Hulot and Flessel were among the most popular ministers in the government and their successors will have trouble matching their public profiles.
Hulot's departure, complaining that he felt "isolated" in the cabinet in defending the ecology, was a serious blow to the government, and has done nothing to stop President Emmanuel Macron and Prime Minister Edouard Philippe's fall in the opinion polls.
De Rugy, 44, does have green credentials, however.
He was a member of the Green Party and its successor, EELV, for 20 years before leaving the party in 2015, accusing his comrades of "ultra-left excesses".
He and another ex-Green Barbara Pompoli are the only MPs in Macron's Republic on the Move with a substantial background in environmental campaigning.
Considering himself a "reformist ecologist", he is seen as more dependable than his predecessor, if less glamorous.
"We couldn't go through what we went through with Hulot again, someone uncontrollable who can storm out after three months," an insider told Le Monde newspaper.
Although he said he was not a candidate for a new job when the Hulot crisis broke, de Rugy has dropped heavy hints on Facebook in the last few days.
The job, officially regarded as the third most important in the government, is "one of the most difficult", he said on 28 August, continuing "You have to show determination, commitment and perseverance over time."
The post went on to make a declaration of pragmatism that could have been specifically designed to please the president.
"Ecology can't just be big analytical speeches, denunciations or even proposals but action, more action and always action."
He clearly intends to stay.
"Whoever succeeds to this difficult responsibility must have the time to do the job," he declared after Hulot's resignation.
Nevertheless, he may not have been the first choice.
At the weekend Macron phoned MEP and former student rebel Daniel Cohn-Bendit, who said they finally agreed it would not be a good idea for him to take the job.
And Pascal Canfin, a former development minister who now heads WWF France, announced on Tuesday he was not taking it, either.
Swimmer takes on sports ministry
In replacing Flessel, Maracineanu has a less intimidating challenge before her, even if her ministry must prepare for the 2024 Paris Olympics.
Born on 7 May 1975 in Romania won a silver medal in backstroke at the 2000 Summer Olympics in Sydney and was world champion in 1998.
In July Prime Minister Edouard Philippe gave her the task of reducing the number of people who drown off the French coast.
The Mediapart website on Tuesday afternoon claimed that Flessel resigned because the tax authorities were looking into possible fraud accusations relating to tax declarations for a company she was associated with.
An announcement on another challenge facing the government - whether to postpone the changeover to PAYE taxation from the planned date in January - is expected later in the day.