Morphometric, cytogenetic, geographical and ecological evidence for hybridization between Parkinsonia aculeata and Cercidium praecox is presented. Morphometric investigation using the character count procedure and cytogenetic observations confirm hybrid status. All diagnostic morphometric characters were intermediate in the hybrid. Both parents (2n = 28) show regular tetrad formation and pollen fertility greater than 94%. Hybrids have a chromosome number of 2n = 28 or 2n = 30, and display meiotic abnormalities including lagging chromosomes and micronucleus formation; less than 21% of hybrid pollen was fertile. Ecological and geographical information suggests that hybridization is occurring at increasing frequency due to the expanding range of P. aculeata associated with cultivation as an ornamental, coupled with ecological disturbance and weediness, and the cultivation of C. praecox and hybrids as fodder, ornamental and shade trees. Hybrid fertility and phenological observations, in conjunction with F-weighted principal component analysis, suggest that the progeny of F1 hybrids are established. The hybrid is formally described as P. × carterae.
Plant Systematics and Evolution (1999) 216 (1-2) 49-68