Investigation and documentation of hybridization between Parkinsonia aculeata and Cercidium praecox (Leguminosae : Caesalpinioideae)

Morphometric, cytogenetic, geographical and ecological evidence for hybridi zation between Parkinsonia aculeata and Cercidium praecox is presented. Mor phometric 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 tetra d formation and pollen fertility greater than 94%. Hybrids have a chromosom e number of 2n=28 or 2n=30, and display meiotic abnormalities including lag ging chromosomes and micronucleus formation; less than 21% of hybrid pollen was fertile. Ecological and geographical information suggests that hybridi zation is occurring at increasing frequency due to the expanding range of P . aculeata associated with cultivation as an ornamental, coupled with ecolo gical disturbance and weediness, and the cultivation of C. praecox and hybr ids as fodder, ornamental and shade trees. Hybrid fertility and phenologica l observations, in conjunction with F-weighted principal component analysis , suggest that the progeny of F-1 hybrids are established. The hybrid is fo rmally described as P. x carterae.