Cistaceae
The Cistaceae are a small family of plants (rock-rose or rock rose family) known for their beautiful shrubs, which are profusely covered by flowers at the time of blossom. This family consists of about 170(-200) species in nine genera[2] that are not very distinct, distributed primarily in the temperate areas of Europe and the Mediterranean basin, but also found in North America; a limited number of species are found in South America. Most Cistaceae are subshrubs and low shrubs, and some are herbaceous. They prefer dry and sunny habitats. Cistaceae grow well on poor soils, and many of them are cultivated in gardens.
They often have showy yellow, pink or white flowers, which are generally short-lived. The flowers are bisexual, regular, solitary or borne in cymes; they usually have five, sometimes three, petals (Lechea). The petals are free, usually crumpled in the bud, and sometimes in the open flower (e. g. Cistus incanus). It has five sepals, the inner three of which are distinctly wider, and the outer two are narrow and sometimes regarded as bracteoles. The sepal arrangement is a characteristic property of the family.
The stamens are numerous, of variable length, and sit on a disc; filaments are free. The ovary is superior, usually with three carpels; placentation is parietal, with two or more ovules on each placenta. The fruit is a capsule, usually with five or ten valves (three in Helianthemum). The seeds are small, with a hard, water-impermeable coating, weighing around 1 mg.[3][4][5][6][7]
Recently the neotropical tree Pakaraimaea dipterocarpacea is placed here, following APG IV (2016)[8]
The ability of Cistaceae to thrive in many Mediterranean habitats follows from two important ecological properties: mycorrhizal ability and fast renewal after wildfire. Most Cistaceae have the ability to create symbiotic relationship with root fungi of the genus Tuber.[9][10] In this relationship, the fungus complements the root system in its task of absorbing water and minerals from the soil, and thus allows the host plant to dwell on particularly poor soils. In addition, an interesting quality of T. melanosporum is its ability to kill all vegetation except the host plant within the reach of its mycelium, and thus to give its host some sort of "exclusiveness" for the adjacent land area.[10]
Cistaceae have also optimally adapted to the wildfires that frequently eradicate large areas of forest. The plants cast their seeds in the soil during the growth period, but they do not germinate in the next season. Their hard coating is impermeable to the water, and thus the seeds remain dormant for a long period of time. This coating together with their small size allows these plants to establish a large seed bank rather deep in the soil. Once the fire comes and kills the vegetation in the area, the seed coating softens or cracks as a result of the heating, and the surviving seeds germinate shortly after the fire. This mechanism allows the Cistaceae to produce a large number of young shoots simultaneously and at the right time, and thus to obtain an important advantage over other plants in the process of repopulating the area.[3][11]
