Cosmos atrosanguineus

Cosmos atrosanguineus
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Asterales
Family:	Asteraceae
Genus:	Cosmos
Species:	C. atrosanguineus
Binomial name
Cosmos atrosanguineus (Hook.) Voss, not Stapf
Synonyms
Bidens atrosanguinea (Hook.) Ortgies Cosmos diversifolius var. atrosanguineus Hook.

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 catalogue. Its dark red to brownish red flowers have a scent resembling chocolate, which is one reason for its popularity as a cultivated plant.

Description

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.

Taxonomy

The species was first described in 1861 by William Hooker, as Cosmos diversifolia var. atrosanguineus. 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.

Distribution and habitat

Although it had been reported that Cosmos atrosanguineus was extinct in the wild, a research project on the genus Cosmos organized by Mexican botanist Aarón Rodríguez from 2007 onwards found records starting from 1986. Field work 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).

Cultivation and uses

Both seed-raised and vegetatively propagated cultivars are available, varying in the size, colour and shape of the petals. An article in 2017 listed 17 cultivars and seed-raised strains. The variation in flower color from red to black of Cosmos atrosanguineus and its cultivars results from variation in the amounts of anthocyanins and chalcone present.

It requires partial sun or full sun, and flowers from mid to late summer. It is frost-sensitive (Zones 6–11); in temperate zones, the tuber has to be dug up and stored in a frost-free store over the winter.