14.1: Pollination Syndromes

Flowers have coevolved with their pollinators. The shape, color, smell, and many other features of a floral phenotype are adapted to their method of pollen dispersal. This set of characteristics is called a pollination syndrome and allows scientists to make inferences about the pollinator of a particular flower. Some of these are more obvious, while others, more cryptic. For example, humans do not see ultraviolet (UV) light, but many insects can (like bees). Flowers might be communicating with UV light in a way that might not be apparent to humans until you shine a UV light on them. In the Malva assurgentiflora flower (Figure \(\PageIndex{1}\)), the pollen has UV fluorescence.

Figure \(\PageIndex{1}\): A Malva assurgentiflora flower in regular light (first photo) and ultraviolet light (second photo). In the first photo, the pollen looks a dull white and the petals are a vibrant fuschia pink. In the second photo, the petals appear dark burgundy purple, while the pollen is a glowing neon blue. The pollen of this flower has UV fluorescence; when the pollen absorbs UV light, it emits it at a different frequency and appears to glow. Photos by Alan Rockefeller, CC-BY-SA.

Pollination Syndromes and Vectors

Though flower phenotypes can also correlate to other environmental factors (e.g. Peach et al. 2020), we can connect pollination syndromes to pollen vectors, both biotic and abiotic (see Table \(\PageIndex{1}\)).

Table \(\PageIndex{1}\): Pollination Syndromes (adapted from the US Forest Service).

Pollination Syndrome	Color	Structure	Scent	Nectar or Pollen
Wind	Dull, perianth often absent or reduced	Large feathery stigmas, large anthers	None	No nectar, large amounts of pollen
Birds	Reds and pinks	Often tubular or cupped	None	Lots of hidden nectar, moderate pollen
Bees	Purples, blues, yellows, white, UV	Flat and shallow or tubular, with landing area	Sweet, fresh, mild	Pollen often sticky and scented, nectar usually present
Bats	White, dull green, or purple	Often bowl-shaped or pendant, anthers protruding	Musty or fruity, strong, emitted at night	Lots of hidden nectar
Moths	White, pale pink or purple	Often tubular or cupped, no landing pad	Strong and sweet, emitted at night	Lots of hidden nectar, limited pollen
Butterflies	Bright colors	Tubular, with wide landing pad	Faint, fresh	Lots of hidden nectar, limited pollen
Flies	Dark red, purple, brown	Shallow, funnel, or trap-like	Putrid, rotting	No nectar, moderate pollen

Figure \(\PageIndex{2}\): Trillium ovatum flowers are white until they have been pollinated, at which point they begin to turn pinkish-purple. In the image above, the flower on the left has been pollinated, while the one on the right has not. Photo by Maria Morrow, CC-BY 4.0.

Examples of Pollination Syndrome Characteristics

Bees, Bee-Like Flies, and Butterflies

Figure \(\PageIndex{3}\): The yellow color and surface for an insect to land and crawl around on in this head inflorescence are characteristic of bee pollination. However, this flower does not smell particularly fresh or sweet. Instead, the odor is more astringent and a bit unpleasant. Photo by Maria Morrow, CC-BY 4.0.

Figure \(\PageIndex{4}\): These foxglove florets are purple and bell-shaped. The lower petal serves as a landing pad for bees, with a speckled pathway (nectar guide) to lead the bee to the nectar at the center of the flower. The anthers are visible on the lowest full floret, dangling above the entrance to deposit pollen on the bee's back as it crawls in. Photo by Maria Morrow, CC-BY 4.0.

Figure \(\PageIndex{5}\): This Iris flower has a bee pollination syndrome. The primary colors are purple and yellow. There are nectar guides leading the bee to the center of the flower. To get there, the bee must crawl under the stigma first, then under the anthers. This flower has a pleasant, sweet smell. Photo by Maria Morrow, CC-BY 4.0.

Figure \(\PageIndex{6}\): This Delphinium flower has a butterfly pollination syndrome (this also works for long-tongued bees). The color is purple, there is a lipped petal that serves as a landing pad, and there is a long nectar spur extending from the back of the flower. This flower has a pleasant, sweet smell. Photo by Maria Morrow, CC-BY 4.0.

Birds

Figure \(\PageIndex{7}\): These flowers have a bird pollination syndrome. The Fuschia (left) is pink and purple, pendant, and relatively odorless. The nectar is located deep within the flower at the base of a hypanthium. The Castilleja (right) is bright red with many tubular flowers (these could also be butterfly pollinated). First image by Peter Clarke, CC BY-SA 3.0 via Wikimedia Commons. Second image by Maria Morrow, CC-BY 4.0.

Figure \(\PageIndex{8}\): A hummingbird pollinating red, tubular flowers. The anthers and stigma extend below where the hummingbird enters, rubbing it on the chin and chest when it goes in for nectar. Photo by VJAnderson, CC BY-SA 4.0 via Wikimedia Commons.

Flies and Beetles

Figure \(\PageIndex{9}\): Fritillaria flowers are often fly pollinated. The dark red splotches on the petals and overall unpleasant smell fit a fly pollination syndrome. Check out this page to see Fritillaria species being pollinated by flies. Photo by Maria Morrow, CC-BY 4.0.

Figure \(\PageIndex{10}\): These flowers have a beetle pollination syndrome. Beetles prefer white to green flowers with a large place to land. First image from Pollinator at the English language Wikipedia, CC BY-SA 3.0 via Wikimedia Commons. Second image by Sweetbay_Magnolia_Magnolia_virginiana_Flower_Closeup_2242px.jpg: Photo by and (c)2008 Derek Ramsey (Ram-Man). Co-attribution must be given to the Chanticleer Garden.derivative work: Bff, CC BY-SA 3.0 via Wikimedia Commons.

Wind

Figure \(\PageIndex{11}\): Wind pollinated flowers have a reduced or absent perianth, large anthers, and feathery stigmas. This grass spike has large pinkish anthers dangling from long filaments. Feathery stigmas can be seen emerging from some of the florets. Photo by Maria Morrow, CC-BY 4.0.