Plant Wonders--10 Tropical Plants Not to Miss

Looking into the Costa Rican rainforest

Ew! The tropics! Deadly snakes and poisonous plants! I tip-toed through the vegetation as if every leaf would bite!

I first encountered the tropics in 1973, when I took an Organization for Tropical Studies course, Tropical Ecology, which introduced U.S. graduate students to the tropics, in Costa Rica. At the beginning of the course, they gave us a safety orientation: these snakes are poisonous, these ants have a sting that will incapacitate you, these leaves cause welts...

Suitably intimidated--having experienced only the northern United States--I stayed in the middle of the path and tried not to get close to the leaves.


By the time the course was over, I had learned that, yes, there were dangerous animals and plants, but I had also learned perspective: the tropics are highly diverse, so there were also many more non-dangerous animals and plants than back home in Ohio.

And the diversity was full of marvels!

I have been to Costa Rica four times since that first trip, and to tropical countries all over the world as well. Here are 10 plants I treasure and always look for:

1. Sensitive Plants (Mimosa pudica, pea family, Fabaceae). When touched, the leaves close. The first photo is before I touched the palnt, the second picture, after. I'm a kid when it comes to the sensitive plant: I love touching the leaves and watching them close! The function is undoubtedly to protect the leaves, perhaps to make them less visible to a grazing animal or to reduce the surface area that is stepped on. Furthermore, the stems are thorny and with the leaves closed, less pleasant to bump.

sensiitive plant, Mimosa pudica

sensiitive plant, Mimosa pudica

2. Ant-plants: For example, the ant-acacia (Vachellia spp., formerly Acacia, pea family Fabaceae), cecropia (Cecropia spp., nettle family, Urticaceae) and others. These are plants which by various methods provide nesting places for ants. The thorns of ant-acacia, shown below, are hollowed out by ants who then disperse their colony throughout the tree. On cecropias the ants live in the plant's hollow stems. In both cases, if you bump the tree, the ant colony is disturbed and ants come pouring out to defend the plant. The cecropia ants are small, so while they probably mean you ill, they don't hurt. The acacia-ants are bigger and when they bite and sting, it is painful enough that everyone quickly learns to recognize and watch for ant-acacias. It is one of the perils of the forest.

ant-acacia, Vachelllia sp. 

In both cases housing ants works well for the trees: the ants keep the trees free of vines and plant-eating insects. Ant-plants are confined to regions without frost, since cold will kill the ants in their aerial nests. Ant-acacias are mainly found on the Pacific Coast of Central America, from Mexico to Costa Rica, cecropias are more widely distributed in disturbed areas of rainforests in both Central and South America. There are other ant-inhabited, ant-defended plants in the American tropics and across the Old World tropics, these are the two I know best.

Cecropia sp.

3. Strangler Figs (Ficus spp., fig family, Moraceae). Figs, the fruits, are attractive food for birds as well as humans. The tiny seeds of strangler figs fall in bird droppings high in the trees of a tropical forest. There, way above the ground, the seeds germinate and the fig begins to grow. Its roots grow down toward the earth, its shoots grow up toward light. Both twine around the host tree for support. If things go well for the fig, it will reach out into light above the host tree and root into the ground. Its strong stems and roots, ever increasing, gradually tighten around the host until it cuts off circulation and the host tree dies."Strangler fig" indeed.

strangler fig wrapped around host tree

4. Hummingbird Flowers: Hummingbirds are found only in the Americas. Costa Rica has 54 species of hummingbirds, large to very tiny, red, green, blue... (see images). Dozens of plants have flowers adapted to being pollinated by hummingbirds. I like the bright red flowers or bracts that attract hummingbirds and the wonderful whirring activity of hummingbirds visiting flowers.

hummingbird flower, Erythrina

Notice that they have narrow tubular flowers and stick out from/above the plant. The narrow shape keeps other animals from easily stealing the nectar that is offered to hummingbirds. The position outside the plant makes it easy for hummingbirds to hover while drinking nectar. (Meanwhile the plant sticks its pollen on the bird, which the hummingbird then carries to the next flower).

hummingbird flower

The plants I recognize as "hummingbird flowers" are just a few of the plants pollinated by hummingbirds: hummingbirds are smart and willing to try diverse flower shapes (see flowers in the link) (I think a few of the photos in the link are "bird-next-to-flower" not "bird-pollinating-flower." Photographers like hummingbird photos, and those are almost always made better by including a flower, but some photographers are happy to include a flower the hummingbird was not visiting just passing by.)

hummingbird flower: bract with open flower (upper right)

hummingbird flower, bract of Heliconius sp.

I called these last two "hummingbird flowers" and that's a bit misleading. The big red parts of both plants are bracts. Bracts are modified, bright colored leaves that function in pollination by making a big display. The actual flowers are relatively small, develop inside the bract and stick out when open (in the last photo, you can see the actual flower as a protrusion on the right). A benefit of showy bracts is that the complex of bracts produces flowers for weeks or even months. Hummingbirds quickly learn to come by every day and check for newly-opened flowers within the bract. Reliable food is very important for a high-energy flier such as a hummingbird.








5. Bananas (Musa spp., banana family, Musaceae). Bananas grow 25' tall, but they are monocotyledons, more closely related to grasses than to any tree. The stem is not wood, but tightly compressed leaf bases. Native to Southeast Asia, they were long ago introduced to the New World tropics, and, as a productive and popular fruit, you can find them growing in backyards (and front yards) throughout tropical America. If you've seen them, you know the fruit grows "upside down;" the first time you see it, it seems remarkable. Also impressive is the size of banana leaves: to 9' long, 2' wide. 

banana 

banana fruit and flowers

6. Coconuts (Cocos nucifera, palm family, Araceae). Like bananas, coconuts are not native to Costa Rica. They originated in the tropical Pacific Ocean and were unknown in the Atlantic before European exploration. The large seeds contain both clean water and food and store well, so they were quickly carried all over the world,. Today they are common and familiar plants on beaches worldwide. Familiarity shouldn't breed contempt: coconuts are wonderful plants! Not only are there many uses of the seeds, the leaves and stems are used as building and weaving material. (See my blog on Coconuts)  Like bananas, coconuts are big monocotyledons: tree-sized but with stems from compressed leaf bases, not wood.

Coconuts are also dangerous: falling coconuts have killed people.

coconut palm

coconut, with camera case for scale

7. Morning Glories (Ipomoea spp., morning glory family, Convolvulaceae). Morning glories are most diverse in the American tropics. (A few are found in tropical Asia and Africa, even fewer grow in places with distinct winters). The flowers of most species open at dawn and fade in the heat of the day, lasting only the one day. Many species have blue or purple tubular flowers that make adramatic splash of color at the edge of the tropical forest, gone by lunchtime. I loved their big bright flowers.(previous post on morning glories)

morning glory

morning glory, Ipomoea sp.

8. Passion Vines (Passiflora spp., passion vine family, Passifloraceae). A mainly American group, passion vines are diverse and very distinctive. The flowers have elaborate structures that led Christian missionaries to see religious symbols in their shape, leading to the name passion vine (passion of Christ). The fruits are interesting--the one in the picture below has a net around it--and in many cases edible (making, for example, passion fruit jelly). The leaves have quite variable shapes, sometimes within the same plant, and they climb with tendrils.

passion vine, Passiflora species

flower of another species of passion vine 

9. Orchids in Trees (orchid family, Orchidaceae). There are more species of orchids than of any other plant family, 27,800. Most orchids are uncommon: only for a few species will you ever find a field of orchids. In addition, many of the tropical species are epiphytic, growing on trees but not as parasites. They get both the water and nutrients they need from the air, which is only possible in moist tropical regions. Many species have small flowers in quiet colors like white and pale yellow, while others are very brightly colored. Flowers can be simple or weirdly-shaped. In nature, many orchids flower only infrequently. Putting all those things together, seeing wild orchids in flower is always a treat. My pictures are poor because I have few to choose from and because photographing a plant over my head in partial shade is tricky. (In the second picture, I think the plant is or was tied up on the tree, but it gives the idea of how they grow. Watch for them!)

flowering orchid

orchid leaves

10. Bromeliads in Trees (bromeliad family, Bromeliaceae). The bromeliads are a group of about 3500 species of which more than 90% are found only in the American tropics. The majority of bromeliads are epiphytic, growing on trees. They are the clumps of leaves along the nearly leafless branches in the first photo below. Many have big bright flowers. Like epiphytic orchids, ephiphytic bromeliads are confined to regions with high humidity and little or no frost.

bromeliads

bromeliad flowering in a tree

You don't have to go to Costa Rica to see these marvelous plants--they can be found throughout tropical America. Tropical Asia and Africa have equivalent wonders. But my first encounter with tropical plants was in Costa Rica, so I know they are all there.


Comments and corrections welcome!



References
More about bananas: http://homeguides.sfgate.com/tall-banana-tree-54933.html

Kathy Keeler

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