Read an Excerpt
Quiver Trees, Phantom Orchids & Rock Splitters
The Remarkable Survival Strategies of Plants
By Jesse Vernon Trail ECW PRESS
Copyright © 2015 Jesse Vernon Trail
All rights reserved.
ISBN: 978-1-77090-704-1
CHAPTER 1
POLLINATION AND ATTRACTING POLLINATORS
Flowers, despite their beauty, are above all utilitarian: their primary purpose is to produce seeds. Some basic botany in a nutshell: the plant produces flowers; the flowers are pollinated by a pollinator; the flower is fertilized; the flower then produces seed; the seed is spread; the seed germinates and develops into a new plant; and voilà, the species lives on.
The sex life of plants resembles that of most of the earth's creatures, as the male pollen is transferred to the female receptive or reproductive organs, including the flower's ovary. It's a cycle that repeats over and over, with new flowers emerging from the new plants. And there is a reward for the pollinator, who is gifted with food nectar and protein-rich pollen, which benefits bees and some other creatures as well.
Our focus here is on the flowering plants, angiosperms, though similar processes occur among other plants as well. Flowering plants have developed some fascinating survival strategies to ensure that their flowers are attractive to potential pollinators. Many plants produce sweet nectar in their flowers to attract creatures, while other plants use fragrance as a lure. Still others rely on color or wonderful shapes to attract their visitors — or any combination of these strategies.
In some instances, the flowering plant and the pollinator become partially or fully dependent on each other. In other instances, wind, water and other means achieve the pollination requirements. In the cases of plants such as holly, each plant is either male or female. For such dioecious plants, both sexes have to be in the vicinity of the other. If not, pollination, fertilization and seed production cannot take place. Other plants, meanwhile — monoecious varieties — have both male and female flowers. The majority of flowering plants, however, have both sexes (stamen and pistil) within each flower, but pollination must be transferred from one flower to the next for fertilization to occur.
Of course, we humans also benefit from these fascinating processes. Think of the exquisite aroma of a rose, a spectacular vista of vividly colored flowers carpeting the landscape or the intricate shapes and colors of a passion vine. We even enjoy the activities of the pollinators and the entire flowering process.
Let's begin by focusing on the remarkable process of pollination and explore some of the main pollinators and their often special relationships with flowers.
INTRODUCING the POLLINATORS
BEES and WASPS
Bees are immensely important in the pollination of a great many flowering plants. They are virtually indispensable when it comes to the majority of our food crops, not to mention animal life. Thus it is a matter of great concern that many bee species are under threat and face possible extinction. This would be a severe blow not only to mankind, but also to a tremendous number of animals, insects and plant species as well.
All bees are partial to flowers in the blue, purple and ultraviolet shades that dominate one end of the color spectrum, but bumblebees find blue flowers especially attractive. Scientists have determined that bees see a broader portion of the color spectrum than we do. They may well see a pure white flower as having a vivid, highly attractive color we cannot see, which is perhaps why they are also strongly drawn to white flowers.
The relationship between certain species of orchid — especially Ophrys — and bees is special. Each flower has the almost uncanny appearance of the shapely body (from a bee's perspective) of a female bee. Male bees are duped by the perceived potential for sex. As if this is not enough, these orchids also exude a perfumelike scent that simulates the pheromones produced by receptive female bees. The male bees are either very slow learners or enjoy the experience, since they continue on to the next flower.
Many of these mimicking orchids target specific bees, wasps or other insects to ensure pollination of their flowers. For example, carefully observe the British bee orchid, O. mellifera, and the yellow bee orchid, O. lutea, and you will see the close similarity to the female bee or other insect being mimicked. However, there is a danger to the plant in targeting specific insects: without the presence of this particular insect, pollination of the orchid would not take place and the very existence of the species would be in great peril.
The grasslands of central England provide one habitat for the bee orchid, Ophrys apifera. Notice the flower's intricate design looks very similar to a female bee. When the male bee lands, he grasps on to the thick velvety maroon-and-yellow lower lip of the flower in an attempt to copulate with it. In the process, the upper flower above the bee dusts the bee's head with pollen. The bee then carries this pollen to the next flower, where the pollen is received, and pollination is successful.
Instead of using mimicry, other plants, such as Catalpa speciosa, have intricate designs on their flowers that act like a flight-landing platform to guide a bee or other insects to their nectar and pollen. Each of this tree's flowers has a broad lower-lip landing pad, inviting the insect to its nectar with markings of orange lines and rows of purple dots.
Many of us are unaware of the great distances that bees travel in a single day to collect nectar and pollen from flowers. Some will even travel high into the Himalayan mountains to dine on the nectar of densely woolly Saussurea gossypiphora and S. sacra. Weary after a hard day's work, bees often find refuge from the extremely cold mountain nights in these particularly accommodating plants. Several species of Saussurea are so furry that bees can cozy up deep inside, where the flowers are, and stay overnight in the warmth of their shelter. The plants even provide a small opening at the top, allowing the bees to enter and reach the flowers — it's deluxe hotel accommodation for the bees.
By covering themselves with downy hairs, several Saussurea species are better able to endure the harsh conditions found in the Himalayas. Often, the plants are so densely woolly that it is difficult to distinguish the leaves within the mound of fur that provides the ultimate in insulation.
HUMMINGBIRDS and OTHER BIRDS
Of all the birds that pollinate flowers, hummingbirds are among the most amazing. For such tiny birds they move incredibly fast, and when they hover to sip sweet nectar from a flower, their rapid wing beats are but a blur. Many species of hummingbird are also quite colorful, which only adds to their appeal. By flitting about from flower to flower, they are very efficient pollinators of several different flowering plants, and in return hummingbirds find a good source of sweet food nectar.
Hummingbirds are some of the best pollinators for flowers with long floral tubes, such as the flowers of the trumpet vine. Nectar is often accessible only by birds or insects with long proboscises like those of our hummingbirds. Reds and oranges are especially attractive to hummingbirds, as these birds see more toward the red end of the color spectrum. Hummingbirds have a poor sense of smell, so flower fragrance is not a factor in attracting them.
High on the slopes of the Andes Mountains in Colombia, we can feel the coolness of the moist air, as well as see the thick fog all around us. Among the dense green foliage of the forest lives an extremely rare, nearly extinct, exquisitely beautiful species of passionflower vines, Passiflora parritae. Climbing by tendrils high into the trees, this vine bears a profusion of large upside-down hanging clusters of bright orange flowers in August and September.
The sole pollinator of this magnificent passionflower is the tiny sword-billed hummingbird, Ensifera ensifera. It is also the only bird on earth with a bill longer than its body, excluding the tail. Mainly because of global warming, this hummingbird is being forced to even higher altitudes, leaving the passionflower without its pollinator. The hummingbird might still survive by sipping on the nectar of other flowering plants higher up the mountain slopes, but the passionflower is faced with possible extinction. Even propagation attempts to save Passiflora parritae have failed. There is, however, one known specimen in cultivation in the San Francisco Botanical Garden at Strybing Arboretum. If you are ever in the area, do pay it a visit.
In a starkly different climate, the hot fynbos of the South African Cape in summer is home to the magnificent and often colorful large flowers of Protea species and their main — in some circumstances exclusive — pollinator, the Cape sugarbird. The King protea, Protea cynaroides, is South Africa's floral emblem. It is a medium-sized woody shrub with leathery green leaves, but it is its flower that is most incredible for its intricate structure. Each of the many flower heads of these striking plants is huge. The dense, clustered central zone is white, cream or yellowish, surrounded by showy bracts (modified, often showy leaves accompanying flowers) that vary in color from deep crimson to shades of pink.
The protea flowers are perfect for the Cape sugarbirds, supplying them with plenty of sweet nectar in return for their pollination service. Sugarbirds are gray-brown with a spot of bright yellow under their tails, and the males have impressively long tail feathers. A long sharp beak with a long rough-tipped tongue allows the birds to reach the rich nectar of the protea.
There are many more examples of hummingbird and other bird pollinators, but these two demonstrate the strong relationships that can exist between flowering plants and birds.
BUTTERFLIES and MOTHS
Like the bee and the hummingbird, the butterfly and the moth also have a proboscis to sip the sweet nectar of flowers. Butterflies, for the most part, are out and about during the daylight hours, whereas the moth, depending on its species and the species of plant being visited, may feed only at night. Like bats, evening- and night-feeding moths are most often attracted to flowers with a strong fragrance. The flowers of these plants are usually a pale color or white.
Just a small sampling of some of the better-known butterfly- and moth-pollinated flowering plants include butterfly bush, Buddleia davidii, and milkweed, Asclepias, visited often by specific butterfly species. Evening star, Mentzelia decapetala, and certain species of queen of the night, such as Hylocereus and Selenicereus, open their flowers only after sundown and often to attract a particular moth pollinator.
Certain species of succulents and cacti of arid regions have exclusive symbiotic relationships with specific moths. For example, only yucca moths can pollinate yuccas, and yucca flowers are the sole source of food for the moth larvae. Amazingly, there is one species of moth for each species of yucca. The yucca moths lay their eggs in the yucca flowers and in the process collect pollen that they transfer to the next flower, and so on. The developing moth larvae feed on both the nectar and, as they get older, some of the maturing seeds as well. There is no danger of all the seeds being eaten, as hundreds of seeds are produced; many seeds remain for later dispersal to start new plants. Adult moths, in return for their pollination service, get food from the abundant nectar in the yucca flowers.
BATS
Bats are nocturnal creatures that feed mostly on insects, but they also supplement their diets with the sweet-tasting, nutritious nectar of certain evening- and night-blooming flowers. Bats cannot see very well, so the best way for a flowering plant to attract bats is with strong fragrance and/or large, easily accessible flowers, rather than flower color.
Found in an arid region not far from the central coast of Mexico, the strongly fragrant century plant, Agave americana, is prized by bats and humans when in bloom. Virtually all agaves are monocarpic, meaning they die after a single flowering, but when they do bloom, it is a spectacular display. From the familiar agave stemless rosette of spiny gray-green or bluish-green tapered leaves grows a huge flower stalk with symmetrical branching. Yellowish-green to bright yellow flowers cluster at the end of each branch. Wildlife feed on the century plant's copious nectar during the day, but one of the plant's main pollinators, the fruit bat, visits at night, darting quickly from one flower to the next, ensuring the transfer of pollen.
The tropical Monteverde cloud forest region of Costa Rica is home to the bat-pollinated Mucuna vine. It bears long rope-like stalks that hang below the forest canopy, where night-flying bats can easily access its deliciously fragrant blossoms. These pea-like flowers in large dense clusters are often brilliantly colored in reds, yellows, purples and more, depending on the species.
Other night-blooming, bat-pollinated flowering plants include the organ pipe cactus, Stenocereus thurberi, with its long, tubular musky-scented flowers; the Arizona saguaro cactus, Carnegiea gigantea; and various species of the queen of the night.
FLIES
We don't often think of pollinators beyond those essential Bs: birds, bees, butterflies and bats, but other insects have a role to play as well. Flies, for example, are often attracted to flowers emanating the stench of rotting meat or other unpleasant smells. Two prominent examples, both from Southeast Asia, are the giant flowers of Rafflesia arnoldii and the titan arum, Amorphophallus titanium. The Rafflesia and related genera and species, such as Stapelia and Hoodia, take aroma to the most extreme level of repulsiveness. Several species also have the coloring and marbled patterns of fatty, rotting meat. Sounds and smells delicious — but only to a fly, that is! (Keep in mind, though, that many flies are also attracted to more pleasant scents.)
Rafflesia arnoldii has the largest single flower in the world. Each flower can measure up to 3 feet in diameter. Often referred to as carrion flowers, a common name shared by the other related genera and species, Rafflesia arnoldii are parasitic on nearby host plants and can be seen only when in bloom; otherwise the plants are hidden beneath the soil surface.
Another similar plant you might not want in your garden can be found in the forests of southern France. The Aristolochia rotunda's solitary, long, upright, tubular flower is a greenish yellow, with a distinctive maroon to deep purple upper flap. Its stench lures the flies inside, and they crawl down the flower tube. The inside of the tube has long downwardly directed hairs that are dense at the base to prevent the flies from crawling out. After a day or so confined inside the flower, the struggling flies become covered with pollen and are allowed to escape when the plant's tubular hairs loosen. Fortified by nectar, the insects fly off and pollinate the next flower they visit.
EXPLORING OTHER MEANS of POLLINATION
WIND and WATER
Hay fever and allergy sufferers are well aware of wind-pollinated plants and when and where their pollen is in the air. Wind-pollinated plants include beech, birch, elm, poplar, goldenrod, oak, hazelnut, nettle, walnut and pine. Grass family members are usually wind-pollinated as well. In each case, it is the male flowers that produce the often copious amounts of pollen to be transferred by air. But pollen transfer by bees and other creatures is a much more direct and efficient process than the random dispersal by wind.
In the Northern Okanagan Valley of British Columbia in spring, the ground can become carpeted by the bright yellow pollen of tall ponderosa pines, Pinus ponderosa. It is beautiful to see, and it also demonstrates the huge amount of pollen these pines need to produce to increase the chances that female flowers will receive the pollen.
Most aquatic plants are water-pollinated, producing a large amount of pollen to drift on the water currents. Again, much of the pollen is wasted.
SELF-POLLINATION
With a small number of flowering plant species, self-pollination can occur, thus circumventing the natural sex life of plants. But this is far from the norm in the plant world — and some would even say it's an unnatural occurrence. When it does happen, it is often a reaction to environmental circumstances or a lack of pollinators in the area over time.
(Continues...)
Excerpted from Quiver Trees, Phantom Orchids & Rock Splitters by Jesse Vernon Trail. Copyright © 2015 Jesse Vernon Trail. Excerpted by permission of ECW PRESS.
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