Complex sentence: Topiary at Versailles and its imitators was never complicated: low hedges punctuated by potted trees trimmed as balls on standards, interrupted by obelisks at corners provided the vertical features of flat-patterned parterre gardens.
Split into simpler sentences: Topiary at Versailles and its imitators was never complicated. Typically low hedges were used, punctuated by potted trees trimmed as balls on standards, interrupted by obelisks at corners were the vertical features of parterre gardens.