Question: What kind of flowers did Van Gogh paint?
About the article "Sunflowers (Van Gogh series)", section "Sunflowers, friendship and gratitude".

Candidate passages:
In Paris Van Gogh learned to paint more than what one sees, but what is should be.
Van Gogh felt "Pink Orchard" was an example of wise use of that technique, such as leaving a field blank behind the orchard to create the feeling of distance.
The way in which he outlined the bark of the tree indicates influence of the Japanese prints that he greatly admired.
Using an Impressionist technique of placing colors side by side, Van Gogh makes short dots or brush strokes of colors to represent grass.
On the top of the tree he uses rougher, more impasto brushstrokes to represent the colorful blossoms.
Van Gogh asked his brother Theo to "shave off" some of the impasto in this painting.
Apparently he did not reline, a process of heavy pressure and heat to flatten the surface, because the paintings sharp edges of thick impasto remain. 
"Vase with Zinnias and Geraniums" (F241) reflects the influence of Adolphe Monticelli (1824–1886) in its vivid color and impasto paint.
Van Gogh admired, and later collected, Monticelli's work.
Van Gogh had been introduced by his brother Theo to Monticelli's still life work with flowers in Paris.
He admired Monticelli's use of color as an expansion of Delacroix's theories of color and contrast.
Secondly he admired the effect Monticelli created by heavy application of paint called "impasto".
It was partially Monticelli, from Marseilles, who inspired Van Gogh's southerly move to Provence in 1888.
He felt such kinship for the man, and desire to emulate his style, that he wrote in a letter to his sister Wil that he felt as if he were "Monticelli's son or his brother."
The first owner in the provenance of this painting is "C.M.
van Gogh Gallery, Amsterdam, The Netherlands", which was owned by Van Gogh's uncle and an art dealer, Cornelius Marinus van Gogh (1824–1908).
"Bowl with Zinnias and Other Flowers" (F251), painted within days of "Vase with Zinnias and Geraniums" (F241), is evidence of Van Gogh's transition to a lighter color palette.
Picking up elements of Impressionism Van Gogh painted with a more vigorous brushstroke, with thick application of paint, called "impasto" which created a three-dimensional relief.< 
Van Gogh's paintings of rose, or any flowers, are evocative of his quote, "Ah, what portraits could be made from nature with photography and painting."
Portrait of Artist's Mother is a painting Vincent van Gogh made in 1888 of his mother, Anna Carbentus van Gogh from a black-and-white photograph.
In September 1888 Van Gogh - answering to a letter of his sister Wil who had told him of a recent photograph of their mother - asked for a print.
About a week later he received it, but - ""troubled by the black"" - sat down to paint a copy based on this likeness: Van Gogh's initial introduction to art was through his mother, an amateur artist.
After years of strained relationship with family members, Van Gogh excitedly shared some of his works his mother would cherish most, those of flowers and natural settings.
In this painting of his mother, Van Gogh captures her dignified, proud nature.
Van Gogh made the painting, " Memory of the Garden at Etten", to depict an older woman who he envisioned as his mother and a younger woman in a plaid shawl to represent his sister Wil and the lovely gardens of the Netherlands.
In a letter to his sister Wil Van Gogh said he had "an impression of you like those in Dicken's novels."
Van Gogh went to Arles for the sun, color and country lifestyle but more than anything else "what I really hope to do is paint a good portrait."