Although the trees themselves may not be dependably male or female, every mulberry flower does have a gender that you can determine for a particular moment in time, even if that gender may change at some point in the future. Tiny mulberry blossoms grow in drooping clusters called catkins . Each of the three species of mulberry has flowers that present slightly differently. The flowers of black mulberry ( Morus nigra ) are small spiky catkins, green in color. Those of the red mulberry ( Morus rubra ) are pale green catkins, while those of white mulberry ( Morus alba ) are small green spikes.