How do parasitic plants survive without making all their own food?

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Botany Theophrastus, statue in the Botanic Garden, Palermo, Italy.

Parasitic plants survive by obtaining nutrients from a host plant through a specialized organ called a haustorium, which penetrates the host and creates a vascular connection between the two plants.1

The extent of their dependence on the host varies:

Hemiparasites: These plants retain some ability to photosynthesize but rely on their hosts primarily for water and mineral nutrients.1
Holoparasites: These are nonphotosynthetic and depend entirely on their hosts for all nutrition. Because they do not produce their own food, they often lack chlorophyll and may have reduced or absent root systems and leaves.1

To ensure survival, these plants have evolved mechanisms to identify and attach to suitable hosts. Some use chemical signals, such as hormones exuded by host roots, to trigger germination, while others use volatile chemicals or visual cues to orient their growth toward a host. While some parasitic plants are considered botanical curiosities, others are weedy species that can cause significant damage to agricultural crops by arresting host growth and reducing yields.1