Foxglove plants, from the genus Digitalis, are recognized by their tall spikes of tubular, bell-shaped flowers. These biennial or perennial plants are native to temperate regions of Europe but have become naturalized in North America, growing in woodlands, on heathlands, and along roadsides. Plant reproduction relies on pollination, and the ways foxgloves attract animal partners highlight a specialized relationship between the plant and its pollinators.
Key Pollinators of Foxgloves
The primary pollinators of common foxgloves (Digitalis purpurea) are bumblebees, particularly long-tongued species like the common carder bee. The size and strength of bumblebees are suited for the foxglove’s large, tubular flowers, allowing them to push deep inside to access the nectar reward. This is a task smaller insects cannot accomplish. As a bumblebee forages, its hairy body effectively captures and transports pollen. This close fit between flower and pollinator is a result of coevolution.
In some regions, hummingbirds might also act as pollinators, although this is less common for Digitalis purpurea. The bumblebee’s ability to fly in cooler and wetter conditions is also advantageous for foxgloves, which have an extended flowering season.
Floral Adaptations Attracting Pollinators
Foxglove flowers possess features adapted to attract their bumblebee pollinators. The tubular, bell-shaped corolla provides a landing platform and guide for a large insect. The lower lip of the flower is often extended, giving the bee a place to land before it climbs inside. Fine hairs near the entrance can deter smaller insects while also providing extra grip for the intended pollinator.
Visual cues are important in this interaction. Bumblebees are attracted to colors like purple, and the inside of the flower tube is adorned with dark spots or blotches. These markings function as nectar guides, directing the bee toward the nectar produced at the base of the flower.
The Pollination Mechanism in Foxgloves
When a bumblebee enters a flower, its back brushes against the anthers and stigma, which are strategically located on the upper surface of the floral tube. This placement guarantees contact with the dorsal side of the insect’s body. Foxgloves employ a temporal strategy called protandry to encourage cross-pollination. In this system, the male parts of the flower (the anthers) mature before the female part (the stigma).
Flowers on a single stalk mature sequentially from the bottom up. A bee typically starts foraging at the lower, older flowers on one plant before moving upward to the younger, male-phase flowers. This behavior results in the bee collecting pollen from the upper flowers of one plant and then transferring it to the receptive stigmas of the lower, female-phase flowers on the next plant it visits. This mechanism minimizes self-pollination and promotes the exchange of genetic material between different foxglove individuals.
Ecological Significance of Foxglove-Pollinator Interactions
The relationship between foxgloves and their pollinators has considerable ecological importance. For the foxglove, successful pollination by bumblebees leads to the production of thousands of tiny seeds, which are easily dispersed by wind and water, allowing the plant to colonize new areas.
For the pollinators, foxgloves represent a rich and reliable food source. The extended flowering period from late spring to early autumn ensures a consistent supply of nectar and pollen. This is valuable for bumblebee colonies, providing the energy needed for foraging and protein for raising larvae.
This plant-pollinator partnership contributes to the broader health of the ecosystem. By supporting bumblebee populations, foxgloves help ensure the pollination of other native plants and even some agricultural crops that share the same pollinators. The interaction is an example of how the co-evolution of two species can create a stable and mutually beneficial relationship that enhances local biodiversity.