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Hedera

life science Maturity 5-7 Next article →

Hedera is a genus of evergreen plants that includes 12 to 15 different species. These plants are woody and can either creep along the ground or climb upward. They belong to the family Araliaceae. Most species are native to regions like Western and Southern Europe, North Africa, and parts of Asia reaching as far as Japan and Taiwan. Because they stay green year-round, they are frequently used as ornamental plants to cover walls, fences, or tree stumps.

Hedera helix Leaves 3008px
Hedera helix Leaves 3008px

The way ivy grows changes significantly depending on its environment and age. On level ground, the plants remain low, typically only 5 to 20 cm in height. However, if they find a surface to climb, such as a tree or a rock face, they can reach at least 30 m above the ground.

Hedera climbs on a pine tree
Hedera climbs on a pine tree

The plant uses two distinct growth forms. Juvenile stems are slender and flexible. They use small aerial roots to attach themselves to a substrate like bark or stone. As the plant matures, it develops adult shoots. These shoots are thicker and self-supporting, meaning they do not require those small roots to stay upright.

Leaf shape also shifts as the plant moves from its juvenile stage to its adult stage. Juvenile leaves are palmately lobed, which means they have several points or lobes. When the plant reaches its adult stage and grows into sunny areas, it produces unlobed, cordate leaves. Cordate leaves are shaped like a heart. This transition occurs when the stems reach fertile flowering areas, usually at least 2 m above the ground.

Hedera canariensis Gomera
Hedera canariensis Gomera

These adult stems produce greenish-yellow flowers in clusters called umbels during the autumn or early winter.

Taxonomists categorize these species using several scientific details. One major way to group them is by the structure of their trichomes. Trichomes are tiny hairs found on the undersides of the leaves. Some species have scale-like trichomes, while others have stellate trichomes, which are star-shaped.

Hedera algeriensis 01
Hedera algeriensis 01

Species also vary in their chromosome numbers. While the basic diploid number is 48, some species are tetraploid with 96, hexaploid with 144, or even octaploid with 192 chromosomes. This genetic variety helps scientists understand how the different species are related.

The evolutionary history of Hedera suggests it originated in East Asia. The earliest known fossils of the genus were discovered in Korea and date back to the Oligocene epoch. From there, the genus expanded westward. It eventually reached Europe during the early-middle Miocene epoch.

Hedera algeriensis 01
Hedera algeriensis 01

Over time, many species have become allopatric, meaning they live in different geographic areas. Some species have even been known to hybridize. For example, a garden hybrid called × Fatshedera lizei was created in France in 1910 by crossing Fatsia japonica with Hedera hibernica.

Ivy plays a vital role in many ecosystems by providing food and shelter. The flowers are rich in nectar, which attracts many pollinators. The ivy bee, Colletes hederae, is completely dependent on these flowers for its entire life cycle.

Gwenyn ar Flodau Eiddew - Bees on Ivy Flowers - geograph.org.uk - 547757
Gwenyn ar Flodau Eiddew - Bees on Ivy Flowers - geograph.org.uk - 547757

In late winter or mid-spring, the plant produces berries that are greenish-black, dark purple, or sometimes yellow. These berries contain one to five seeds and are eaten by birds like thrushes and woodpigeons. As the birds eat the fruit, they disperse the seeds to new locations. Additionally, the dense, woody tangles of ivy provide nesting sites for birds and small mammals, as well as homes for many invertebrates.

While ivy is useful, it can also cause problems in certain environments. In North America, some ivy species are considered invasive exotic species. They can grow very quickly through underground rhizomes and above-ground runners. This allows them to smother native vegetation in forests and woodlands.

Hedera climbs on a pine tree
Hedera climbs on a pine tree

In Europe, the impact on trees is usually minor, though heavy growth can sometimes lead to windthrow damage. However, in North America, aggressive ivy can overwhelm a tree's ability to perform photosynthesis or maintain structural strength. Finally, users should be aware that the berries are moderately toxic to humans, and the foliage contains substances like falcarinol, which can cause skin irritation.

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🖼️ Images & Media (6)
File:Ivy fruits.JPG
Ivy fruits.JPG
File:Hedera canariensis Gomera.jpg
Hedera canariensis Gomera.jpg
File:Hedera algeriensis 01.jpg
Hedera algeriensis 01.jpg
File:Gwenyn ar Flodau Eiddew - Bees on Ivy Flowers - geograph.org.uk - 547757.jpg
Gwenyn ar Flodau Eiddew - Bees on Ivy...
File:Hedera helix Leaves 3008px.jpg
Hedera helix Leaves 3008px.jpg
File:Hedera climbs on a pine tree.jpg
Hedera climbs on a pine tree.jpg
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