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Pollen Dispersal

Broad-leaved Helleborine Dispersing Pollen

8-10-16  helleborine pollinia 021Having 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.

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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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Grass of Parnassus Flowering

e-grass of Parnassus 008Grass of Parnassus, Parnassia glauca, (also known as Bog- Star) was named after Mount Parnassus in central Greece. It is not a type of grass, but rather, belongs to the family Celastraceae and can be found growing in fens, bogs and swamps. The striking green lines on its petals guide flies, bees and other pollinating insects to the flower’s supply of nectar.

The structure of Grass of Parnassus’s flower is not typical. In between its five functioning stamens and five petals there is a whorl of five sterile stamens, each of which is three-pronged. The spherical tip of each prong mimics a glistening droplet of nectar. These stamens do not actually produce any nectar – they are there purely to attract pollinators. The actual nectar is located near the base of these false, or sterile, stamens. Only one of the five true stamens in the flower is active at any one time, with each producing pollen on average once every 24 hours.

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Goldenrod Crucial To Honeybee Survival

8-13  honeybee and goldenrod 028Goldenrod is one of the most important flowering plants for honeybees because it is a prolific producer of nectar and pollen late in the year. Blooming in the late summer and fall, this bright yellow-flowered composite provides nectar for the bees to build up stores of honey for winter. (Goldenrod honey is dark amber and strong tasting.) Goldenrod also provides pollen to help stimulate the colony to produce brood late into the fall. The pollen adds considerable amounts of protein, fats, and minerals to the diet of the late-season bees, helping ensure that they will have food throughout the winter.

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Pitcher Plants Flowering

6-5-15  pitcher plant 007The 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.

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Beaked Hazelnut Flowering

beaked hazelnut 400The blossoms of many shrubs are not necessarily big, flashy, strong-scented flowers, especially if they are wind-pollinated and have no need to attract insects. Beaked Hazelnut’s flowers are now blooming – pendant male catkins loaded with pollen and ¼ “- diameter female flowers. The female blossoms should be examined through a hand lens – they are exquisite little maroon flowers with magenta highlights and pistils that curl this way and that, in hopes of catching pollen grains. One advantage to flowering now, before leaves are out, is that the wind-dispersed pollen has fewer obstructions.

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Bloodroot Pollination

4-30-15  bloodroot 084Thank you for all your guesses, a vast majority of which were right on the mark. Bloodroot, Sanguinaria canadensis, is one of the first spring ephemerals to bloom. On sunny days its petals are open wide, closing at night when the temperature drops and on cloudy, rainy days (when pollinating insects are less apt to visit). Only pollen is produced by Bloodroot – no nectar. Even so, insects, especially mining bees, visit and collect pollen, and in the process often pollinate the flower.

The methods which Bloodroot employs in order to become pollinated are impressive, to say the least. While cross-pollination is preferable, self-pollination is better than nothing. To limit self-pollination, the female stigma becomes receptive before the male anthers of the same flower produce pollen. Furthermore, during the first few days of the flower opening, the anthers bend downward toward the outside of the flower, away from the receptive stigma, where they are easily accessible to insects. If insect pollination doesn’t take place by the third day of flowering, however, the anthers bend inward, contacting the stigma and self-pollinating the flower.

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