Morphology and mechanical properties of junctions: Implications on the success of clonal spread of cacti

Abstract

Opuntioid cacti reproduce asexually through separation and subsequent rooting of stems (cladodes in platyopuntias; joints in cylindropuntias). Consequently, the force that keeps them together must be overcome. This work assesses the morphometry and disjunction force of joints in Tephrocactus aoracanthus. Morphologically, during their maturation, joints change in shape from oval to spherical, resulting in the youngest being significantly shorter and lighter than the oldest ones. Both critical bending moment and section modulus of junctions resulted in weaker connections on younger joints with respect to older ones, determining that young joints can be separated with less force applied. According to that, their deflection angle is smaller compared to older joints. In relation to other species, the junction of T. aoracanthus is more fragile in both the youngest and oldest joints. This mechanism could favor the spread of T. aoracanthus and its colonization of sites unfavorable for the establishment of its seedlings.