Flowers only 2mm across emerge from stems of host plants. The parasite's body is a network of fungus-like threads completely hidden inside the host. Only DNA analysis proves it's actually a flowering plant.
(c) Matt Berger, some rights reserved (CC BY), CC BY 4.0, via Wikimedia Commons
The plant you cannot see
In the arid deserts of Arizona, a plant exists that is almost entirely invisible. Pilostyles thurberi is an obligate endoparasite, meaning it can only survive by living completely inside the tissues of another plant. It has no roots, no leaves, no stem, and no chlorophyll for photosynthesis. Instead, its body consists of a network of microscopic, fungus-like filaments that weave between the cells of its host, drawing all water and nutrients directly from the host's vascular system. This hidden existence means you could examine an infected shrub and have no idea the parasite is there.
The primary hosts for Pilostyles thurberi are desert shrubs in the legume family, most often Emory's indigo bush (Psorothamnus emoryi). The parasite's filaments spread throughout the branches of the host, co-opting its resources. This extreme adaptation makes Pilostyles one of the most reduced forms of a flowering plant known to science. For most of its life, it is a system of threads within another organism.
A tiny, mysterious bloom
The only time Pilostyles thurberi reveals itself is when it flowers. Tiny, reddish-brown buds push through the bark of the host shrub's stems, appearing like small specks or growths. These buds open into flowers measuring no more than 2 millimeters across. The plant is dioecious, meaning each individual produces either male or female flowers, and not both. This necessitates cross-pollination between separate parasitic plants, which may even be growing on different host shrubs.
The flowers typically bloom between January and May. Pollinators are believed to be small insects, such as male Augochloropsis bees and various potter wasps, which are likely attracted by floral scents rather than the tiny visual display. After pollination, the female flower develops into a small fruit containing over 100 minuscule seeds. Each seed measures just 0.2 to 0.3 millimeters.
The plant's classification was a long-standing puzzle for botanists. Its highly simplified body, lacking most typical plant structures, made physical comparison difficult. For years, it was grouped with the family that includes Rafflesia arnoldii, the giant "corpse flower," another parasite with an unusual form. Modern genetic analysis delivered a surprise. DNA sequencing proved that Pilostyles belongs to the order Cucurbitales, making its closest relatives cucumbers, melons, and squash.
💡Fun Facts
*Pilostyles thurberi* is genetically more closely related to a cucumber than it is to the giant parasitic flower *Rafflesia*.
The plant is entirely invisible for most of its life, existing only as a network of threads inside its host.
The name *Pilostyles* comes from the Greek words for "cap" (*pilos*) and "pillar" (*stylos*), describing the shape of the flower's central column.
It is a complete parasite, lacking chlorophyll and unable to perform photosynthesis, deriving all its energy from its host.
Accessible year-round in its natural desert habitat. The tiny flowers are most likely to be visible from January through May.
Admission
Free to find in the wild.
Accessibility
Requires hiking in rugged, open desert scrub environments, typically at elevations between 100 and 1000 meters. Spotting the minute flowers on host shrubs requires a very keen eye and knowledge of the host plant, *Psorothamnus emoryi*.
