the Oak and the Ivy
oak above is heavily smothered by ivy. The oak's foliage is
golden-brown (usual for this time of year) and the ivy's foliage
is the deep green. The ivy is not feeding on the tree, since it
does not penetrate the bark and manufactures its own food and
obtains nutrients from the soil through its own roots, but it is
simply clinging to the tree, using it for support and it will
drape over walls in similar fashion. The ivy is Britain's only
native evergreen liana or climber, and will also creep across
the floor in the absence of support and can stand on its own,
unsupported, when mature. The stems of the ivy can grow very
thick and woody. I have seen ivy trunks as thick or thicker than
a man's thigh (though typically somewhat flattened) attached to
old oak trees. Eventually, the ivy's foliage may smother the oak
and prevent it from getting enough light and carbon dioxide and
cause it to slowly whither and die. The ivy also adds to the
weight that the tree must support, making it more prone to
damage in high winds. Presumably, the ivy also competes for
water and nutrients from the soil around the tree. However, in a
natural ecosystem, climbers and trees coexist side-by-side, so
the tendency to cut down ivy at first sight is probably not
The ivy clings on by putting out numerous adhesive roots. Climbing plants have touch sensors that direct growth around nearby obstacles. In many climbers these sensors are born on tendrils, as in the passion flower (Pasiflora), and when the tendril touches a solid object it will slowly wrap around the object and
contract, pulling the climber in.
See also sensitive plants to see how climbers find their way by touch!
the common ivy Hedera
is technically a liana (liane) - a woody
climber rooted in
woodland soils, but with its leaves reaching full sunlight. The term vine has a broad sense and a narrower sense. In the narrower sense it is a thin-stemmed herbaceous climbing plant, such as dodder (Cuscuta) - a chlorophyll-lacking parasitic plant. However, ivy is sometimes described as an herbaceous vine, the formation of wood being variable. Rarely it will form a small tree. The grapevine, Vitis, is another example of a liana found in temperate zones.
Scrambling plants like Rubus (bramble) are also abundant in temperate forests. Examples include the various blackberries. These put out arching branches which slowly sway and/or branches which slowly snake across the floor. Both do this to find other plants to lean on for support. Brambles are capable of prolific growth, for example, a branch of Rubus armeniacus will grow several centimetres a day, and be over one cm thick at its base, growing 4-10 metres in one year. This rapid growth is in part possible due to their remarkable construction. Despite being tough and flexible (and protected by large prickles) their central tissues consist largely of light woody pith which reduces weight and can be manufactured more rapidly than dense wood.
The flowers of common ivy are actinomorphic (radially symmetric
about the floral axis) and in groups of about 20 in terminal globose
umbels (rounded umbrella-shapes) or sometimes arranged in
panicles of 1-6 umbels (panicle - an alternately branching
arrangement). There are five very small sepals and 5, sometimes 6,
petals which are yellowish-green and only 3-4 mm and not fused
together. The flowers are hermaphrodite, bearing 5 stamens and an
inferior 5-chambered ovary (inferior - positioned beneath the
stamens on the receptacle). The five styles unite to form a column.
The nectaries form a domed disk surrounding the styles.
Above: shade leaves of Hedera helix
Article updated:9th Jan 2021