7
O.W. Van Auken and J.K. Bush, Invasion of Woody Legumes, SpringerBriefs in Ecology 4,
DOI 10.1007/978-1-4614-7199-8_2, © Springer Science+Business Media New York 2013
Diffi culties with the systematics or taxonomy of the genus Acacia s. l. are not new.
Problems with the systematics of the swollen-thorn acacias were reported 39 years
ago (Janzen 1974 ). This diffi culty has continued up to the present day. Acacia s. l.
was a very large genus 25–50 years ago with 600–1,000 species estimated to occur
worldwide (Turner 1959 ; Janzen 1974 ; New 1984 ). More recently, about 1,350 species have been reported (CPBD 2004 ; Dharani 2006 ), including 954 from Australia,
230 in the Americas, 132 in Africa, 18 in Asia, and possibly ten from some of the
Pacifi c Islands. There is probably some overlap of species occurrence, counts, and
descriptions because of population and clinal variation (Janzen 1974 ; New 1984 ).
However, a number of studies have examined the relationships between the many
species of Acacia s. l. and suggested taxonomic modifi cations of the genus because
it is polyphyletic (see New 1984 ; Seigler et al . 2006 ). Both morphologic, genetic,
and molecular evidence suggested that the former genus Acacia s. l. was polyphyletic and should be separated into as many as fi ve genera including Acaciella ,
Mariosousa , Senegalia, and Vachellia , with the retention of Acacia (Seigler and
Ebinger 2005 ; Maslin 2006 ; Seigler et al . 2007 ; Crow and Ritter 2012 ). The genera
Senegalia and Vachellia include many shrubs and small trees that are common in
arid and semiarid parts of the American southwest. These genera include species
that we are familiar with and species that we have worked with which, for the most
part, we will include and focus on here.
In the new genera Senegalia and Vachellia, there appear to be 146 taxa in the
Americas with a total of 365 taxa worldwide (Seigler and Ebinger 2005 ; Seigler
et al . 2006 ). There seem to be about 86 species and two varieties of Senegalia in the
Americas, 69 taxa in Africa, 43 in Asia, and 2 in Australia with 8 species overlapping in areas. This would be a total of 202 taxa worldwide (Seigler et al . 2006 ). For
Vachellia, there appear to be 60 taxa in the New World, 73 in Africa, 36 in Asia, and
9 in Australia with 15 overlapping for a total of 163 taxa worldwide (Seigler and
Ebinger 2005 ).
Chapter 2
Species Systematics
O.W. Van Auken and J.K. Bush, Invasion of Woody Legumes, SpringerBriefs in Ecology 4,
DOI 10.1007/978-1-4614-7199-8_2, © Springer Science+Business Media New York 2013
Diffi culties with the systematics or taxonomy of the genus Acacia s. l. are not new.
Problems with the systematics of the swollen-thorn acacias were reported 39 years
ago (Janzen 1974 ). This diffi culty has continued up to the present day. Acacia s. l.
was a very large genus 25–50 years ago with 600–1,000 species estimated to occur
worldwide (Turner 1959 ; Janzen 1974 ; New 1984 ). More recently, about 1,350 species have been reported (CPBD 2004 ; Dharani 2006 ), including 954 from Australia,
230 in the Americas, 132 in Africa, 18 in Asia, and possibly ten from some of the
Pacifi c Islands. There is probably some overlap of species occurrence, counts, and
descriptions because of population and clinal variation (Janzen 1974 ; New 1984 ).
However, a number of studies have examined the relationships between the many
species of Acacia s. l. and suggested taxonomic modifi cations of the genus because
it is polyphyletic (see New 1984 ; Seigler et al . 2006 ). Both morphologic, genetic,
and molecular evidence suggested that the former genus Acacia s. l. was polyphyletic and should be separated into as many as fi ve genera including Acaciella ,
Mariosousa , Senegalia, and Vachellia , with the retention of Acacia (Seigler and
Ebinger 2005 ; Maslin 2006 ; Seigler et al . 2007 ; Crow and Ritter 2012 ). The genera
Senegalia and Vachellia include many shrubs and small trees that are common in
arid and semiarid parts of the American southwest. These genera include species
that we are familiar with and species that we have worked with which, for the most
part, we will include and focus on here.
In the new genera Senegalia and Vachellia, there appear to be 146 taxa in the
Americas with a total of 365 taxa worldwide (Seigler and Ebinger 2005 ; Seigler
et al . 2006 ). There seem to be about 86 species and two varieties of Senegalia in the
Americas, 69 taxa in Africa, 43 in Asia, and 2 in Australia with 8 species overlapping in areas. This would be a total of 202 taxa worldwide (Seigler et al . 2006 ). For
Vachellia, there appear to be 60 taxa in the New World, 73 in Africa, 36 in Asia, and
9 in Australia with 15 overlapping for a total of 163 taxa worldwide (Seigler and
Ebinger 2005 ).
Chapter 2
Species Systematics