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February 7, 2010 | Nick Daniel, Horticulture Specialist, Cactus & Succulent Collection

What makes a tropical plant a tropical plant? This is a question I have been asked several times, and it may sound like it's an easy one to answer, and sometimes it is, but today, I'm going to dive a little deeper. It would be easy for me to just say, "A tropical plant is any plant found between the Tropic of Cancer and the Tropic of Capricorn", and this is true, but way too simple of an answer for such a complex question. Tropical plants do not just come from rain forests, the tropics have alpine ecosystems, desert, evergreen forests, seasonal forests, rain forests and everything in between. The tropics have such a great biodiversity, and not just plants, but all living things, climates and ecosystems are represented in the tropics. It is sometimes easy to forget that the Sahara Desert is just as tropical as Costa Rica!

Did you know that a little over 2/3 of the world's plant species are found in the tropics? Not to discredit our lovely and unique Colorado/Rocky Mountain native plants, but, wow! Nearly every family one could think of has genera or species represented in the tropics. The tropics are well regarded as some of the most beautiful and widely visited/lived in areas of the world, but sadly, plant, animal and microorganism species are disappearing before we can even classify them.

Here are some statistics regarding the world's rain forests (which are primarily found in the tropics): Rain forests once covered 14% of the earth's surface and it is now estimated that they only cover 6%, and within the next 75 years, they may cover 0%. One and a half acres of rain forest are destroyed every minute; every two and half acres of rain forest may contain over 1,500 higher plants! And this is just the rain forest, remember, the tropics cover a very large swathe of land beyond just rain forest.

Why grow tropical plants in Denver, Colorado? Good question, I could write for days on why tropical plants should be grown in Denver, but I'll narrow it down for now. Many famous Colorado landscape plants are from the tropics, a great example is Delosperma or the ice plant. You won't see it in the Boettcher Memorial Tropical Conservatory though, you'd have to venture out to South African Plaza to enjoy these beauties, because not all tropical plants are humidity-loving, water-crazy rain forest species. There are many, many Colorado hardy tropical plants, so next time you are picking out plants for your garden, consider their origins!

Our collection of tropical plants here at the Denver Botanic Gardens is very unique and impressive (now I'm referring to our humidity-loving, water-crazy beauties). Many of the plants we grow with wet forest origins have medicinal properties, food uses and a plethora of other ethnobotanical applications. Some of them are endangered and some of them may disappear in the wild in our lifetimes, if this isn't reason enough to grow tropical plants in Denver, then I'm not sure what is. It is just too easy being from Colorado with all of our great natives to dismiss tropical plants just because we can't grow them outside, but please, understand the importance of maintaining this collection. These are not plants that one could just go to Rocky Mountain National Park to enjoy, and some of them, you'd be hard pressed to even see in their tropical origins. And again, I am not trying to discredit our native plants or any non-tropical plants in general, I just feel that it is important to appreciate the tropical plants just as much as any other plants displayed at the Denver Botanic Gardens, after all, many of us grow tropicals in our homes.

Yes, I digressed slightly from my original topic, I guess I just get a little passionate about my tropical plants. In the near future, I will have a 'Let's Talk Tropics' follow-up with more nitty-gritty down an dirty plant science talk, so that the concept of "tropical plants" can really get hammered down. So, next time as you are strolling through the Denver Botanic Gardens enjoying the beauty and education presented to you, be sure to ask questions, pick a couple of plants and research their origins, you will be shocked to discover how many of our plants outside of the Boettcher Tropical Conservatory have tropical origins!


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