HAVANA – When Fidel Castro suddenly decided to shed his trademark olive green military fatigues and don street clothes in public for the first time in 35 years, a white guayabera shirt over blue slacks is what he put on.

A resolution from the Foreign Relations Ministry published into law Wednesday makes the guayabera Cuba’s official formal dress garment and mandates that government officials wear them at state functions. That’s welcome news in a country known for its steamy summer weather.

The law confirms the decades-old reputation of the cool, roomy cotton or linen shirts – with four large pockets and pleats down the front, traditionally worn untucked – as the island’s most quintessential fashion choice.

“The guayabera has been a part of the history of our country for a long time and constitutes one of the most authentic and legitimate expressions of Cubanism,” the resolution said.

According to the law, male officials are to wear white, long-sleeved guayaberas at state events; women can vary color and style.

Nearly all Cuban officials already shun suits and sport jackets in the tropical heat, so the law isn’t likely to change much.

The guayabera also is a fashion fixture in Mexico, parts of Florida and even as far away as the Philippines. It is said to have originated in Cuba, though no one is sure exactly where or when.

The resolution offered no definitive answer as to the shirts’ origin, but gave the tradition a political and socio-economic spin: Guayaberas “have been worn with pride and satisfaction” by Cubans of all backgrounds, it said, “evolving from their rural roots to reach various sectors of the urban population.”

In Castro’s case, his wardrobe shift came during a 1994 summit in Colombia, and only then at the urging of his friend, Nobel Prize-winning author Gabriel Garcia Marquez.

After a health crisis forced him to cede Cuba’s presidency to his younger brother Raul in July 2006, Fidel Castro took to wearing 1970s-style track suits, short-sleeve dress shirts and other attire – though he now sometimes appears in fatigues devoid of any rank or insignia.

Raul Castro dons guayaberas for many public occasions, including sessions of parliament and meetings with visiting foreign dignitaries.

In 2007, Cuba opened a guayabera museum in the city of Sancti Spiritus, capital of the province of the same name, and the shirt has symbolic value predating the revolution that swept the Castro brothers and their bearded band of rebels to power on New Year’s Day 1959.