Using a vegetable peeler or zester, remove the zest of the orange, taking care to leave the pith behind.
In a small saucepan over medium heat whisk together the sugar with 1/4 cup water and the orange zest. Bring to a simmer and remove from heat. Cool to room temperature.
Reserve 4 strawberries for garnish and remove the hulls and roughly chop the remainder. Add the strawberries with the juice of the orange to a blender and fill with ice. Add the cooled orange simple syrup and blend until smooth. Add the rum, if desired, and blend. Pour into glasses and garnish with reserved strawberries.