Socotra

A third of its plants grow nowhere else on Earth

Socotra belongs to Yemen and to Africa at the same time. Administratively and culturally it is Yemeni; geologically it is a continental fragment attached to the Somali plate, isolated long enough to grow a flora that exists nowhere else. A third of its plant species are endemic, and the island is regularly called the most alien-looking place on Earth.

It sits in the Indian Ocean between the Gulf of Aden, the Guardafui Channel and the Arabian Sea, 380 kilometres south of the Arabian Peninsula and 232 kilometres east of the Horn of Africa, near major shipping routes. It is 132 kilometres long and 42 across at its widest, and it makes up about 95 per cent of the landmass of its six-island archipelago. Its people, the Socotrans, speak Arabic and Soqotri. UNESCO listed it in 2008.

The reptiles are where the endemism becomes extraordinary. Ninety-four per cent of Socotra's reptile species are found only there, and a DNA barcoding study, the most comprehensive ever done on an island group, sequenced 380 individuals covering all 31 recognised species. It found something the field notes had missed. Several species showed far more genetic variability within themselves than expected, which is the signature of cryptic diversity: separate species that look alike and have been counted as one. The authors estimate the island's true reptile richness may be underestimated by somewhere between 14 and 54 per cent.

That is a large range and an honest one. It means nobody yet knows how many kinds of animal live on Socotra, on an island 132 kilometres end to end.