Why do flowers of Tristerix corymbosus (Loranthaceae) ?face down??

TADEY, M. ; AIZEN, M.A.

FUNCTIONAL ECOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2001 vol. 15 p. 782 - 790

0269-8463

1.Pendant flowers are common among hummingbird-pollinated plants. A downwardorientation of the flower or inflorescence could represent an adaptation to avoid eitherflower flooding or direct pollen losses from anthers or stigmas under rainy conditions.2.We studied the adaptive significance of this trait experimentally inTristerix corymbosusKuijt (Loranthaceae), a mistletoe native to the temperate forests of southern SouthAmerica. We applied three treatments: (i) natural pendant inflorescences; (ii) inflorescencestethered to face up; and (iii) inflorescences tethered to face down (as a controlfor tethering). We also considered natural exposure to rain as a second factor.3.The treatments did not differ significantly in either nectar volume or concentration.Flowers exposed to rain for most of their lives contained more diluted nectar thanthose that remained dry, but this result did not depend on either inflorescence or flowerorientation.4.We found significantly fewer pollen tubes in styles of flowers from inflorescencestethered to face up than in flowers receiving the other two treatments, but this couldnot be attributed to a direct effect of rain exposure. Inflorescence orientation did notaffect either the number of pollen grains left in anthers or seed set. No strong evidencewas found for differential visitation by hummingbirds in relation to a flower?s angle.5.The results of this work support neither the flower-flooding nor the pollen-protectionhypothesis. However, a flower?s orientation may affect the extent of within-flower selfpollinationor the efficiency of pollen transfer from a hummingbird?s bill onto a flower?sstigma.