One of the most popular flower alternative unity ceremony ideas is the Rose Ceremony. Roses are a traditional symbol of love and are therefore perfect to feature in a wedding ceremony. The ceremony can also feature family members the couple wish to take part.
The couple each has a rose, and so does every family member they wish to take part in the ceremony. (Red roses are usually used due to their colour symbolism of love, and the family members can have the same colour or a different one.) Then the bride and groom swap their roses as a first gift to each other before placing them together into a vase.
Then all of the family members add their roses to the mix.
Of course, you don’t have to use roses for your ceremony—use any flower that has a special meaning to you! Perhaps the flowers you use could be evergreen to symbolise your undying love for one another or sunflowers make a cheery display?