This old variety is rarely offered nowadays but it has been in cultivation since the 19th Century. Cosmidium burridgeanum is very easy-to-grow annual with slender stems of finely cut foliage and distinctive blooms with reddish chocolate centres with tips of gold.
Flowering in twelve weeks from sowing and continuing throughout the summer, this striking annual is excellent for a mixed bed, or meadow, they are fast to bloom and keep on blooming all summer till first frosts.

Cosmidium grows 30 to 45cm (12 to 18in) tall and is somewhat similar to coreopsis in habit and care, but the flowers have more refined and uniform edges. It is an excellent addition to the cutting garden, their contrasting flowers add zing to an informal bouquet.
Sow in spring, with full sun in any well-drained moderately fertile, slightly sandy soil they are very easy to grow from seed.

Sowing: Sow indoors February to March, or outdoors April to May
Sow indoors in early spring 6 to 8 weeks before the last frost date is due. Plant outside after all risk of frosts has passed, alternatively, the seed can also be sown directly where they are to flower in mid to late spring. Keep soil moderately moist during germination. Germination 10 to 14 days at 10 to 16°C (50 to 60°F)

Sowing Indoors:
Use well drained soil and sow at a depth of 3mm (1/8in). Barely cover the seeds with sifted soil or vermiculite, as the seeds need light to germinate
Water from the base of the pots, never on top of the seeds and keep moist.
When large enough to handle, transplant the seedlings into small pots to grow on. After all risk of frost has passed, acclimatise to outdoor conditions for 10 to 15 days before planting out 50cm (20in) apart.

Sowing Direct:
Prepare the ground well and rake to a fine tilth. If sowing more than one annual in the same bed, mark the sowing areas with a ring of sand and label. Sow 1mm (1/18th in) deep in rows 30cm (12in) apart.
Sow seed sparingly or they will choke out other seedlings. Water gently and ensure that they are moist at all times
The seedlings will appear in rows approx 6 to 8 weeks after planting and can be easily told from nearby weed seedlings. Thin the seedlings out so they are finally 30cm (12in) apart. Carefully replant thinned plants.

Cultivation:
Do not apply large doses of fertiliser as flowering will be suppressed.
Keep weeded and water regularly in dry spells. Stake for cut flowers, or where exposed to wind.
Dead-heading helps improve plants appearance and prolongs flowering and encourage new flower buds. Once flowering in over leave a few plants to die down and self seed. Others can be pulled up and composted

Plant Uses:
Cottage/Informal Gardens, Flowers Borders and Beds. Cut Flowers.

Origin:
The species Cosmidium has been cultivated in English gardens since the nineteenth century. It was once thought to be a hybrid raised by one F.K. Burridge of Colchester but it was not until 1928 that it was discovered growing wild in Texas.

Nomenclature:
Cosmidium, like Cosmos is derived from the Greek kosmos, the word for harmony or ordered, or balanced universe. The species name burridgeanum is named after the nursery F.K. Burridge of Colchester where it was thought to have been developed.
Cosmidium burridgeanum is also known by the synonyms Cosmidium thelesperma and Thelesperma burridgeanum.
Thelesperma is from the Greek thele meaning ‘nipple’, and sperma meaning ‘seed’, and refers to the roughened achenes. (a type of pod that holds the seeds)
Although Cosmidium is one of the few flowers that does not really have a common name and is generally commonly known simply as Cosmidium, it is occasionally known as "Greenthreads" referring to the slender stems of finely cut foliage. It is also known as Burridges Greenthread.

Cosmidium is closely related to Coreopsis and is occasionally referred to as Coreopsis atrosanguinea. The word “atro” is a prefix conveying the sense of "blackish or very dark," and “sanguinea” is taken from the Latin sanguis meaning blood, referring to the colour, so atrosanguinea means “dark red” or “blood red”
The prefix is also used to describe other colours of flowers, atrocaeruleus means "dark blue," atrococcineus, "dark scarlet," and atropurpureus, "dark purple".