(Photograph = Tristerix aphyllus on Echinopsis chiloensis, Patricio-Novoa-Quezada)
Introduction
Tristerix aphyllus is a holoparasitic mistletoe that lives almost entirely inside its cactus hosts. You don’t see leaves or stems—only clusters of orange tubular flowers (and later pale fruits) that burst through the cactus skin. This mistletoe has no chlorophyll and relies on its host for water and food.
The Details
What it parasitizes
In central Chile, T. aphyllus most often infects the tall, columnar cactus Echinopsis chiloensis; it can also occur on Eulychnia acida. Larger, older cacti are infected more frequently than small ones.
How it gets inside
Birds eat the sticky fruits and deposit seeds on cactus surfaces and spines. A germinating seed sends a haustorium through the outer tissues, and the parasite spreads internally as a network of strands. Months or years later, flowering shoots push outward—usually through softer spots like areoles—so the flowers and fruits sit at the surface while the rest of the plant remains hidden within.
Pollinators and dispersers
Day-active birds visit the bright flowers for nectar and transfer pollen between infections. Mockingbirds and other fruit-eating birds then spread the seeds, completing the cycle.
Effects on the host
Infected cacti often show reduced flower and fruit production compared to similar, uninfected plants. Heavy infestations can divert resources away from growth and reproduction. Because the parasite remains inside, infections can go unnoticed until the floral clusters appear.
About the host cactus
Echinopsis chiloensis (formerly Trichocereus chiloensis) is a handsome columnar species that can exceed 20 feet. It occurs from around Talca north to the Elqui Valley, with local forms across its range. Some plants begin flowering at roughly three feet tall, which makes it possible to compare reproduction in infected and uninfected individuals in the field.
Additional Reading: Studies of Tristerix aphyllus Infecting Trichocereus chilensis
