Looking carefully at the evidence, there were at least five ‘fathers’ of Impressionism: Eugène Boudin, Johan Barthold Jongkind, Édouard Manet, Camille Corot, and Adolphe-Félix Cals (1810–1880). While most of those are already well known, Cals seems to have become forgotten through the twentieth century.

He initially trained as an engraver, then gained a place at the École des Beaux-Arts in Paris, where he entered the studio of Léon Cogniet (1794-1880), a history and portrait painter in Paris who was a prolific teacher. His paintings were first accepted for the Salon in 1835, and until 1870 he seldom missed a year, except in 1863 when his work was shown in the Salon des Refusés. In 1862, when Monet became very ill in Algiers, he provided support and helped him return to painting afterwards.

From 1871, he divided his time between Paris, and painting around Honfleur, where he developed his Impressionist style and met with Boudin, Jongkind, and the core Impressionists. Although one of the older artists in the group, he was very enthusiastic about the movement, and encouraged its younger members. He also showed works in the second, third and fourth Impressionist Exhibitions. His paintings were collected by his patron, Count Armand Doria of the Château d’Orrouy in Picardy, whom he visited, with Colin, Manet, and Corot.

Possibly his painting accepted for the Salon in that year, Peasant Woman and Child (1846) appears influenced by Millet, with its realistic depiction of rural squalor, and the telling wine bottle in the basket.

His Cliffs near Dieppe (1862) shows the radical change which early Impressionism brought, presumably with the influence of Boudin, Jongkind, and Monet.

Two Friends Around a Table (1864) is a wonderful chalk sketch which appears prescient of the much later drawings of Seurat, with atmospheric highlights added.

One of a pair of paintings of the same location, The Well in Rue Montlaville, Orrouy, Viewed from the East (1866) is a plein air oil sketch showing the influence of Corot. Count Doria, his patron, had his estate here, at Orrouy, to the north of Paris.

According to the catalogue, Cals showed six paintings at the First Impressionist Exhibition in April 1874, identified as:

• Portrait of Madame Ed. G,
• The Good Father Fisherman at Honfleur,
• Old Fisherman,
• Landscape,
• Happy Woman Knitting,
• Spinner.

His Fisherman (1874) was almost certainly shown at the First Impressionist Exhibition, and appears to be a view of sea cliffs on the north French coast near Honfleur.

His undated Landscape with a Farmyard was probably painted at or near Saint-Siméon, the farm near Honfleur which became the focus of several Impressionist painters, and the subject of many of Cals’ paintings after 1871.

In Saint-Siméon or The Big Farm at Honfleur (1876), he shows an empty easel set up in the orchard at the farm, with several figures scattered around. His plainly visible brushstrokes appear to be organising themselves, much as Vincent van Gogh’s did nearly twenty years later.

A Sunday in Saint-Siméon (1876) shows another view of Saint-Siméon’s orchards.

Honfleur Alley (1877) also has passages rich with swirling brushstrokes, but sacrifices none of its details for its painterliness.

In his Sailors in Saint-Siméon (1877) the fruit trees show the influence of Corot.

After the Fourth Impressionist Exhibition in 1879, when he was in his late sixties, his health deteriorated, and he died the following year in Honfleur. It has been claimed that some of his paintings were exhibited at the Sixth Impressionist Exhibition in 1881, in his honour. His work was still sufficiently popular in 1900 for Georges Petit Galleries to publish his biography by Arsène Alexandre, which is freely available at Archive.org.

References:

Hans Weevers’ page with a thorough literature survey.
The First Impressionist Exhibition (in Italian), containing
the exhibition catalogue