Rose
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 hybrid garden rose "Amber
Flush"
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.
Rose thorns are actually prickles –
outgrowths of the epidermis.
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.
