This is the next in a series on St.Joseph in anticipation of the Solemnity of St. Joseph on March 19.
The flower usually associated with St. Joseph is the white lily. This is because of the tradition that when St. Joseph was among Mary's many suitors, his staff blossomed, confirming that he was God's choice to be Mary's husband. This mirrored the Old Testament account of the flowering of Aaron's staff, which confirmed his priesthood. In iconography, the flowers are usually depicted as white lilies, symbolizing Joseph's purity.
An interesting variation on the theme of St Joseph and the lily, however, involves a blossom that is not actually a lily at all, but an amaryllis:
"Often any stalk of white flowers is called a St. Joseph’s Lily, but there is an actual plant with that name. Hippeastrum johnsonii
is a hybrid amaryllis that, instead of being white, is dark red with
white stripes on the petals. It is called St. Joseph’s Lily because it
often blooms on or near his feast day of March 19,"
Read more here.