Tuesday, 10 July 2012

Wednesday wildflower: ivy

The name ivy conjures up evocative images of established gentry in the northern hemisphere: old buildings covered in ivy, the Ivy-League colleges in the US, and the holly and the ivy at Christmas.  In New Zealand, the reality is not so pretty.  Ivy is an aggressive and unwelcome weed, partly because many people still plant it, or at least tolerate it until it's too late.
Ivy, Hedera helix.  A, juvenile leaves; B, adult leaves; C, an umbel at flowering; D, an immature fruit; E, flower stalk to show the stellate hairs; F, flower, side view; G, young shoot to show the adventitious roots that the plant uses for attachment; H, flower from above.
The familiar lobed ivy leaf is the juvenile form (A above).  When the plant climbs into the sunlight and flowers, its leaves are generally simple (B above).
Ivy flowers and mature leaves, Kelburn, Wellington.
Ivy flowers are in globular clusters—umbels—where all the stalks originate from a single point.  This kind of inflorescence is common in the ivy family Araliaceae, and its related family Apiaceae.  It's also found in some unrelated plants, like onions and garlic (Alliaceae) and Agapanthus (Agapanthaceae).

The flowers have an unpleasant smell, and are visited by flies, bees, and wasps, and also some moths and butterflies.  Of these, Jacobs et al. (2009) concluded that wasps would likely be the most effective pollinators in England.
Ivy is an effective treatment for graffiti on this old wall in Kelburn, Wellingtom.
Ivy fruits are dispersed by birds, and they germinate freely.  The plants spread across the ground or climb up trees and buildings, attaching the stems by clusters of roots (G above).  These can weaken mortar on stonework and brickwork.  Fortunately, unwanted ivy on a tree or building is quite easy to deal with: cutting the stems at ground level will quickly kill them, but getting rid of the plant altogether isn't so easy.


Jacobs, J.H.; Clark, S.J.; Denholm, I.; Goulson, D.; Stoate, C.; Osborne, J.L. 2009. Pollinator effectiveness and fruit set in common ivy, Hedera helix (Araliaceae). Arthropod-Plant Interactions DOI 10.1007/s11829-009-9080-9

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