Overview of the generic status of Acacia (Leguminosae: Mimosoideae) Maslin, B. R. Miller, J. T. Seigler, D. S. Australian Systematic Botany 2003 2003-12-31 16 1 18 subg. Acacia subg. Acacia (Grimes 1999 [857,1078,1171,1194] Magnoliopsida Fabaceae Acacia CoL Plantae Fabales 8 9 Magnoliopsida subGenus Acacia   ( Fig. 4)  A cosmopolitan group containing about 161 species ( Table 1) that are distributed as follows:  New World —c.60 species [species numbers derived from information presented in Ebinger et al.(2000)and Clarke et al.(2000)].    Fig. 3. Indicative distribution of tribe  Ingeae.    Fig. 4. Indicative distribution of  Acaciasubg. Acacia(excluding the distribution of A. farnesianain Australia).  Africa(including Madagascar)—73 species [species numbers derived from information presented in Ross (1979), Lock (1989), Boulos (1995), Thulin and Hassan (1996), Thulin (1998), and Du Puy and Villiers (2002)].  Asia(including about 15 species that occur also in Africa)—36 species [species numbers derived from information presented in Ali (1973), Nielsen (1992), Thothathri (1992), Lock and Simpson (1991), Lock and Heald (1994), S. Kumar and P. V. Sane (unpubl. data) and D. S. Seigler (unpubl. data)].  Australia—seven species [species numbers derived from Kodela and Tindale (2001)].  The subgenus may be characterised in the following ways (see Table 4for further details): Trees or shrubs. Branchlets usually lenticellate. Prickles absent. Stipules spinose, in pairs, often being larger and more prominent on young growth, sometimes enlarged and inhabited by ants, rarely absent. Leaves bipinnate, with usually numerous small pinnae (1–15 pairs); leaflets 1–50 or more pairs, from less than 5 to 35 mm long. Petiolar glands mostly small and non-specialised, but large (up to 10 mm in length) and modified in some species. Inflorescence systems simple or racemose; flowers yellow-orange or whitish-yellow, arranged in globose to subglobose heads or cylindrical spikes (8–20 mm in diameter), pentamerous or tetramerous. Floral bracts linear, spatulate to peltate. Ovary sessile, nectariferous tissue not evident. Pods rectangular in cross section or terete, dehiscent or indehiscent, pericarpic strip present or not. Funicle exarillate. Pleurogram large to small. Many studies have shown subg.  Acaciato be monophyletic and clearly distinct from the other two subgenera of  Acacia, for example the cladistic results of Chappill and Maslin (1995)based on morphological data and molecular results of Robinson and Harris (2000), Clarke et al.(2000), Miller and Bayer (2000, 2001, 2003) and Luckow et al.(in press). In one of these studies (Luckow et al., in press),  Acaciasubg. Acaciais shown to be nested deeply within tribe  Mimoseae, a relationship also suggested by Guinet (1990)on the basis of pollen data. There is strong evidence supporting recognition of subg.  Acaciaas a distinct genus (i.e.  Acacia). However, as discussed below, a formal proposal will be made to retypify  Acaciaand, if this is successful, the generic name  Vachelliathen would apply to this group. Currently, there is no universally accepted classification that meaningfully subdivides the species of subg.  Acaciainto subordinate groups. Bentham’s (1875)scheme, which was based on the position of the involucre on the peduncle, is no longer considered suitable for discriminating infra-generic groups ( Ross 1979). Vassal’s (1972)classification, which recognised two subordinate groups (namely subsect. Pluriseriaeand subsect. Uniseriae) on the basis of the arrangement of seeds within the pod, has not been widely adopted. Although Ross (1979)was unable to subdivide the African species meaningfully, a number of those in the Americas were recently accommodated in reasonably distinct, albeit small, informal species groups, namely the A. rigidulagroup ( Lee et al.1989), A. constrictagroup ( Clarke et al.1990), A. farnesianagroup ( Clarke et al.1989; Guinet 1990), A. daemongroup ( Clarke and Seigler 1991) (also called the A. acuiferagroup), the  Acaciamacracanthagroup and the ant acacia group (Janzen 1974; Seigler and Ebinger 1988; D. S. Seigler, unpubl. data). These species    Fig. 5. Indicative distribution of distribution of  Acaciasubg. Aculeiferumsens. str. (excludes sect. Filicinaeand the ‘  Acaciacoulterigroup’). groups were supported by chloroplast data, except for the  Acaciafarnesianagroup ( Miller and Bayer 2003) and the  Acaciamacracanthagroup ( Clarke et al.2000). Miller and Bayer (2003)found a strong separation between New World and African–Asian taxa of subg.  Acacia. The African members of subg.  Acaciathat shared some similarities with  Acaciafarnesianaformed a clade separate from American members of the  Acaciafarnesianagroup. These chloroplast data ( Clarke et al.2000; Miller and Bayer 2003) also support multiple origins of ant associations in the New World and Africa.