Cardinal Flowers are to Ruby-throated Hummingbirds what Goldenrod is to Honey Bees in the fall — an important source of nutrients just when it’s needed most. Just as hummingbirds are preparing for their migration south and nearly doubling their weight (from about 3.25 grams to 6 grams) before crossing the Gulf of Mexico, Cardinal Flower blossoms. A single migration can mean a nonstop flight of up to 500 miles over a period of 18 to 22 hours and nectar such as they obtain from Cardinal Flower helps sustain them. This relationship is not one-sided however – it is mutually beneficial for both the bird and the plant. In acquiring nectar from the blossoms of Cardinal Flower, hummingbirds inadvertently perform a crucial task, that of pollinating many of the flowers they visit.
The blossoms of Cardinal Flower have two phases. In one the male reproductive part of the flower (the white “moustache” you see above the petals) matures and produces pollen. After the male structure matures and disappears, the female reproductive part develops and extends out from the same place where the male flower was. The flower parts mature at different times in different flowers on a given stalk, so both male and female flowers are present on the same plant at the same time. In order to reach the nectar from Cardinal Flower, a hummingbird must get into a position where the top of its head brushes against the flower’s reproductive parts. If the flower is in the male phase the hummingbird’s head gets dusted with pollen (see inset). If the flower it visits is in the female phase, the pollen on its head (from previous visits to male flowers) is deposited on the stigma of a female flower, pollinating the flower.
Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.
Turtlehead (Chelone glabra) can be found growing along stream banks and wetlands throughout eastern North America. This plant gets its common name from the flower’s long arching upper lip, or hood, which overlaps the lower lip like a turtle’s beak.
The male parts of the flower mature before the female parts, and when pollen is being produced these lips are very hard to pry open. Pollinators are primarily bumble bees, which are some of the only insects that have the strength to open the flower. When the female pistil matures, the lips relax a bit, so entry is easier. However, access to the nectar at the base of the flower is restricted (by a sterile stamen) to long-tongued insects. Thus, it is specifically long-tongued bumble bees that are able to both enter the flower and to reach the nectar. (Photo: bumble bee collecting pollen (see filled baskets on hind legs) from Turtlehead) Thanks to Jody Crosby for photo op.
Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.
You can’t get much redder than the red of Cardinal Flowers. Their petals act as brilliant red flags beckoning Ruby-throated Hummingbirds, who favor red, to come drink their nectar (and at the same time, pollinate them). Because their chief pollinator has wings and the ability to hover as it drinks, Cardinal Flower has no need for a landing platform, which most insect-pollinated flowers have.
Cardinal Flower has both male and female flowers. Above the red petals is a red tube, at the tip of which the reproductive parts of the flower emerge. First to appear are the male flowers, displaying pollen-bearing stamens. After they die, sticky, Y-shaped pistils extend from the flower, ready to receive pollen. The female flowers thus follow the male flowers (protandry). These flowers mature from the bottom to the top of the spike and you often see both male and female flowers on the same plant (just barely discernible in pictured flower spike).
Male flowers produce more nectar than female flowers, and hummingbirds seem to know this, as they spend most of their time at the youngest, and therefore male, flowers on the top half of the flower spike.
Trailing Arbutus (Epigaea repens) is one of our earliest spring wildflowers. Sometime in April or May the creeping, leathery, evergreen leaves of this plant suddenly come alive with white or pink tubular flowers. While they are delightful to look at, their fragrance is what truly sets them apart from many other plants that flower this time of year.
Because there aren’t that many insects about this early, nor flowering plants, insect predators can have a challenging time finding prey. The pictured crab spider chose its perch wisely: bumble bees are the main pollinators of Trailing Arbutus, and queens are out scouting for food as they begin to establish their colonies.
Indian Cucumber Root, Medeola virginiana, lives up to its name, as its rhizomes have a mild cucumber taste. Equally as enticing are its flowers — delicate and oh so intricate.
This member of the Lily family has one whorl of leaves if it isn’t going to flower (too young or without enough energy to reproduce), and two if it is. If there are two whorls of leaves, look under the top whorl and you will find flowers unlike any other you have seen. The pale petals fold back and from the center emerge three long reddish styles and several purple stamens (reproductive parts). Occasionally the flowers are above the topmost leaves, but typically they are below.
The change in position that Indian Cucumber Root flowers undergo as they develop into fruit is as fascinating as their appearance. The pedicels, or stalks, of these flowers become more erect once the flowers have been pollinated and fertilized, to the point where the dark blue berries mature above the upper whorl of leaves. You can see both stages in this photograph (styles have yet to fall off the developing fruits).
Naturally Curious is supported by donations. If you choose to contribute, you may go to https://naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.
Getting inside the flower of Bottle Gentian or Closed Gentian (Gentiana clausa), one of our latest flowering plants, in order to collect nectar and pollen is a monumental task that few insects, other than fairly large species of bumble bees, attempt. The petals are closed so tightly it takes even bumblebees several seconds of pushing, shoving and cramming to push the petals aside and get through the miniscule opening at the top of the blossom.
Pollen is the primary bumblebee attractant, as the sugar concentration of Bottle Gentian’s nectar is fairly low. Some bumble bees take a short cut – they chew a hole to gain access to the reproductive parts of the flower. The hole is often two-thirds of the way up the blossom, directly opposite the pollen-laden anthers within the flower. Look closely at the hole in the lefthand blossom in the photograph and the adjacent, dissected blossom, and you will see that the bee’s aim was dead on. You can even detect a portion of the anther through the hole.
If you examine plants that are still flowering this late in the season (such as asters, goldenrod and late-blooming turtlehead) early in the morning when it’s still quite cool or late in the day, many of the pollinators you see will be bumblebees, not honey bees. One reason for this is that they have different temperature tolerances for flight. You rarely see a honey bee when the temperature is below 57°F as they cannot fly when it is this cool. Bumblebees, however, are capable of flight when the air temperature is as low as 50°F.
Even so, bumblebees cannot take off unless their flight muscles are above 86°F; they maintain the temperature of their thorax (where wings and wing muscles are located) between 86°F and 104°F regardless of the ambient temperature. The way in which they raise the temperature of their thorax involves uncoupling their wing muscles so that the wings themselves do not move. They then use their wing muscles to shiver and raise the temperature of their thorax until it’s sufficiently warm enough for them to fly.
At rest a bumblebee’s body temperature will fall to that of its surroundings. If it is cool out, and the bumblebee wants to take flight, you can actually see its abdomen pumping to ventilate the flight muscles. An entomologist studying this phenomenon discovered that the rate of pumping can give an indication of the temperature of the bee. It ranges from around 1 pump per second when the bee is 86°F, to 6 pumps per second when it reaches 95°F.
The Pruinose Squash Bee (Peponapis pruinosa) is most often noticed when it’s gathering nectar or pollen from squash, pumpkin, watermelon or gourd blossoms. (Squash bees have been shown to be excellent pollinators of zucchini and butternut squashes, among others. If numerous, they thoroughly pollinate all available flowers, rendering later visits of honeybees superfluous. Before Europeans brought honeybees to the New World, squash bees were busy aiding the adoption, domestication, spread, and production of squashes and gourds by indigenous peoples throughout the Americas.) The bee’s black and white striped abdomen is easy to recognize.
While female squash bees are busy foraging for pollen in the flowers of plants in the Cucurbitae family, male squash bees can be seen darting between flowers, searching for mates. By noon, they are fast asleep in the withered flowers.
Pruinose Squash Bees are solitary bees, with every female digging her own nest in the ground. These consist of vertical tunnels that end with a number of individual chambers that are a foot or two deep in the soil. Each chamber is provided with an egg and a lump of pollen so that when the egg hatches, food is readily available. (Photo: five Pruinose Squash Bees packed into a single Bindweed flower)
At this time of year moist, rich woods are brilliantly lit up with the white flowers of a scraggly shrub called Hobblebush, whose name is derived from the tendency of its sprawling branches to trip people walking through the woods.
Hobblebush’s inflorescences consist of clusters of blossoms that together can measure six to eight inches across. The smaller flowers in the center (still buds in this photo) are fertile, possessing both stamens and pistils, while the larger flowers in the outermost ring are sterile. The inner fertile flowers produce fruit if pollinated and fertilized. The larger outer flowers, being sterile, do not produce fruit — their sole function is to attract insects to pollinate the central mass of fertile flowers.
Blue Cohosh, one of our early spring wildflowers, has diminutive flowers that open before its leaves fully expand. Like Wild Ginger, Blue Cohosh flowers are the color of rotting meat, which may account for the fact that flies are its main insect visitors. Flies tend to feed at a single flower until satiated, which is not conducive to cross-pollination, and thus most fertilization in Blue Cohosh is the result of self-pollination.
Native Americans treated a wide range of afflictions with Blue Cohosh, including gallstones, fevers, toothaches and rheumatism. The most common use of its rhizomes, or underground stems, was as an aid to speed and ease childbirth. Even today it still serves this purpose — 64% of midwives surveyed reported using Blue Cohosh to treat women before or during childbirth. It has, however, had deleterious effects on some women and has not been evaluated by the FDA.
If your home, shed or barn has weathered, unpainted wood and is riddled with ½”-diameter, perfectly round holes, there is a chance that carpenter bees are hibernating in them. Carpenter bees resemble bumblebees in both size and appearance (a carpenter bee has very few hairs on the top of its abdomen, which appears black and shiny, whereas bumble bee abdomens are often yellow and hairy), but they are not social insects. Instead of having a common nest in which they live and raise their young, carpenter bees drill holes in wooden structures or trees inside of which they chew tunnels that contain six to eight brood chambers for their young. After creating the chambers, the female carpenter bee places a portion of “bee bread” (a mixture of pollen and regurgitated nectar) in each one. On top of each pile of food she lays an egg and then seals off the chamber. The larvae eat and grow, pupate and emerge as adult bees in late summer. At this point they feed on nectar, pollinating a wide variety of flowers before they return to their tunnels to over-winter.
Having known since childhood that most insects have only one pair of antennae, imagine my surprise when I came upon a hornet on Queen Anne’s Lace that appeared to have two: a pair of slender, black antennae, and between them, a shorter pair of white ones. A bit of research revealed to me that in fact, these white “antennae” were actually the pollen sacs (pollinia) of an introduced and somewhat invasive orchid, Broad-leaved Helleborine (Epipactis helleborine).
Broad-leaved Helleborine is entirely dependent on insects to spread its pollen, especially wasps. It attracts them with nectar, which is said to have an alcoholic and narcotic effect which may help with the spreading of pollen, as an inebriated wasp is less likely to clean pollen off its body before leaving. Helleborine also produces a chemical which other plants produce and use to signal that they are being attacked by insects. It is used purely as a ruse by Helleborine, in order to attract wasps, Helleborine’s primary pollinators, who arrive to fend off other insects, and end up inadvertently collecting Helleborine’s pollinia.
Unlike the pollen of most plants, Helleborine’s pollen grains are so sticky that they cannot separate – thus, the entire package of pollen remains intact and is removed at one time. Wasps are capable of reaching the plant’s nectar without disturbing the pollinia, but cannot crawl out of the flower without striking against and detaching them and in so doing, getting them stuck to their heads. Can you find the pollinia in the insert photograph of a Broad-leaved Helleborine flower (which has not been visited by a wasp yet)?
Due to computer issues, Naturally Curious will resume posts next Tuesday, August 16.
Butterflies pollinate during the day while most flowers are open and they have better color perception than bees or even humans, but they are less efficient than bees at moving pollen between plants. Their legs and proboscis are longer and farther away from the flower’s pollen so they do not pick up as much pollen on their bodies. They also lack specialized structures for collecting pollen. Nevertheless, it is hard to imagine that some of the Daylily pollen that has collected on this Eastern Tiger Swallowtail’s wings might not fall onto or be brushed against the stigma of the next Daylily it visits.
Large-flowered Trillium (Trillium grandiflorum), also known as White Wake-Robin, is our largest and showiest species of trillium. It can be found throughout New England’s rich woods, sometimes carpeting large expanses of the forest floor in May and June. All species of trillium, as their name implies, have parts arranged in threes, or in multiples of three (petals, bracts, leaves, stamens, carpels).
Nectar, not fragrance, attracts long-tongued bumblebees to Large-flowered Trillium’s funnel-shaped blossoms. Self-pollination occasionally occurs, aided by the fact that as the flowers age, their stigmas reflex downward and come in contact with the anthers. The flowers are exceptionally long-lived, remaining open and fertile for two to three weeks.
When they first open, Large-flowered Trillium’s petals are white. As the flowers age, they become pale to deep pink (see insert). (There is also a pink form of Large-flowered Trillium which is pink from the time of opening.) The seeds that form are dispersed primarily by ants, but yellow jackets, harvestmen and white-tailed deer also contribute to their dispersal. It takes two years for the seeds to germinate and once established, Large-flowered Trillium plants typically require seven to ten years in optimal conditions to reach flowering size.
Miterwort (Mitella diphylla), also called Bishop’s Cap, is named for the resemblance of its two-peaked fruits to the hats (known as miters) worn by bishops of the Roman Catholic Church. This spring wildflower produces miniature five-pointed snowflake flowers that beg to be examined with a hand lens.
Gnats, small bees and syrphid flies all seek out Miterwort for its nectar. Because its nectaries are located just below the stamens, the flower is pollinated by the mouthparts of the pollinators which brush against the stamens when collecting nectar and the inadvertently-gathered pollen is transported to other Miterworts. Predators such as the Goldenrod Crab Spider (pictured) know that potential meals are plentiful near these delicate flowers.
Flowers that have limited opportunity to attract pollinating insects, such as those that mature very early in the spring, often are self-fertile – they can produce seeds without the benefit of pollinators. Wild Ginger (Asarum canadense) is a perfect example of this.
Wild Ginger has six inner stamens and six outer stamens, all of which produce pollen. In a newly-opened flower, all of these stamens lie flat against the “floor” of the flower. When the stamens are in this position, pollination is achieved by insects (often flies or beetles attracted to its rotten meat coloring and scent) as the pollen cannot reach the receptive stigma on its own. Wild Ginger hedges its bets, however. Whether or not pollination occurs early in its development, later in the life of the flower both inner and outer stamens move into an upright position, thereby moving closer to the stigma. Because the flower is oriented downward, this change in the position of the stamens allows for the pollen to fall onto the stigma, thereby accomplishing self-pollination. With or without pollinators, Wild Ginger succeeds in producing seeds.
Paper birch (Betula papyrifera) produces separate male and female flowers on the same tree, both in the form of catkins (cylindrical clusters of flowers). The catkins form in the fall and overwinter in a dormant state. In the spring they mature as the leaves develop, becoming pendulous. Male catkins are 2-4 inches long, whereas female catkins are usually 1 – 2 inches long. Both lack petals, enhancing wind pollination. After fertilization occurs, the male catkins wither away, while the female catkins droop downward and become cone-like.
The female catkins consist of tiny winged nutlets that are located behind three-lobed, hardened, modified leaves called bracts (yesterday’s blog post) and are usually dispersed by the wind during the fall and early winter. Birch bracts are species-specific — different species of birch have different-shaped bracts, allowing one to identify the species of birch that a bract comes from.
With frost just a whisper away, and in some areas not even that, there are still hardy plants, many in the Composite family (goldenrods, asters, thistles, Queen Anne’s Lace, Yarrow), which defy the odds and optimistically send forth blossoms on the off chance that there are still pollinators on the wing. Fortunately for them, bumblebees can and do fly at much cooler temperatures than honeybees and other pollinators. When food is plentiful and outside temperatures fall below 50°F., bumblebees generally stay inside their nest and live off their stores. At times when food is scarce or stores are low, they will forage when the outside temperature is as low as 43°F. (In severe conditions they have even been known to vary their flying height to and from the nest to take advantage of any temperature differences.) Locally, Tri-colored Bumblebees (Bombus ternarius) have a near monopoly on the last vestiges of nectar and pollen (see photo).
The flower of Red Trillium (Trillium erectum), also known as Stinking Benjamin and Wake Robin, is familiar to many, as it is one of our more common spring ephemerals. The three reddish-maroon (some populations have white, yellow-green, or paler red) petals of its flower are colored and smell faintly like rotten meat. Lacking nectar, these flowers rely on deception to bring in pollinators which are primarily flies and beetles that are typically attracted to dead animals.
Once a Red Trillium flower is pollinated, the Hershey Kiss-shaped red fruit begins to develop. The seeds of Red Trillium have oily appendages called “elaiosomes” which attract a number of insects, particularly ants. These elaiosomes (also called “ant snacks”) contain lipids and protein highly sought after by ants. The ants carry the seeds down into their underground tunnels where they feed the elaiosomes to their larvae and dispose of the seeds in their compost pile. Here they they put their droppings, or frass, as well as dead ants. Conditions for germination are ideal in such a spot, and, in fact, research shows a greater germination rate for seeds with elaiosomes than those without them.
Turtlehead, Chelone glabra, a member of the Plantain family (Plantaginaceae), can be found growing along stream banks and wetlands throughout eastern North America. Its long arching upper lip, or hood, overlaps the lower lip like a turtle’s beak, giving Turtlehead its common name. The male parts of the flower mature before the female parts, and when pollen is being produced these lips are very hard to pry open. Pollinators are primarily bumblebees, which are some of the only insects that have the strength to open the flower. When the female pistil matures, the lips relax a bit, so entry is easier, but access to the nectar at the base of the flower is restricted (by a sterile stamen) to long-tongued insects. Thus, it is specifically long-tongued bumblebees that are able to both enter the flower and to reach the nectar. If you look on the sides of the flowers, occasionally you will find where impatient bumblebees have chewed through to the nectar, avoiding the struggles involved in entering the flower in the traditional manner.
A walk in cool, moist woodlands this time of year may reward you with the sight (and smell) of One-flowered Wintergreen in bloom. The three- to six-inch-tall nodding flower has five waxy petals with rounded tips and wavy edges. Its true beauty can only be appreciated if you get down on your hands and knees and look underneath these petals. At this angle and close range, you not only can see the ten stamens and five-lobed stigma, but you can detect the flower’s delightful fragrance, which is very similar to that of Lily-of-the-Valley.
One-flowered Wintergreen’s blossom remains viable, without withering, for up to six weeks. After the flower is pollinated, the developing capsule becomes erect. Along with orchids, wintergreen seeds are the smallest in the plant kingdom – a single seed weighs around two-millionths of a gram. One-flowered Wintergreen is in the Heath family, which also includes rhododendrons, mountain laurel, azaleas, blueberries and cranberries.
A visit to a bog or marshy area at this time of year may well reward you with the sight of a striking orchid known as Calopogon or Grass-Pink (Calopogon tuberosus). Immediately noticeable are the fine, white “hairs” on the upper lip of the flower, which are thought to act as a “pseudopollen” lure, attracting native, recently-emerged bumblebees. The bees, expecting a reward of nectar and/or pollen, land on the hairs. At this point, the hinged labellum (part of flower that attracts insects and acts as a landing platform) swings down under the weight of the bee and positions the bee on the column (fused male and female structures located directly beneath the labellum), where pollen can be placed on its back. If the bee already carries a load of pollen, it will contact the stigma and thus pollinate the plant.
The month of June can’t go by without a mention of Showy Lady’s Slippers. Just fifty years ago, this orchid could be found over most of the Northeast. Habitat loss and an exploding deer population are considered major factors in Showy Lady’s Slipper’s decline, making it endangered or on the verge of extinction in many areas. Although rare, it is still locally abundant, particularly in fens (peat wetlands that get their water from rainfall and surface water).
As with Pink and Yellow Lady’s Slippers, one of Showy Lady’s Slipper’s three petals is greatly modified into a large inflated pouch called the labellum . (The pouch’s color can vary widely from year to year, depending on the ambient temperature. Cooler conditions appear to produce more intense color.) The petals on either side of the pouch attract pollinators with an alluring odor, but the insects that enter into the pouch are in for a disappointment, as lady’s slippers produce little or no nectar. The structure and positioning of the pistil and stamens are such that they encourage cross-pollination to take place, which is crucial, as lady’s slippers rarely self-pollinate.
The flowers of Pitcher Plants are just as unusual and fascinating as their insect-luring leaves. These plants can be found blossoming during a two to three week period in the spring (late May-June). Although the maroon petals hanging down typically prevent you from seeing the structure of the flower, it more or less resembles an upside-down umbrella. Within one to two days of the flower opening, the stigmas become receptive and the anthers shed their pollen, which falls into the umbrella-like tray where insects travel on their way to the stigmas. Ants are almost invariably present in the flowers, attracted by the abundant nectar, but they are probably of little importance as pollinators. Bees and flies appear to be the primary pollinators of Pitcher Plants.