nectar guide

File:Mimulus_nectar_guide_UV_VIS.jpg

Nectar guides are markings or patterns seen in flowers of some angiosperm species, that guide pollinators to their rewards. Rewards commonly take the form of nectar, pollen, or both, but various plants produce oil,{{cite journal |author=Buchmann, SL. |year=1987 |title=The ecology of oil flowers and their bees |journal=Annual Review of Ecology and Systematics |volume=18 |issue=1 |pages=343–70 |doi=10.1146/annurev.es.18.110187.002015}} resins,Reis Mariza G.; de Faria, Aparecida D.; Bittrich, Volker; do Carmo, Maria; Amaral E.; Marsaioli, Anita J. : The Chemistry of Flower Rewards : J. Braz. Chem. Soc., Vol. 11, No. 6, 600-608, 2000. scents,Teichert, Holger; Pollination biology of cantharophilous and melittophilous Annonaceae and Cyclanthaceae in French Guiana; Doctoral dissertation at University of Ulm, 2008 or waxes. Such patterns also are 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 & LunauDinkel T., Lunau K.: How drone flies (Eristalis tenax L., Syrphidae, Diptera) use floral guides to locate food sources. Journal of Insect Physiology Volume 47, Issue 10, September 2001, Pages 1111-1118). Pollinator visitation can select for various floral traits, including nectar guides through a process called pollinator-mediated selection.

These patterns are sometimes visible to humans; for instance, the Dalmatian toadflax (Linaria genistifolia) has yellow flowers with orange nectar guides.{{cite web | url = http://www.usgs.nau.edu/swepic/factsheets/lidasf_info.pdf | title = Dalmatian Toadflax (Internet Archive) |archiveurl = https://web.archive.org/web/20070317043446/http://www.usgs.nau.edu/swepic/factsheets/lidasf_info.pdf |archivedate = 2007-03-17}} However, in some plants, such as sunflowers, they are visible only when viewed in ultraviolet light. 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 pollinators such as honey bees and other insects that can see ultraviolet. [http://webexhibits.org/causesofcolor/17C.html This page] on butterflies shows an animated comparison of black-eyed Susan (Rudbeckia hirta) flowers in visible and UV light.{{Cn|date=February 2021}}

The ultraviolet color, invisible to humans, has been referred to as bee violet, and mixtures of greenish (yellow) wavelengths (roughly 540 nmBriscoe, Adriana D.; Chittka, Lars. The Evolution of Color Vision in Insects. Annu. Rev. Entomol. 2001. 46:471–510) with ultraviolet are called bee purple by analogy with purple in human vision.{{cite book | title = The Social Behavior of the Bees: A Comparative Study | author = Charles D. Michener | publisher = Harvard University Press | year = 1974 | isbn = 0-674-81175-5 | url = https://books.google.com/books?id=aordrL_D-30C&dq=%22bee+purple%22&pg=PA17 }}