In “Melon Field,” the most recent piece in the Smithsonian American Art Museum’s exhibit of paintings by Texas-born artist John Alexander, a black bird pokes around the remains of a field full of crushed and broken watermelons.

Alexander saw a lot of watermelon fields growing up in Texas, but this painting has a larger significance to him. “You take something beautiful, like a watermelon. For something so simple and wonderful to be desecrated in a violent way, it gets at the goriness and bloodiness of conflict,” Alexander said in an interview Wednesday.

“John Alexander: A Retrospective,” which opens today at the Smithsonian Institution’s American Art Museum, takes the viewer on a tour of Alexander’s 30-year career. The paintings are arranged topically, instead of chronologically, said museum Chief Curator Eleanor Harvey, with special attention to how they “play off one another.”

Harvey said her “driving motivation was to let John, through the paintings, put his best foot forward” and to maintain a good balance of his earlier and more recent work. The artist completed “Melon Field” just weeks ago.

Alexander’s work includes many realistic charcoal and watercolor pictures of fish and birds, pieces he said are the result of a decision several years ago to “learn his craft better.” He had delivered a speech to graduates at the Rhode Island School of Design and, looking over the sea of young people about to enter the art world, he asked himself, “What are you going to do now?”

“I don’t want to be like some other artists repeating themselves endlessly,” he said. So he bought flowers and fish from the market, grew plants in his garden, and went into nature with the purpose of “really working from observation. … I wasn’t trying to create great art, but I tried to get better as a draftsman.”

The serenity of his nature imagery and studies of birds and fish contrasts with the violent chaos that characterize some of his earlier work — such as the massive “I’ve Been Living in a Hydrogen Bomb” — and the biting satire that re-emerges in his most recent paintings.

Throughout the 30-year span, the people in Alexander’s works frequently have been shown in masks with long, beaklike noses. The artist said this evolved from his paintings of birds. The masks keep the subjects anonymous, preserving the paintings’ universal applicability, he said. They also are a jab at human pomposity.

“I don’t try to paint people in the most flattering way, and when you put a mask on them, they look even more ridiculous,” he said. “An L.A. daily once wrote about me that I paint nature at its best and human beings at their worst — I really like that line.”

Viewers looking for political satire may be particularly drawn to “Ship of Fools,” where men in suits, bound with ropes and chains, look around nervously as their tiny rowboat sinks into a river. A skeleton mans the paddle, and two more float in the river. One of the men aboard holds a golden crucifix spurting blood.

“I always thought the ship could be interpreted as the ship of state, or something even bigger,” Alexander said. “Here’s a rowboat, totally overcrowded, the people on it are not dressed appropriately, the captain does not know where he’s going and has a monkey on his back. That pretty well sums up my feelings about the most recent period we’ve gone through.”

The artist’s own favorite — the painting he says “gave me chills when I looked at it, I was so proud of it” — mixes lush natural realism with a self-described apocalyptic view of the future. In “Glory Bound,” a locomotive emerges from a tunnel into a dense jungle. It’s a commentary, Alexander said, on nature’s losing battle against commerce.

“The birds are looking at this mechanical monster coming out of this dark hole; it’s the beginning of the end for them,” he said.

Alexander painted “Glory Bound” after spending some time in South America, and it captures his fear about the decline of forests and jungles as humanity continues to expand its reach.

“Starbucks has done really well; the trees and birds aren’t doing as well,” he said. “Nothing against Starbucks.”

“John Alexander: A Retrospective” opens today and will remain on display through March 16. The museum will host a gala with the artist on Jan. 24. The Donald W. Reynolds Center for American Art and Portraiture is located at Eighth and F streets Northwest, above the Gallery Place/Chinatown Metro station. It is open 11:30 a.m. to 7 p.m. daily, except on Christmas Day.