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Archive for August 10, 2020

Ruby-throated Hummingbirds Pollinating Cardinal Flower

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.

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