A life of crime
Cytinus ruber is an outlaw of the plant world. As a holoparasite, it has abandoned photosynthesis entirely, producing no chlorophyll, leaves, or true stems. It lives most of its life unseen, as a network of filaments inside the roots of its hosts—shrubs from the rockrose family, primarily pink-flowered Cistus species like Cistus creticus. This internal system, called an endophyte, taps directly into the host's vascular tissue to steal water and nutrients. The plant belongs to the family Cytinaceae, which molecular studies have placed in the order Malvales.
The only time Cytinus ruber reveals itself is to reproduce. From March to May, bright raspberry-red stalks, covered in fleshy scales, erupt from the soil at the base of the host shrub. These stalks are inflorescences, typically no more than 10 centimeters high, each bearing a dense cluster of 3 to 20 flowers. The flowers themselves are small, with white or pale pink perianths peeking out from behind the bright red bracts. A single plant is monoecious, meaning it produces separate male and female flowers on the same inflorescence. The female flowers are located on the upper or outer parts of the cluster, with the male flowers situated below or inside. This arrangement is an important element of its unusual reproductive strategy.
An unlikely alliance
The pollination of Cytinus ruber is an example of a rare biological phenomenon. While bees and other flying insects occasionally visit, its primary pollinators are ants. This is unusual, as ant pollination, or myrmecophily, is not common among flowering plants. Ants can be ineffective pollinators; their bodies are often too small, and many species produce antibiotic secretions from their metapleural glands that can damage pollen.
Cytinus ruber overcomes these challenges with specific adaptations. The plant's low-growing flowers are easily accessible from the ground. Both male and female flowers produce copious amounts of nectar to attract foraging ants. As the ants move through the dense flower cluster to feed, their bodies brush against the anthers of the lower male flowers, picking up pollen. They then transfer this pollen to the large, receptive stigmas of the female flowers located higher up. The female flowers often open a few days before the male ones, which encourages cross-pollination. This entire system is a specialized "pollination syndrome"—a suite of traits evolved in response to a specific type of pollinator. The fact that this occurs in a parasitic plant makes Cytinus ruber a ecological outlier. After pollination, the plant produces a fleshy white berry containing up to 25,000 tiny seeds.