This striking hybrid species has been identified across Massachusetts only recently. With its showy, bright white flowers, the tall shrub becomes conspicuous in May in the area surrounding the interpretive trail in Alper Preserve. One of its parents is believed to be Canada shadbush, the other—smooth shadbush. The hybrid has become independent from both parents and lives its own life as a distinct species. Intermediate shadbush is not uncommon in Plymouth, yet on average it appears to be not nearly as abundant elsewhere as it is in Alper Preserve! Only about a dozen scattered hybrid plants have been identified in Myles Standish SF. First half of May is the best time to observe this plant: the leaves emerge hairy, colored rich russet (which later on fades to just green). While the beautiful dark pink leaves are unfolding, the large white flowers open in upright clusters. If you look inside the flower and observe the ovary, you would find it shiny, devoid of any hairs (glabrous). The large flowers and reddish leaves are inherited from one of the parent species, smooth shadbush. However, in smooth shadbush the inflorescence is drooping and leaves are not hairy even at the earliest stages. This parent species is currently hardly present in our part of the state (there are recent records from Nantucket); alternatively, one has to travel to central or western Massachusetts in order to observe smooth shadbush. Some records of smooth shadbush have been re-identified as intermediate.

April 30, Myles Standish SF, Plymouth

Comparison of flowers: intermediate (left) and Canada shadbush (right). May 12, Myles Standish SF, Plymouth

Comparison of young foliage color: intermediate (in back) and Canada shadbush (at front). May 13, Tidmarsh Farms, Plymouth