Which of the spices is the world's most expensive spice as for the price per weight?

Saffron is a spice derived from the flower of 'Crocus sativus'. The vivid crimson stigma and styles, called threads, are collected and dried for use mainly as a seasoning and colouring agent in food. Saffron has long been the world's most costly spice by weight. Although some doubts remain on its origin, it is believed that saffron originated in Iran.

Saffron's taste and iodoform-like or hay-like fragrance result from the phytochemicals picrocrocin and safranal. It also contains a carotenoid pigment, crocin, which imparts a rich golden-yellow hue to dishes and textiles.

In the 21st century, Iran produces some 90% of the world total for saffron. At US $5,000 per kg or higher, saffron is the world's most expensive spice.