Washington, Jul 20 (IANS): Thousands of people gathered to enjoy the beauty of "bloom night", an event in a US desert in which the flowers of hundreds of cacti appear almost in unison at dusk before wilting at sunrise.

The Peniocereus greggii species of cactus, commonly known as the "Arizona queen of the night", appears dead nearly the entire year, its long, thin and spiny greyish branches having the look of dry, lifeless trunks. But shoots start appearing in the spring and turn into beautiful, radiant white flowers for one night a year, reports Efe news.

The uniqueness of this plant and its singular flowers attract nature lovers every year to Tohono Chul park on Tucson's north side.

Experts say the mass annual bloom, which this year began on Tuesday night, stems from the plant's survival instinct.

"All of the cacti bloom at the same time because they only live one night and depend on a night-flying butterfly" for pollination, Lee Mason, a representative of Tohono Chul park and expert in this plant, told Efe.

Tohono Chul is home to nearly 400 Peniocereus greggii cacti, which also are found in the desert of northern Mexico.

The mass flowering usually takes place in June, but "bloom night" in 2017 took longer than usual due to a persistent drought, high temperatures and lack of rainfall in recent months, the expert said.