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Hollies (Ilex spp.)

HolliesHollies are familiar trees, easily recognized by their glossy, dark green foliage and beautiful bright red berries. But hollies are a diverse and varied group, and several species break from this mold. Although the vast majority of holly species are evergreen, a handful shed their leaves annually; some have spiny leaves, while others bear smooth, round foliage; and while bright red berries are iconic, some species bear yellow or black fruit.

Hundreds of species have been described worldwide, but a few – notably the American holly and European holly – are the most commonly used in ornamental plantings.

Wildlife Interactions

While holly fruits (technically, holly fruits are drupes, rather than berries) are toxic to humans and some domestic animals, a variety of wild creatures rely on them for a food source. Insects also feed on the nectar produced by holly flowers, and play an important role in fertilization.

Holly fruits develop from the late summer to the early winter, but most wild animals eschew the drupes until they’ve been through multiple freeze-and-thaw cycles. This appears to soften the previously hard fruits and make them more palatable.

In addition to providing value as a food source, hollies provide very dense cover to rodents and birds foraging amid their boughs. Nesting birds will also set up shop in these dense, often spiny, foliage.

Ornamental Use and Culture

Hollies are quite popular in the ornamental plant trade, and they are available as both wild-type plants and numerous human-created hybrids and cultivars.

Because most hollies are dioecious (plants occur as distinct male and female individuals), it is wise to plant representatives of both sexes to ensure the best possible fruit set. Additionally, while American hollies and a few other forms grow well in the shade, they will produce more fruit when grown in full sun.

Most hollies prefer well-drained, slightly acidic soils, but they are relatively flexible and will adapt to many different growing conditions. Different forms grow best in different places, and most locations have at least one species (typically many more) that will thrive in the area and climate. Taken collectively, hollies thrive in U.S.D.A. Hardiness Zones 3 through 11, which encompasses most of the country.

One down side to their ornamental use is the tendency of some to select non-native species. Most hollies, regardless of their point of origin, produce fruits that are attractive to local birds, who consume the drupes and deposit the seeds elsewhere. This often leads to the spread of invasive holly species, typically at the expense of native hollies and other understory species.

Selected Species Accounts

Species richness estimates for the genus Ilex vary widely. Some authorities recognize only 400 or 500 species, while others recognize nearly 800.

  • American holly(Ilex opaca) – The American holly is an understory species of the southeastern United States, which occasionally grows to about 60 feet in height. When they are grown in open areas with full sun, American hollies often become impressive, pyramid-shaped trees. However, like many other hollies, American hollies are slow-growing trees that take a decade or more to reach maturity. A number of cultivars have been developed, including dwarf forms that make excellent hedges.
  • European holly(Ilex aquifolium)– While European hollies are native to the warmer portions of Europe, their native range also extends into north Africa and southwest Asia.
  • Winterberry (Ilex verticillata)–Winterberry is a large (occasionally reaching 15 feet in height or more), deciduous shrub, native to the Northeastern United States. Celebrated for its glorious red fruit, which are especially conspicuous given the lack of winter foliage, winterberries are a favorite of gardeners. A variety of cultivars are available, with varying tolerance for soil conditions.
  • Mountain holly (Ilex mucronata) –The mountain holly was formerly called the false holly, and placed in the genus Nemopanthus, but recent molecular data has caused taxonomists to place it with the true hollies in the genus Ilex. A North American native, the mountain holly is a shrub that only rarely grows taller than 10 feet. It is sometimes grown as an ornamental shrub or in groups as a hedge.
Maidenhair Trees

Maidenhair Trees

Blessed with an impressive form, a hardy nature and unique leaves, maidenhair trees (Gingko biloba) are as attractive as they are interesting. With evolutionary roots extending deep into geological time, these leftovers of an ancient world have proven to be resilient survivors, who are even capable to thriving in 21st Century urban habitats.

Description

Though their branches often develop irregularly, maidenhairs typically achieve an aesthetically pleasing form. Maidenhair trees become quite large with age, sometimes surpassing 120 feet in height.

The distinctive bi-lobed leaves of maidenhair trees make them hard to mistake them for anything else. In fact, their specific epithet – biloba – means two-lobes (the name maidenhair refers to the species’ superficial resemblance to maidenhair ferns of the genus Adiantum).  As deciduous trees, maidenhairs shed their entire canopy each winter. However, before dropping to the ground, the leaves turn a beautiful shade of gold. Given their typically picturesque growth form, large specimens can be absolutely breathtaking in the autumn.

Maidenhairs are dioecious trees, meaning that individuals are either male or female. Female plants produce copious amounts of seeds that fall to the ground in the late fall or early winter. These seeds are covered with a foul-smelling seed coat, which many people find highly objectionable. The males produce no foul-smelling seeds, but they produce highly allergenic pollen.

Classification

As evidenced by their placement in the tree of life, maidenhair trees are some of the most unique organisms on the planet. Botanists consider maidenhair trees (Gingko biloba) to be the only living descendants of an entire phylum of plants.

To put this into some context, consider that every flowering plant in the world – from sunflower to redwood — is classified in the phylum Anthophyta. Scientists only recognize nine such groups (phyla) of living plants. Conifers form their own phylum, as do all ferns, horsetails, cycads, club mosses, gnetophyes and whisk ferns. And, as we said at the outset, maidenhair trees form their own phylum, called Gingkophyta.

Evolutionary Path

Maidenhairs had evolved by about 200 million years ago, and these ancient specimens strongly resemble the living species. Accordingly, many biologists call them “living fossils,” as they are living remnants of an ancient world. While some of the oldest maidenhair fossils exhibit a different form of seed attachment than living specimens do, those from about 65 million years ago are virtually identical to the modern form.

Culture, Cultivation and Cuisine

Maidenhair trees have played an important role in human culture, although this history only dates back about 1,000 years. People have grown maidenhair trees ornamentally for much of this time and harvested the seeds as a food source and for use in traditional medicine. Maidenhair trees are also popular subjects for the practice of bonsai.

Formerly found all over the globe, maidenhairs had virtually disappeared by about 2 million years ago. But before they could disappear forever, humans eventually found and cultivated some of these scattered survivors, thereby allowing the trees to be widely available in the modern world. The only known wild populations of the trees currently grow in a few Chinese localities.

Maidenhairs prefer forested sites, with well-drained, acidic soils, but they are highly adaptable trees that can live in a variety of habitats – including urban areas. Because they tolerate the indignities of city living, maidenhairs have become popular street trees, commonly planted throughout Europe, North America and Asia. Though they rarely escape cultivation in North America or Europe, they often become naturalized in parts of Asia.

Japanese Umbrella Pines

Japanese Umbrella Pines

The Japanese umbrella pine (Sciadopitys verticillata) is the single described member of its genus, and – as its name suggests – it is a Japanese endemic. While a popular ornamental that is grown in many locations around the world, they are considered sacred in their native range.

Description

Japanese umbrella pines are unusual-looking trees that rarely solicit lukewarm opinions – as explained by the University of Florida Extension Service, “people either love this tree or won’t even look at it.” The whorled tufts of evergreen needles found at the end of the trees’ branches are said to resemble umbrellas, hence the species’ common name.

Interestingly, these umbrella-like needles carry out photosynthesis, but are not “true leaves.” Instead, the trees’ true leaves occur as scaly, twig-hugging structures. The foliage of these trees is often quite dense.

Although the cones are not produced for some time, those that eventually appear are relatively attractive. They are about 3 or 4 inches long and become quite plump at maturity.

The bark of Japanese umbrella trees is very attractive, having a rich-reddish-brown coloration. Its texture is often described as “fibrous” or “stringy.” Upon cutting into the wood, one immediately becomes aware of the wood’s distinctive, spicy fragrance.

Growth and Longevity

Japanese umbrella pines grow very slowly and take several decades to mature. Growing to about 90 feet in height in their native lands, most umbrella pines remain much smaller – typically less than 35 feet tall – when planted elsewhere.

The largest and likely oldest living specimen is located near a temple in the town of Nodagawa. The temple’s records indicate that the tree has been growing at the site for the last 700 years.

Evolutionary History

Although a member of the same order that contains living pines and spruces, the Japanese umbrella pine has no close relatives in the modern world. Japanese umbrella pines were originally classified within the family Cupressaaceae, but they have recently been moved to their own family, the Sciadoptiyaceae. This unusual conifer is a relic from an ancient time; researchers have collected fossil remains of these trees that are approximately 230 million years old. In fact, the species represents one of the oldest living conifer taxa in the world.

Extinct relatives of the species probably grew across vast expanses of North America, Europe and mainland Asia. Additionally, the trees probably played a more important ecological role in the Mesozoic Era than they do in the modern world.

Culture and Commercial Uses

Japanese umbrella trees are shade tolerant, but they grow best in partial to full sun. They grow best in USDA Hardiness Zones 4 and 5, although some authorities list them as hardy from Zones 3 through 7. Several cultivars of the species are available commercially, including a weeping form and a dwarf form, which only reaches about 10 feet in height.

While these trees require well-drained soil and have relatively modest water requirements, they are most common in humid cloud forests within their native range. These hardy trees are also resistant to most pests and pathogens, making them relatively low-maintenance trees. While these trees are most common among gardeners and landscapers, some bonsai practitioners utilize these attractive conifers.

The wood of Japanese umbrella pines is water-resistant; so many boat makers use it in ship construction.

Cycas

Sago Cycad and Their Relatives

Trees of the genus Cycas are primitive gymnosperms that superficially resemble palm trees. However, they are quite distinct from true palms, and form an entirely different lineage.

Description and Identification

Cycas trees – like most other members of the class Cycadopsida – feature a ring of pinnately compound (feather-like) leaves attached to the top of the trunk. You can further recognize members of the genus by noting the prominent mid-ribs of the leaflets and lack of any obvious secondary veins.

Like all other cycads, trees of the genus Cycas are dioecious, with distinct male and female plants. In both cases, the cones lie at the top of the trunk and emerge from the center of the leaf ring.

While some members of the genus feature round, subterranean trunks and are essentially shrub-like, others have tapering, tree-like trunks that grow aboveground. Most cycads feature relatively shallow root systems and grow very slowly. The majority of species remain rather small, with the largest specimens reaching perhaps 35 to 40 feet in height.

Relatives and Relationships

Between 90 and 115 species comprise the genus Cycas (the only genus in the family Cycadaceae), making it one of the largest lineages in the class Cycadopsida. Commonly known as the cycads, the ancestor of this group of species is thought to be the sister lineage to the other families in the class.

Cycads are ancient species that were found across most of the world by the beginning of the Triassic period. In fact, the entire Mesozoic era (which spanned from approximately 225 million years ago to 65 million years ago), is often called the “Age of the Cycads,” because of the plants’ dominance in these ecosystems. According to the University of California, Museum of Paleontology, cycads represented one-fifth of the world’s flora during much of the Triassic and Jurassic periods.

Habitats and Geography

Cycas trees are confined to the Old World. They are found from Japan, west to Africa and Madagascar, and south as far as northern Australia. As a group, the trees inhabit a variety of landscapes; some forms grow in tropical rainforests, while others grow along rocky escarpments.

Some species, for example, Cycas circinalis are well adapted to living along shorelines. The seeds of these trees are buoyant and capable of lasting extended periods of time floating through the ocean, until they eventually wash up in a habitable location.

Culture and Uses

One of the most commonly cultivated species is the so-called sago palm (Cycas revoluta). It prefers full sun, but some people succeed in growing them indoors. Because they remain relatively small, they are often planted in restricted spaces. If provided with a suitably large vessel, sago palms often thrive when grown in a container.

Several indigenous cultures throughout the range of these plants collect and eat the trees’ seeds as a food source, and some harvest starch – called sago — from the stems. However, neurotoxins are found throughout many different portions of the plants; if consumed, the poisons can cause serious disease or death. Accordingly, most people who eat the seeds or sago attempt to leach out the toxins with copious amounts of water.