The most common living relative of the whale is the hippopotamus. Who would have thought that! Like whales, common yard trees growing in Denver have surprising botanical bedfellows or closest living relatives. Homeowners with a unique tree with interesting taxonomies, please contact us, and we will add it to the Strange Botanical Bedfellows blog.
Northern Catalpa (Catalpa speciosa)
The Northern Catalpa looks like a legume, but it is not. It is instead in the Bignoniaceae, or trumpet creeper family. Its close relative is the Trumpet Vine. The tree is a sure bet in Denver because it tolerates our alkaline soils and arid climate. On top of that, the tree is also disease- and insect-resistant. The tree’s large, heart-shaped leaves and height give it a distinct look, and its showy orchid-like flowers stand out. It is best known for its 8-12 inch legume-like seed pods.
Catalpa trees have an interesting relationship with the Catalpa Sphinx Moth. Their caterpillars, called Catalpa worms, are sought out by anglers because they are tough and stay active on hooks. Large infestations of these caterpillars can defoliate a tree, but these hardy trees recover quickly by producing new leaves.
Ginkgo Tree (Ginkgo biloba)
Like the Magnolia tree, the Ginkgo tree is a living fossil. Gingkos are in theGinkgoaceae family and are the evolutionary link between ferns and conifers. It remains the only surviving tree species that existed before dinosaurs roamed the earth. Most experts thought they were extinct, but Engelbert Kämpfer, a German scientist and physician working for the Dutch East India Company, found them in Japan in 1691. The tree he discovered had been brought to the island by Buddhist monks from China years earlier. Ginkgo trees live for a very long time. The picture above shows a 1,400-year-old tree growing at the Gu Guanyin Buddhist Temple in China. Some people call them maidenhair trees because their leaves resemble those of a maidenhair fern.
William Hamilton, a prominent attorney in Philadelphia, brought the first three ginkgos to Philadelphia, Pennsylvania, in 1785. That was a good move, consular, but bringing the Tree of Heaven (Ailanthus) to America was not so good. Click here to read our blog titled “The Tree From Hell.”
Ginkgos are tough trees, but they grow very slowly. They grow well in polluted urban environments. They make excellent accent trees in home landscapes. Ginkgos lose their leaves at the same time, leaving an attractive yellow ring around each tree. We recommend planting male trees because the females produce a foul-smelling fruit structure in the fall.
Kentucky Coffeetree (Gymnocladus dioicus)
The Kentucky Coffeetree is actually a legume and in the Fabaceae family. Legumes include food plants such as beans, peas, and lentils. The tree gets its name from Kentucky pioneers who thought the tree’s seeds resembled coffee beans. Its wood was used to construct railway sleepers in the 1800s. Experts disagree on whether their seed pods are edible. However, the seed pulp is toxic to cattle. The tree grows natively in rich bottomland soils of Pennsylvania to Nebraska and from Minnesota to Oklahoma.
Ross Tree recommends Kentucky Coffeetrees for planting because it is tolerant of pollution, drought, and Denver’s alkaline clay soils. They tend to be insect-free. Please note that the saplings tend to be ugly ducklings for several years and grow slowly. At maturity, they transform into beautiful trees, each with its own unique shape. Foresters across the county recommend these trees as replacements for Ash and Elms that are susceptible to insects and disease.
Honeylocust (Gleditsia triacanthos)
The Honeylocust is also a legume. Its relatives include Wisteria, Black Locust, Redbud, and Kentucky Coffeetree. The trees’ small, green, compound, ovate leaves turn yellow in the fall. Honeylocust flowers late in the spring, producing long, sometimes twisted reddish-brown legume seed pods. The trees have a feathered look and do a good job of filtering sunlight in yards. Most people plant thornless Honeylocust trees (Gleditsia triacanthos var. inermis).
In Denver, consecutive drought years make these trees susceptible to Thyronectria cankers. Homeowners need to remember that Denver has an arid climate and water their Honeylocust accordingly. Watering helps the tree’s natural defense systems to ward off fungal diseases. Unfortunately, once established, there are no cures for Thyronectria cankers, so it is best to be proactive.
Linden Trees (Tilia americana)
Believe it or not, the Linden trees are a cousin to the okra plant. The tree is in the Malvaceae family, which includes hibiscus, cotton, okra, and chocolate plants. What is there not to like about a tree related to chocolate that smells great in the spring? Lindens are prized for their pyramidal shape and their deep green, heart-shaped leaves that turn golden yellow in fall. These trees have few insect problems, tolerate our sub-zero winter temperatures, and alkaline soils. Lindens grow slowly and take some years to provide shade.
Oak Trees (Quercus)
Oaks are part of the Fagaceae beech family that produce nuts with a characteristic cup or husk structure. Oaks and other beeches have no surprising herbaceous cousins. The oak is culturally synonymous with strength, permanence, and deep time — several ancient cultures, like the Druids, worshipped it. Ironically, Oaks are not ancient. They are actually evolutionary newcomers. Oak evolution starts with the rise of angiosperms – flowering plants. Gymnosperms, such as Ginkgos and Conifers, produce naked seeds and are not pollinated. Flowering plants gained a significant competitive advantage by relying on bees and beetles for pollination, allowing them to produce more seeds than their competitors. Oaks spread across the globe quickly in evolutionary time, making them one of the most successful species on the planet. Charles Darwin called this “an abominable mystery.” Oaks and other hardwoods developed the ability to shed their leaves in the fall about 40 million years ago, as the Earth cooled. Abscission, the complex process that makes leaves drop in the fall, allows hardwoods to conserve water and go dormant during the winter months.
Ross Tree recommends planting hardy, drought-tolerant oaks that are adaptable to alkaline, clay soils. Top choices include the durable Bur, Gambel, and Chinkapin Oaks.
Maples (Acer)
Maples have an interesting taxonomy. In the early 2000s, dendrologists (tree scientists) using DNA research moved Maples from the Aceraceae to the Sapindaceae (Soapberry family). The berries of Soapberry trees contain saponins that lather like soap in water. Native Americans used them as a detergent. Horse Chestnuts and Buckeyes are the closest cousins to Maples. Thirteen Maples are native to North America. The Rocky Mountain Maple and the Boxelder are in the Acer family and are native to Colorado.
In older Denver neighborhoods, Silver Maples lined the streets in Congress Park, North Denver, Five Points, Washington Park, Country Club, University Park, and Bonnie Brae. These soft maples were popular 100 years ago because they grew fast and tall. Unfortunately, Silver Maples are susceptible to fungal infections. It is not unusual for a mature 75-foot Silver Maple to be hollow inside, making it unstable. The Denver Forester no longer recommends planting these trees in right-of-ways. Ross Tree recommends planting hard maples, such as Bigtooth, Sugar cultivars, and State Street. Norway Maples are considered invasive because of their excessive seed production and aggressive root systems.
Ross Tree has been servicing the Denver area since 1978. We love trees and are the go-to-company for complex tree pruning and removal jobs. Got a question or a tree problem? Call 303-871-9121 or click here to complete a service request form.
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