In this installment of Nature in your Neighborhood, we look at a small white flower and investigate the potential methods of pollination for this species.
Red Elderberry (Sambucus racemosa) is a flowering plant that is native to California and many parts of North America. This plant has multiple variants with the variant most likely seen here as Sambucus racemosa racemosa, also called Sambucus tigranii. The shrub grows up to 6 meters in height with long pointed leaves and produces red berries. As this plant is deciduous, its leaves fall off annually and regrow in the spring. While blooming, racemosa produces small white flowers which initially are red before bloom with recessed petals that are pollinated by bees and hummingbirds. Flowering season is traditionally later in June however flowers have been spotted in late April and early May as shown here.
In bloom it can be confused with another species in the Elderberry family, the Black Elderberry (Sambucus nigra) but can be identified by a few differences seen in their flowers. Black Elderberry also have white flowers however have black berries instead of red ones. The flowers on nigra are organized in a flat dome shape with all flowers coming off one stem, similar to a head of cauliflower. Racemosa has a more pointed flower arrangement with the flowers coming off the main stem similar to branches of a pine tree.
The berries can be used to create jelly or wine while other parts of the plant: stems, bark, leaves and roots contain cyanide as a deterrent to herbivores but not enough to be toxic. Pollen is consumed by certain flies for protein and the berries themselves provide good nutritional value for herbivores. Racemosa has dense roots with rhizomes that anchor it well in soil and prevent soil erosion.
As noted earlier, this plant is pollinated both by pollinators, specifically by hummingbirds and bees. But there is some conflicting information on how pollination is done for this plant. There are some sources pointing towards racemosa being pollinated both by wind and bees. Racemosa’s flowers are small with petals that are recessed which makes the flowers potentially able to be wind pollinated. Looking at the pollen under a microscope shows the pollen having a smooth surface with the shape of a walnut which suggests the pollen is adapted to be spread by wind. However, these flowers also have nectaries that produce nectar and a fragrance that attracts pollinators. This alone should suggest that this favors pollinators over wind-based pollination due to the attraction of pollinators like hummingbirds and butterflies. Later sources seem to conclude that racemosa is pollinated by pollinators.