León Tolstoi (graf). Los Cosacos. Andres Bello, 19??, p. 103–. GGKEY:X9EAG7TJAD6.
indiana.edu
plantsinmotion.bio.indiana.edu
Hangarter, Roger P. «Solar tracking: sunflower plants» (en anglès). Plants-In-Motion website. Indiana University. [Consulta: 22 agost 2012]. «Many people are under the misconception that the flower heads of the cultivated sunflower (Helianthus annuus) track the sun... Immature sunflower flower heads do exhibit solar tracking and on sunny days the buds will track the sun across the sky from east to west... However, as the flower bud matures and blossoms, the stem stiffens and the flower head becomes fixed facing the eastward direction.»
kew.org
powo.science.kew.org
«Helianthus annuus» (en anglès). Plants of the World Online. Royal Botanic Gardens. Kew. [Consulta: 20 octubre 2023].
