The
leaves are borne alternately on the stem. In most species they are 5 to 15 centimetres (2.0 to 5.9 in) long,
pinnate, with (3–) 5–9 (–13) leaflets and basal
stipules; the leaflets usually have a serrated margin, and often a few small prickles on the underside of the stem. Most roses are
deciduous but a few (particularly from South east
Asia) are
evergreen or nearly so.
The
flowers of most species have five petals, with the exception of
Rosa sericea, which usually has only four. Each petal is divided into two distinct lobes and is usually white or pink, though in a few species yellow or red. Beneath the petals are five sepals (or in the case of some
Rosa sericea, four). These may be long enough to be visible when viewed from above and appear as green points alternating with the rounded petals. There are multiple
superior ovaries that develop into
achenes.
[4] Roses are insect-pollinated in nature.
The
aggregate fruit of the rose is a berry-like structure called a
rose hip. Many of the domestic cultivars do not produce hips, as the flowers are so tightly petalled that they do not provide access for pollination. 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, the
hypanthium, which contains 5–160 "seeds" (technically dry single-seeded fruits called
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.
While the sharp objects along a rose stem are commonly called "thorns", they are technically
prickles — outgrowths of the epidermis (the outer layer of tissue of the stem). (True thorns, as produced by e.g.
Citrus or
Pyracantha, are modified stems, which always originate at a node and which have nodes and internodes along the length of the thorn itself.) Rose prickles 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
Rosa pimpinellifolia have densely packed straight prickles, 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 species grow naturally on
coastal sand dunes). Despite the presence of prickles, roses are frequently browsed by
deer. A few species of roses have only vestigial prickles that have no points.
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