The hidden holoparasite
Deep in the damp, shaded soil of deciduous forests, Lathraea squamaria lives a life almost entirely hidden from view. This plant is a holoparasite, meaning it completely lacks chlorophyll and cannot photosynthesize to create its own food. Instead, it derives all of its water and nutrients by attaching to the roots of host trees. Its scientific name reflects its secretive nature: Lathraea comes from the Greek lathraios, meaning "secret" or "hidden," while squamaria is Latin for "with scales," referring to its modified leaves.
For up to a decade, toothwort can exist as a branched, white underground stem system, known as a rhizome, attached to its host. The rhizome is covered in thick, fleshy, scale-like leaves that give the plant its common name, as they resemble a string of teeth. This subterranean network fastens onto the roots of various trees, most commonly hazel (Corylus), alder (Alnus), and elm (Ulmus), but also ash, beech, and walnut. Using specialized structures called haustoria, it penetrates the host's root system to siphon off the resources it needs to survive.
An engineered siphon
The parasitic mechanism of Lathraea squamaria is an example of natural engineering. Its underground scale-leaves are do not photosynthesize but serve a more complex function. Each scale is invaginated, creating a labyrinth of internal cavities. The interior surfaces of these cavities are lined with specialized glandular trichomes, or hairs, that function as hydathodes—glands that secrete water.
These glands actively pump water out of the cavities, a process that requires significant energy. By expelling this water, the plant creates a vacuum, or negative pressure, within the scale's internal chambers. This pressure differential enhances its ability to draw sap from the xylem of its host plant. It is a physical suction mechanism, an active suction mechanism of nutrients. This system allows Lathraea to effectively steal water and dissolved nutrients from the host tree's roots. The process is so active that the secreted water can soften the soil around the plant.
After years spent developing underground, the only part of the toothwort that emerges is its flowering shoot. Between April and May, a creamy-pink to purplish flower spike, growing 8 to 23 cm tall, pushes through the leaf litter. The flowers are two-lipped and drooping in a one-sided spike. They are pollinated primarily by bumblebees (Bombus spp.), which are active early in spring and are attracted to the nectar reward offered when few other plants are in bloom. After flowering and setting seed, the shoot dies back, and the plant vanishes underground once more.