Genetic research on the world's tallest land animal has found there are four distinct species of giraffe, not just one as long believed, with two of them at alarmingly low population levels.

Scientists unveiled a comprehensive genetic analysis of giraffes using DNA from 190 of the towering herbivores from across their range in Africa.

The genetic data showed four separate species of giraffes that do not interbreed in the wild inhabit various parts of the continent.

"We were extremely surprised," conservationist Julian Fennessy, co-director of the Namibia-based Giraffe Conservation Foundation, said.

Beyond genetics, the researchers identified differences among the four species including body shape, coloration and coat patterns.

Genetic differences among the four species were comparable to those between polar bears and brown bears, said geneticist Axel Janke of the Senckenberg Biodiversity and Climate Research Centre and Goethe University in Germany.

Until now, scientists had recognised a single species, with the scientific name Giraffa camelopardalis.

The study identified the four separate species as:

Southern giraffe (Giraffa giraffa), with a population of 52,000

Southern giraffe (Giraffa giraffa), with a population of 52,000 Masai giraffe (Giraffa tippelskirchi), with 32,500

Masai giraffe (Giraffa tippelskirchi), with 32,500 Reticulated giraffe (Giraffa reticulata), with 8,700

Reticulated giraffe (Giraffa reticulata), with 8,700 Northern giraffe (Giraffa camelopardalis), with 4,750

"The conservation implications are immense and our findings will hopefully help put giraffe conservation on the map," Dr Fennessy said.

Giraffe population dramatically declining

The giraffe is currently not listed as endangered, although its population has declined dramatically over the past three decades from more than 150,000 to fewer than 100,000, the researchers said.

But the low population levels of the northern giraffe and reticulated giraffe make them some of the world's most endangered large mammals and of high conservation importance, Dr Fennessy said.

Giraffes stand up to about 5.5 metres tall, with long necks and legs, a sloped back and two to five short knobs called ossicones atop the head.

They have a tan, white or yellowish coat blotched with brownish patches.

Scientists analysed 190 wild giraffes from across their range in Africa. ( Wikimedia Commons )

They roam the savannas of central, eastern and southern Africa, as far north as Chad, south to South Africa, east to Somalia and west to Niger.

Dr Fennessy said the biggest threats to the giraffe included habitat destruction due to human population growth as well as poaching for bush meat, their tail hair and "medicinal" parts.

Their closest relative is the long-necked African mammal called the okapi.

The research was published in the journal Current Biology.

Reuters