Cistus

Cistus
Cistus monspeliensis
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Malvales
Family:	Cistaceae
Genus:	Cistus L.
Species
See text

Cistus is a genus of flowering plants in the rockrose family Cistaceae, containing about 20 species (Ellul et al. 2002). They are perennial shrubs found on dry or rocky soils throughout the Mediterranean region, from Morocco and Portugal through to the Middle East, and also on the Canary Islands. The leaves are evergreen, opposite, simple, usually slightly rough-surfaced, 2-8 cm long; in a few species (notably C. ladanifer), the leaves are coated with a highly aromatic resin called labdanum. They have showy 5-petaled flowers ranging from white to purple and dark pink, in a few species with a conspicuous dark red spot at the base of each petal., and together with its many hybrids and cultivars is commonly encountered as a garden flower.

The common name rockrose is applied to the species, a name also shared by the related genera Halimium, Helianthemum and Tuberaria, all in the family Cistaceae.

Species

Ecology

They are thermophilous plants, which require open, sunny places. As with many other Cistaceae, the species of Cistus have the ability to form mycorrhizal associations with truffles (Tuber) and are thus able to thrive on poor sandy soils or rocks.

Cistus are the only host of Cytinus hypocistis, a small parasitic plant that lives on the roots and is noticeable only for a short period of time when in flower. The presence of the parasite does not seem to hurt the host population.

Cistus species are used as food plants by the larvae of some Lepidoptera species including Coleophora confluella and Coleophora helianthemella, the latter recorded on Cistus monspeliensis.

Systematics

Cistus and Halimium form a cohesive and the most derived clade within Cistaceae^[1]. Phylogenetic analyses delineated two major lineages within Cistus, a purple-flowered clade and a white-flowered clade, excepting Cistus parviflorus ^[2]. Further analysis of morphological characters show that C. parviflorus has the purple flowers of the purple-flowered clade, but the sessile stigmas of the white-flowered clade, indicating a potential instance of speciation via hybridization.

The white-flowered Cistus lineage was further found to consist of two groups with asymmetric characteristics, which together with ecological evidence, supports the theory of adaptive radiation within this lineage^[3].

Medical Use

Several research groups have a special extract of the rockrose (C. incanus ssp. Tauricus) can show that the propagation of the virus flu viruses (influenza) significantly inhibits in vitro without resistance. Possibly, this research to a new treatment for the flu virus, including bird flu. ^{[4] [5]} The effectiveness in humans, however, with scientific studies have not yet been established.

Cistus salviifolius	Cistus albidus photo taken near Sitges	A flower of × Halimiocistus wintonensis, a garden hybrid of Cistus salviifolius and Halimium lasianthum	Cistus libanotis Photo taken near Cádiz.
Cistus crispus	Cistus purpureus Orchid rockrose	Cistus heterophyllus carthaginensis. Chritically endangered cistus from Cartagena (Spain).

References

External links

• Ellul P., M. Boscaiu, O. Vicente, V. Moreno, J. A. Rossello (2002). Intra- and Interspecific Variation in DNA Content in Cistus (Cistaceae). Annals of Botany 90 (3): 345-351 (available online: full text (html) | full text (pdf)).
• Page, R. G. The Cistus & Halimium Website