Organ abscission is a programmed cell separation process that results in the detachment of an entire organ from a plant. Our goal is to understand the signaling pathway that regulates this physiological process. The receptor-like protein kinase, HAESA (HAE), and its paralog, HAESA-like 2 (HSL2), are both expressed in the floral abscission zones in Arabidopsis thaliana. Loss-of-function analyses of either gene do not show any phenotypical change, but the hae hsl2 double mutant shows an abscission-defect phenotype. Examination of the abscission zone by light and scanning electron microscopy showed that the abscission zone in the hae hsl2 appears structurally normal. The force required to remove the petals in wild type and hae hsl2 flowers was measured using a petal breakstrength meter. The force required to remove petals from the hae hsl2flowers at all stages of development was similar to that of wild type flowers that have not yet begun to abscise their petals. Taken together, these data support the role of HAE and HSL2 in the activation of cell separation, rather than differentiation of the abscission zone. Ethylene is also known to promote abscission; therefore we tested the ethylene-induced triple response and the effect of exogenous treatment on floral organ in the hae hsl2, revealing that HAE and HSL2 act independently of ethylene. This implies that the HAE is critical for floral abscission in concert with the action of HSL2.