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 of most species roses 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.
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.
