Factbox: Africa's Longest-Ruling LeadersDAKAR (Reuters) - Guinea holds a constitutional referendum on Sunday that could allow President Alpha Conde to rule for 12 more years after his second term expires in December. While longer than Guinea’s vocal opposition would like, the potential 22-year tenure that would mean for Conde still pales in comparison with those of many other African leaders. Here are the longest-serving heads of state on the continent. * EQUATORIAL GUINEA - Teodoro Obiang (1979-present) Obiang, 77, seized power in a 1979 coup from his uncle, who was later executed by firing squad. He has held onto power ever since, relying on repression of political opponents and revenues from the country’s offshore oil reserves. * CAMEROON - Paul Biya (1982-present) Biya, 87, took over in 1982 from President Ahmadou Ahidjo and has won a series of elections, most recently a 2018 vote that his opponents called fraudulent. * UGANDA - Yoweri Museveni (1986-present) Museveni, 75, declared himself president in January 1986 when he seized Kampala after a five-year guerrilla struggle. The ruling party endorsed him as its candidate in the 2021 election after he scrapped a 75-year age limit that would have barred him from standing again. * CONGO REPUBLIC - Denis Sassou Nguesso (1979-92, 1997-present) Sassou Nguesso, 76, assumed office in 1979 before losing the country’s first multi-party elections in 1992. He regained power in 1997 after a brief civil war and changed the constitution in 2015 to let himself stand again for re-election the following year. * eSWATINI - King Mswati III (1986-present) Sub-Saharan Africa’s last absolute monarch, Mswati, 51, was crowned in April 1986. Political parties have been banned in eSwatini, previously known as Swaziland, since 1973. * CHAD - Idriss Deby (1990-present) Deby, 67, took power at the head of an armed rebellion. He abolished presidential term limits in 2005 before reimposing a two-term limit in 2018. It will not be applied retroactively, however, meaning he could serve two terms after the next election in 2021. * ERITREA - Isaias Afwerki (1993-present) Afwerki, 74, has ruled Eritrea since it gained independence from Ethiopia. There have never been national elections in Eritrea, which rights groups consider one of the most repressive states in the world. * DJIBOUTI - Ismail Omar Guelleh (1999-present) Guelleh, 72, was handpicked to succeed his uncle, independence leader Hassan Gouled Aptidon. He was elected to a fourth five-year term in 2016. * MOROCCO - King Mohammed VI (1999-present) Mohammed VI, 56, was crowned when his father, Hassan II, died of a heart attack. The Moroccan royal family has reigned since 1631, making it the Muslim world’s oldest dynasty. * RWANDA - Paul Kagame (2000-present) Kagame, 62, was widely seen as the real power in Rwanda after leading the rebel army that ended the 1994 genocide. He was formally elected president by the national assembly in 2000 and changed the constitution in 2015 to extend term limits, a move that could let him stay in power until 2034. Reporting by Aaron Ross; Editing by Peter Cooney, Alessandra Prentice