Nectar guides are markings or patterns seen in

flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

s of some

angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit ...

species, that guide pollinators to their rewards. These markings may appear as lines, spots, or "blotches". Such patterns are also known as "pollen guides" and "honey guides", though some authorities argue for the abandonment of such terms in favour of ''floral guides'' (see, for example, Dinkel & Lunau).

Pollination

Nectar guides serve as an interspecific signal that the flower contains a reward. Rewards commonly take the form of

nectar Nectar is a viscous, sugar-rich liquid produced by Plant, plants in glands called nectaries, either within the flowers with which it attracts pollination, pollinating animals, or by extrafloral nectaries, which provide a nutrient source to an ...

pollen Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced Gametophyte#Heterospory, microgametophytes), which produce male gametes (sperm ...

, or both; however, plants may also produce oil, resins, scents, or waxes. Pollinator visitation can select for various floral traits, including nectar guides, through a process called pollinator-mediated selection. For example, nectar guides are thought to increase pollinator foraging efficiency by reducing handling time. These guides may also decrease

nectar robbing Nectar robbing is a foraging behavior used by some organisms that feed on floral nectar, carried out by feeding from holes bitten in flowers, rather than by entering through the flowers' natural openings. Nectar robbers usually feed in this way, ...

, which leads more pollen to be transferred and ultimately increases plant fitness.

Visibility

Nectar guides are sometimes visible to humans; for instance, the Dalmatian toadflax (''Linaria genistifolia'') has yellow flowers with orange nectar guides. However, in some plants, such as the meadow buttercup (pictured to the right), they are visible only when viewed in

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

light Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...

. Under ultraviolet, the flowers have a darker center, where the nectaries are located, and often specific patterns upon the petals as well. This is believed to make the flowers more attractive to

pollinator A pollinator is an animal that moves pollen from the male anther of a flower to the female carpel, stigma of a flower. This helps to bring about fertilization of the ovules in the flower by the male gametes from the pollen grains. Insects are ...

s such as

honey bee A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to mainland Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the ...

s and other

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s that can see ultraviolet light
This page
on butterflies shows an animated comparison of black-eyed Susan (''Rudbeckia hirta'') flowers in visible and UV light. The ultraviolet color, invisible to humans, has been referred to as ''bee violet'', and mixtures of greenish (

yellow Yellow is the color between green and orange on the spectrum of light. It is evoked by light with a dominant wavelength of roughly 575585 nm. It is a primary color in subtractive color systems, used in painting or color printing. In t ...

) wavelengths (roughly 540 nm) with ultraviolet are called ''bee purple'' by analogy with

purple Purple is a color similar in appearance to violet light. In the RYB color model historically used in the arts, purple is a secondary color created by combining red and blue pigments. In the CMYK color model used in modern printing, purple is ...

in human vision.

References

External links

Dalmatian Toadflax
from the Southwest Exotic Plant Information Clearinghouse.
(See archived version on th
Internet Archive
-- accessed on 2009-03-17).
UltravioletPhotography.com
Online library of ultraviolet floral signatures. {{botany-stub Pollination