Acacia coulteri, , Robinson and Harris, 2000

Maslin, B. R., Miller, J. T. & Seigler, D. S., 2003, Overview of the generic status of Acacia (Leguminosae: Mimosoideae), Australian Systematic Botany 16, pp. 1-18 : 12-13

‘ Acacia coulteri ’ group

( Fig. 7 )

A New World group of 13 species that represent a distinct, but presently undescribed, genus. This group extends from

Arizona south through Mexico to Costa Rica. The ‘ Acacia coulteri ’ group was segregated from Acacia subg. Aculeiferum , partly on account of the lack of prickles and the non-liane habit ( Jawad et al. 2000). Members of this group would presumably have been assigned to sect. Monacanthea. The discrete nature of this group does not appear to have previously been recognised and no generic name for it appears in the literature.

The ‘ Acacia coulteri ’ group may be characterised in the following ways (see Table 4 for further details): Trees or shrubs. Prickles absent. Stipules normally present and scarious, occasionally feebly spinose. Leaves bipinnate, but in one species (A. willardiana) phyllode-like after dehiscence of pinnae; pinnae 2–40 pairs; leaflets mostly less than 7 mm long. Petiolar glands small, solitary, not specialised, sometimes absent in one species. Inflorescence systems simple or racemose, sometimes paniculate; flowers in elongated cylindrical spikes, white, pentamerous. Floral bracts linear. Ovary short stipitate (0.2–0.4 mm), no nectariferous disk at the base of the ovary. Pods chartaceous and dehiscent. Funicle exarillate. Pleurogram relatively large.

While sampling of the ‘ Acacia coulteri ’ group has been small, in recent molecular work there is evidence of early divergence of this group from subg. Aculeiferum sens. str. Miller and Bayer (2003) found members of this group, represented by A. coulteri and A. dolichostachya, outside Acacia subg. Aculeiferum sens. str. and placed in a polytomy with Acacia subg. Phyllodineae , sect. Filicinae, Faidherbia albida and certain Ingeae taxa ( Fig. 1 A ). Clarke et al. (2000) found A. willardiana, another member of the ‘ Acacia coulteri ’ group, on a long branch and sister to subg. Aculeiferum sens. str., again suggesting divergence from other taxa of subg. Aculeiferum . ’

Figures

Fig. 1. (A–F) Schematic diagrams of recent molecular and morphological cladistic studies in pruned form. These are simplified figures based on the strict consensus cladograms of the given study. The original figures have been pruned to represent the relationships among the major lineages. In particular, the figures represent the monophyly, polyphyly or paraphyly of various lineages as indicated in the relevant study. See individual diagrams for references. (A) Chloroplast DNA sequence data. This overview tree was prepared using data from Miller and Bayer (2000, 2001, 2003) and Luckow et al. (2003). (B) Bukhari et al. (1999), cpRFLP, focus on Acacia. (C) Robinson and Harris (2000), cpRFLP, focus on Acacieae. (D) Chappill and Maslin (1995), morphology, focus on Acacieae. (E) Grimes (1999), inflorescence morphology, focus on Ingeae. (F) Clarke et al. (2000), cpRFLP, focus on Acacieae.

Fig. 7. Indicative distribution of distribution of the ‘Acacia coulteri group’.