Ivy flowers. Macrophotograph of a cluster of immature ivy flowers. Each of the unopened flower buds contains five petals, five stamens and a single pistil. Ivy (Hedera helix) is an evergreen climber that parasitises trees, using sucker-like roots to cling to its host. Its small, yellowish green flowers develop in late autumn and are pollinated by wasps and flies. Each flower produces a single black berry, poisonous to humans but palatable to birds.