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 eight genera, 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.
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. 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.
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 the latter don't germinate right 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 together with their small size allows it 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.
Molecular analyses of angiosperms have placed Cistaceae within the Malvales, forming a clade with two families of tropical trees, Dipterocarpaceae and Sarcolaenaceae. Recent phylogenetic studies confirm the monophyly of Cistaceae on the basis of plastid sequences and morphological synapomorphies.
Within Cistaceae, eight genera are recognized, including five in the Mediterranean (Cistus, Fumana, Halimium, Helianthemum, Tuberaria) and three in the temperate regions of North America (Crocanthemum, Hudsonia, Lechea). These eight genera can be grouped into five major lineages within Cistaceae:
- a basal clade of the genus Fumana
- the New World clade of Lechea
- the Helianthemum s. l. clade, consisting of the sister groups Crocanthemum and Hudsonia from the New World, and Helianthemum s. s. from the Old World
- the Tuberaria clade
- a cohesive complex of Halimium and Cistus species
Cultivation and uses
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Cistus, Halimium and Helianthemum are widely cultivated ornamental plants. Their soil requirements are modest, and their hardiness allows them to survive well even the snowy winters of Northern Europe.
Some Cistus species, mostly C. ladanifer, are used to produce an aromatic resin, used in the perfume industry.
The ability of Cistaceae to create mycorrhizal relation with truffle mushroom (Tuber) prompted several studies about using them as host plants for truffle cultivation. The small size of Cistus shrubs could prove favorable, as they take up less space than traditional hosts, such as oak (Quercus) or pine (Pinus), and could thus lead to larger yield per field unit.
Cistaceae has been listed as one of the 38 plants used to prepare Bach flower remedies, a kind of alternative medicine promoted for its effect on health. However according to Cancer Research UK, "there is no scientific evidence to prove that flower remedies can control, cure or prevent any type of disease, including cancer".
These generic names inside Cistaceae were defined in various publications, but their members were synonymised with the eight accepted genera by later research.
Anthelis -- Aphananthemum -- Atlanthemum -- Crocanthemum -- Fumanopsis -- Helianthemon -- Hemiptelea -- Heteromeris -- Horanthes -- Horanthus -- Ladanium -- Ladanum -- Lecheoides -- Lechidium -- Ledonia -- Libanotis -- Planera -- Platonia -- Pomelina -- Psistina -- Psistus -- Rhodax -- Rhodocistus -- Stegitris -- Stephanocarpus -- Strobon -- Taeniostema -- Therocistus -- Trichasterophyllum -- Xolantha -- Xolanthes
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