From a botanical perspective, the question of different types of English Ivy (Hedera helix) is addressed through the concepts of species, subspecies, cultivars, and growth phases. English Ivy is not a single uniform plant but a species with significant genetic diversity that has led to the recognition of distinct botanical varieties and, more commonly, a vast number of cultivated varieties selected for specific ornamental traits. Understanding these distinctions is key to appreciating the plant's adaptability and horticultural value.
Within the species Hedera helix, botanists have identified several subspecies that evolved in different geographic regions. These subspecies are genetically distinct and often exhibit subtle morphological differences, such as variations in leaf shape, size, and cold hardiness. For example, Hedera helix subsp. helix is the common type found throughout much of Europe, while Hedera helix subsp. poetarum is native to the Balkans and Italy, bearing orange-yellow berries instead of the typical black ones. Another, Hedera helix subsp. hibernica, is often called Irish Ivy and is known for its larger leaves and more vigorous growth habit compared to the standard English Ivy. These subspecies can interbreed, which further adds to the genetic diversity found in cultivated plants.
The most visible "types" of English Ivy to gardeners and homeowners are the numerous cultivars. These are plants selected and propagated by humans for specific desirable characteristics that are not necessarily found in the wild forms. Cultivars are propagated vegetatively (e.g., through cuttings) to maintain their unique traits. The diversity among cultivars is immense, primarily focusing on foliage. They can be categorized into several groups based on their leaf characteristics. Variegated cultivars, such as 'Glacier' (with silvery-gray and cream margins) and 'Goldchild' (with bright gold edges), are prized for their light-colored foliage. There are also cultivars with uniquely shaped leaves, like the bird's-foot-shaped leaves of 'Sagittifolia' or the curly, ruffled leaves of 'Ivalace'. Furthermore, growth habit varies, with some cultivars like 'Pittsburgh' being particularly vigorous climbers, while others, such as 'Needlepoint', have a more compact and slow-growing nature with small, fine-pointed leaves.
A crucial botanical distinction within a single English Ivy plant is its two distinct growth phases: juvenile and adult. This phenomenon, known as heteroblasty, represents a significant change in form and function as the plant matures. The juvenile phase is the climbing or creeping stage. During this phase, the plant produces stems with adventitious roots that cling to surfaces and displays the characteristic lobed leaves. This form is sterile and cannot produce flowers. Once the plant reaches the top of a support or sufficient maturity, it transitions to the adult phase. The adult growth is non-climbing, with stems that grow outward rather than upward. The leaves change shape, becoming unlobed, ovate, or diamond-shaped. Most importantly, the adult phase produces umbels of greenish-yellow flowers in the fall, which develop into black berries in late winter. This phase is essential for the plant's sexual reproduction.
Recognizing the different types of English Ivy has practical importance. From a horticultural standpoint, selecting the right cultivar for a specific purpose is vital. A variegated, slow-growing cultivar like 'Adam' is suitable for indoor containers or small topiaries, while a hardy, vigorous subspecies like Hedera helix subsp. hibernica might be chosen for quickly covering a large wall or for ground cover in a landscape. Furthermore, the growth phase is relevant for identification and control. The adult, flowering form can be mistaken for a different plant altogether, and it is the stage that produces seeds, contributing to its spread in natural areas where it may be invasive. Understanding that the juvenile clinging form will eventually morph into a flowering shrub-like form helps in managing the plant long-term in a garden setting.
