Cosmos atrosanguineus, the chocolate cosmos, is a species of Cosmos, native to Mexico. It has often been claimed that it is extinct in the wild; however, it is "quite abundant" in Mexico. The species was introduced into cultivation in 1885 when the British seed company Thompson & Morgan first listed it in their seed catalog. It's a dark red to brownish red flowers have a scent resembling chocolate, which is one reason for its popularity as a cultivated plant.
Cosmos atrosanguineus is a herbaceous perennial plant growing to 40–60 cm tall, with a fleshy tuberous root. The leaves are 7–15 cm long, pinnate, with leaflets 2–5 cm long. The flowers are produced in a capitulum 3–4.5 cm diameter, dark red to maroon-dark brown, with a ring of six to ten (usually eight) broad ray florets and a center of disc florets; they have a light vanillin fragrance (like many chocolates), which becomes more noticeable towards the end of the day.
The species was first described in 1861 by William Hooker, as Cosmos diversifolia var. atrosanguineus. Eduard Ortgies later elevated it to a full species, placing it in the genus Bidens. Andreas Voss transferred it back to Cosmos, retaining its status as an independent species. It is one of eight species of Cosmos placed in section Discopoda. Cosmos belongs to the subtribe Coreopsidinae.
Although it had been reported that Cosmos atrosanguineus was extinct in the wild, a research project on the genus Cosmos begun in 2007 by Mexican botanist Aarón Rodríguez found modern records starting from 1986. Fieldwork showed that it grew in the states of Guanajuato, Querétaro, and San Luis Potosí. It is found in mixed pine and oak forest, at elevations of around 1,800–2,450 m (5,910–8,040 ft).