A FLUSH of green is spreading across the Arab world, but not because its vast deserts are shrinking. Green is the colour of Islam and Islamist movements have reaped the biggest harvest of the Arab spring. Not all stripes of Koran-led politics have flourished equally. In the Sunni Muslim heartlands stretching from the Atlantic to the Persian Gulf, neither violent extremists in the mould of al-Qaeda, nor proponents of Iranian-style theocracy, nor woolly Islamist liberals have fared especially well. Instead, the prize is going to groups linked to the centrist Muslim Brotherhood, committed to evolutionary rather than revolutionary change, and more concerned with questions of Islamic identity and ethics than with imposing rigid God-given rules.

Parties aligned to the Brotherhood now dominate politics in both Egypt and Tunisia, having captured nearly half of parliamentary seats in post-revolutionary elections. Seeking to avoid the fate of those countries' fallen presidents, King Muhammad VI of Morocco has empowered his own country's Brothers by appointing the head of their Justice and Development Party as prime minister. Islamist militias were among the most effective in Libya's revolutionary war. Like-minded armed groups look set to play a similar role in Syria as it slides towards civil war.

The Brothers, known to Arabs as the Ikhwan, are hardly newcomers to the political scene. Their political arm in Jordan, the Islamic Action Front, has been the country's strongest party for decades, playing the role of a loyal opposition. Their wing in Iraq, the Islamic Party, worked with both Saddam Hussein and the American occupiers after 2003. Branches in Algeria, Bahrain, Kuwait and Yemen have maintained substantial parliamentary representation since the 1990s. The National Islamic Front, the Ikhwan's political vehicle in Sudan, backed a military coup in 1989 and was rewarded with a slew of cabinet posts. Palestine's Islamic Resistance Movement, better known by its Arabic acronym Hamas, grew out of a Brotherhood charity in the West Bank and Gaza which sought and obtained recognition from Israel in the 1970s. It beat the main nationalist Palestinian party, Fatah, in 2006's elections and then, when its reconciliation government with Fatah failed to win Western recognition, seized control of the Gaza Strip. Hamas's survival, despite Israeli attacks and global opprobrium for its resort to terrorist tactics, testifies to the Ikhwan's deep roots.

Following the Arab spring, some Western statesmen are keen to talk to the Brotherhood. Recent weeks have seen delegations rush to the gleaming new Cairo headquarters of the group's General Guide, Muhammad Badeea. The former professor of veterinary science, whose position as head of the Egyptian mother organisation carries moral authority across the region, beamed for the cameras recently as he greeted Anne Patterson, the American ambassador to Egypt, with a hearty handshake. This was doubly significant. American officials had long shunned contact with the Ikhwan. Mr Badeea's gesture also underlined the Brothers' lack of puritanical priggishness regarding women.

Does this mean that the secretive society, founded in Egypt in 1928 and a wellspring of Sunni Islamist ideology ever since, is on the verge of fulfilling a long-thwarted dream? Back in 1938 the Brotherhood's founder Hassan al-Banna, an Egyptian schoolteacher with a knack for organisation, took the podium at an Islamic gathering in Cairo and proposed stitching together the nascent states that Europe's colonial powers had carved out of the Ottoman empire. “Islam does not recognise geographical boundaries, nor does it acknowledge racial and blood differences, considering all Muslims as one umma [community],” declared Mr Banna, who enlisted hundreds of thousands of followers in six countries by the time of his assassination in 1949. Congregants, he said, should nominate a global body to elect a new Caliph, replacing the Ottoman ruler whose downfall Europe had engineered.

Ideologues still hanker after the revival of a pan-Islamic empire. “We'll have to get our respective houses in order first,” admits Jamal Hourani, a leading member of Jordan's Islamic Action Front.

To judge from a recent scene in Cairo, that may take some time. The Ikhwan is far from smugly comfortable following their sweep of Egypt's elections, even after decades of sporadic but often vicious persecution. During a huge demonstration in Tahrir Square commemorating the revolution's first anniversary last month, hecklers continually surrounded a marquee featuring Brotherhood speakers. “Beea beea ya Badeea,” they chanted, taunting Mr Badeea to “sell, sell out,” the revolution.

Despite the legitimacy conferred by success at the ballot box, Egypt's Brothers are on the defensive. Secular critics suspect them of cutting a deal with the army generals who emerged from the shadows following the fall of the old regime. In exchange for a free hand in the legislature, it is rumoured, the Brothers have quietly agreed to extend the long lease of Egypt's military-backed “deep state”. Perhaps so, but the generals also seem to distrust the Ikhwan, and show it by trying to blunt their influence wherever possible. To date, the army has coldly ignored suggestions that, as the largest block in parliament, the Brotherhood should have the right to form a coalition government.

It's hard to rule

Liberal Islamists in Egypt, meanwhile, decry the group's ideological sterility, rigid command structure and penchant for back-room politicking. More puritanical Islamists, such as the Salafists whose Nour Party came a surprisingly close second to the Ikhwan in Egypt's elections, accuse the Brothers of diluting the Islamist agenda so as to soothe Western fears. Salafists also complain of being shunned by their ostensible Islamist cousins in favour of secular potential coalition partners.

In other words, the Egyptian Brotherhood is finding that proximity to power carries a heavy tax. They are not alone. Nearly everywhere that Ikhwan-related parties have left opposition politics and entered government they have faced similar headwinds. Within a few years of Sudan's 1989 coup, General Omar Bashir, the strongman who remains in power to this day, had shunted aside his Brotherhood partners and jailed their leader. Palestinian pundits sniff that just when the Brotherhood is gaining power elsewhere, Hamas's exiled leader, Khaled Meshal, signed a deal replacing Gaza's government with one led by Fatah's leader, Mahmoud Abbas. In Kuwait and Bahrain, the sole Gulf monarchies with active, albeit highly circumscribed parliaments, the Brothers have failed to corral fellow Islamists into a united front, and have lost out to rivals with either tribal or more strongly religious appeal. For similar reasons Ikhwan-style parties have made few new converts and little electoral progress in the messy politics of Algeria, Iraq and Yemen.

Anxiety over a Brotherhood-run Arab empire should be tempered too by a better understanding of how the organisation works. The Ikhwan have a tanzim alami, or global organisation, comprised of at least two representatives from each of many Muslim communities across the world. Its nominal leader is Egypt's Supreme Guide; by tradition lesser representatives kiss his right hand. Some wishfully liken the tanzim to America's Congress, hoping that it could yet provide an institutional umbrella for a closer confederation of Arab states.

But the global Brotherhood wields little real authority. Far from applying a unified blueprint, executive offices in each country operate their own institutions with separate funding mechanisms. “The people of Mecca know their own people,” says Mahmoud Musleh, a Hamas parliamentarian in Ramallah. “Egypt cannot interfere in Palestinian affairs.” The head of Tunisia's Brotherhood-linked Nahda Party, Rachid Ghannouchi, says he will tolerate both alcohol and bikinis in his country, and his government continues to license prostitution. The Libyan chapter next door vows to continue Colonel Muammar Qaddafi's bans on all three.

Branches of the Brotherhood have clashed bitterly in the past. Iraq's invasion of Kuwait in 1990 split the global franchise into feuding pro- and anti-Iraq factions for a decade. The Syrian Brotherhood, exiled since suffering gory massacres at the hands of the country's Baathist rulers in the 1980s, long despised Hamas for maintaining its offshore headquarters in the Syrian capital, Damascus.

The Brotherhood's preparation for power has only deepened geographical divides. To prod King Abdullah into inviting them to join his government, Jordan's Brotherhood recently announced it was formally separating from its Palestinian counterpart, proof that it puts Jordan's, not Palestine's, interests first. The Hamas prime minister in Gaza, Ismail Haniyeh, has clawed control over finance away from Mr Meshal.

Lingering suspicion of the Ikhwan in Western chanceries, meanwhile, is shared by many of the Arab world's remaining autocrats. Saudi Arabia's powerful interior minister, who is next in line to the throne, castigates the Brothers for showing little gratitude for receiving refuge during past waves of persecution. He has been quoted as calling them “the source of all troubles in the Arab world”. The wealthy rulers of the United Arab Emirates maintain a quiet but effective ban on the Ikhwan.

Even now, when seeking to promote a moderate face, the Brothers look awkward or uncomfortable sharing power. Hamas's leaders in Gaza, who forcefully overthrew a national-unity government in 2007 three months into its rule, might still balk at a reconciliation agreement which would reunite Palestine's two splintered halves. Nahda, the Brotherhood chapter that won Tunisia's election, supported the nomination of a non-Islamist president yet kept key ministerial portfolios. Egypt's Ikhwan are proposing a similar arrangement.

The vaunted Turkish model

Still the Brotherhood stands out as a movement of institutions, not a figleaf for megalomaniacs. Its local chapters run internal elections and rotate their leaders. These men (and a few women) have generally proven pragmatic politicians, skilful at cutting deals when it helps them muster influence. They have sidled up to Egypt's junta and offered to serve in King Abdullah of Jordan's government, with or without elections. Across the Arab world they have professed a commitment to Turkish-style democracy, civic freedoms and free markets. To prove their belief in pluralism, Brotherhood leaders attended the most recent Christmas celebrations in Cairo's Coptic cathedral. Leaders advertise their gender sensitivity by noting that nearly a quarter of Tunisia's new parliamentarians are women, of whom 80% stood on Islamist lists. Mr Meshal recently promised a delegation of Palestinian liberals that he would add a woman for the first time to his nine-man politburo.

Besides, for all the Brotherhood's shortcomings, the region could have many worse governments. In spite of Hamas's record of terror tactics in Gaza, it has unquestionably managed the unruly Palestinian coastal strip far better than its secular predecessor Fatah. Its forces are more disciplined, the streets safer and the bureaucrats more efficient and less nepotistic. What corruption there is runs along institutional rather than blood lines. The Brotherhood's members are largely lay professionals, not clergymen, and instinctively shrink from handing clerics too much power. As for imposing sharia law, it is telling that Yousef Qaradawi, the Al Jazeera channel pundit who is the Brotherhood's preferred religious authority, recently opined that the application of God's law in Egypt needed a five year reprieve. Alas five years after taking control of Gaza, Hamas has mostly preserved existing structures and laws, with minor tweaks. Now that Israel's siege has relaxed and Hamas feels less threatened, its social controls have eased too. Though the interior minister has formally banned the mingling of genders and women smoking water-pipes in public, the new beach front resorts he has helped build sport both.

Across the region the Brotherhood has worked hard, through years of painstaking social work and uphill political battles, to enter the corridors of power. “It was like a stake tethering a water buffalo,” recounts one of the Ikhwan's new parliamentarians in Egypt, who like many of his colleagues suffered jail and exile under the previous regime. “The government kept hammering it into the ground but we just kept on digging it out.” Such patient dedication bodes well for the new rulers' ability to address the deep social and economic maladies afflicting most Arab countries. The Brotherhood's rise through the ballot box and civil action marks a hope that Islamism's reform-minded mainstream might yet prevail over the impetuous and increasingly abortive rush to arms that has characterised revolutionary Islamist groups, from the assassination of Egypt's leader Anwar Sadat in 1981 to al-Qaeda today.