Rose

A rose is a flowering shrub of the genus Rosa and the flower of this shrub. There are more than a hundred species of wild roses, all from the northern hemisphere and mostly from temperate regions. The species form a group of generally thorny shrubs or climbers, and sometimes trailing plants, reaching 2-5 m tall, rarely reaching as high as 20 m by climbing over other plants.

The leaves of most species are 5-15 cm long, pinnate, with (3-) 5-9 (-13) leaflets and basal stipules; the leaflets usually have a serrated margin, and often a few small thorns on the underside of the stem. The vast majority of roses are deciduous, but a few (particularly in southeast Asia) are evergreen or nearly so.

The flowers have five petals (with the exception of Rosa sericea which often has only four), usually white or pink, in a few species yellow or red. The ovary is inferior, developing below the petals and sepals.

The fruit of the rose is a berry-like structure called a rose hip. The hips of most species are red, but a few (e.g. Rosa pimpinellifolia) have dark purple to black hips. Each hip comprises an outer fleshy layer, and inside containing 5-25 seeds (technically achenes) embedded in a matrix of fine, but stiff, hairs. Rose hips of some species, especially the Dog Rose (Rosa canina) and Rugosa Rose (Rosa rugosa), are very rich in vitamin C, among the richest sources of any plant. The hips are eaten by fruit-eating birds such as thrushes and waxwings, which then disperse the seeds in their droppings. Some birds, particularly finches, also eat the seeds.

Most roses have thorns or prickles. The thorns are typically sickle-shaped hooks, which aid the rose in hanging onto other vegetation when growing over it. Some species such as Rosa rugosa and R. pimpinellifolia instead have densely packed straight spines, probably an adaptation to reduce browsing by animals, but also possibly an adaptation to trap wind-blown sand and so reduce erosion and protect their roots (both of these two species grow naturally on coastal sand dunes). Despite the presence of the thorns, roses are frequently browsed by deer. A few species of roses only have vestigial thorns that have no points.



Roses are subject to several diseases. The most serious is rose rust (Phragmidium mucronatum), a species of Rust fungus, which can defoliate the plant. More common, though less debilitating, are rose black spot, caused by the fungus Diplocarpon rosae, which makes circular black spots on the leaves in summer, and rose mildew, caused by Sphaerotheca pannosa. Roses are also used as food plants by the larvae of some Lepidoptera species.

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