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Pollination

Large-flowered Trillium Flowering

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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.

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Miterwort Flowering

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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.

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Wild Ginger Hedges Its Bets When It Comes To Pollination

5-2-16  wild ginger 020Flowers 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.

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Paper Birch Catkins: Winged Nutlets & Bracts Dispersing

12-8-15 white birch female catkin 005Paper 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.

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Bumblebees Foraging Fall Flowers

10-5-15 tri-colored bumblebee IMG_1479With 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).

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Red Trillium Seeds Being Dispersed By Ants

9-10-15 red trillium fruit and seeds  092The 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.

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Turtlehead Flowering & Being Pollinated By Bumblebees

8-14 turtlehead 073Turtlehead, 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.

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