Parasitic Plants in Pennsylvania

Among many of the plants that rely on chlorophyll pigments to absorb light during photosynthesis, there are some that will parasitize or partially parasitize nearby plants to reduce their dependence on this process. Sometimes these plants are hidden in plain sight, with green leaves, stems and flowers that look similar to those around it. Other times these plants will look more like a mushroom, being ghost white in appearance with no green resulting from chlorophyll absorption.

There is a wide range of parasitism that occurs within plants. Plants can fully or partially parasitize other plants and even more often fungus within the soil. In today’s post we will be looking at Orobanche uniflora or one-flowered cancer root, a species in the family Orobanchaceae. In Pennsylvania, all members of this family depend on parasitism, with huge differences in plant appearance, location and prevalence.

Light shining through the ghost white pigment of Orobanche uniflora

Orobanche uniflora is entirely parasitic with no green pigment. All of its nutrient intake comes from penetrating roots of suitable host plants with its own root-like structures. These structures are called haustoria and they can absorb water and nutrients directly from the plant roots in which they've penetrated. This full dependency on the host plant classifies Orobanche uniflora as a holoparasite. Again, this means they are not capable of photosynthesis and derive all nutrients from the plants in which they’ve parasitized. Some of the known host plants for O.uniflora include species of Solidago, Helianthus, Sedum and Saxifraga.

A cluster of Orobanche uniflora growing right next to Solidago caesia.

The species name uniflora refers to the single flower bearing stems. There are many different insects that will visit the single blooms of one-flowered cancer root but they are most often cross pollinated by bumble bees and other bee species. Once pollinated, O.uniflora will develop very small seeds that will fall and potentially begin the process of parasitization on viable species. During the spring months keep an eye out in forests for this small but incredibly complex species! In the next post in this series, we will look at a hemiparasite in Orobanchaceae, Agalinis purpurea.

Orobanche uniflora blooming right next to Micranthes virginiensis, a species of Saxifrage