Emergence and flowering in Xanthium spinosum.
Greenhouse experiments and field observations at Orange were conducted with seeds of X. spinosum (collected from 2 sites in New South Wales, at Warren and Leeton) in order to elucidate the reasons for the success of the species in eastern Australia. Seed dormancy varied between sites and was not affected by partial fruit coat removal. Seeds in fruits placed on the soil surface failed to emerge, and burial to depths of 8 cm and deeper significantly reduced emergence compared to burial at 1-4 cm depth. Emergence of seedlings in the field occurred from spring until the end of autumn. In controlled environment studies and in the field, the time to flowering in X. spinosum decreased with decreasing day length. It was concluded that the species' dormancy, wide amplitude of seasonal emergence and ability to flower quickly in cohorts germinating towards the end of the growing season all potentially contribute to its success.