ovules arranged in two rows. The ovary is attached by a filiform style to a small, capitate stigma. The legume's endocarp is attached to the exocarp, but is otherwise very variable, and may be dehiscent or indehiscent. Seeds are usually elliptic to oblong and flattened to varying degrees. Seeds have a hard black-brown testa (i.e. seed coat) with a pleurogram, visible as a closed or almost closed O-shaped line. Some phyllodinous species have a colourful
aril
An aril (), also called arillus, is a specialized outgrowth from a seed that partly or completely covers the seed. An arillode, or false aril, is sometimes distinguished: whereas an aril grows from the attachment point of the seed to the ova ...
or
elaiosome
Elaiosomes ( ''élaion'' "oil" + ''sóma'' "body") are fleshy structures that are attached to the seeds of many plant species. The elaiosome is rich in lipids and proteins, and may be variously shaped. Many plants have elaiosomes that attract ...