Garden marguerite

Garden marguerites, also known as marguerite daisies, are cultivars of plants in the subtribe Glebionidinae of the family Asteraceae, the great majority being hybrids created in cultivation. One of the genera belonging to the subtribe, Argyranthemum, was introduced into cultivation from the Canary Islands in the 18th century, and modern cultivars are mostly sold and grown under the genus name Argyranthemum or the species name Argyranthemum frutescens, although many are actually intergeneric hybrids. The first such hybrids involved species now placed in the genus Glebionis, but other crosses within the subtribe are known. Breeding has aimed at introducing flower heads in varied colours and shapes while retaining the shrubby habit of Argyranthemum. Garden marguerites are used as summer bedding or grown in containers. Most are only half-hardy. They can be trained into shapes such as pyramids or grown as standards.
Garden marguerites are derived from wild species in the family Asteraceae. They have the typical inflorescences of the family, in which what may appear to be a single flower is actually a composite flower head composed of many individual flowers or florets. Small tightly packed florets make up the central disc, which is surrounded by florets with longer petals (ligules), making up the rays of the complete flower head. In wild Argyranthemum species, which form the basis of garden marguerites, the flower heads have yellow centres and usually white rays, although A. maderense has pale yellow rays. Modern cultivars have much more varied flower colours and shapes. The central disc may remain yellow, be of the same colour as the ray florets, or be of a different colour. The central disc florets are enlarged in some cultivars. In fully double flower heads, the disk florets have longer petals like the ray florets. The cultivar 'Supa594' (Summersong White) has flower heads in which no central disc is visible, as all florets have ray-like petals.
Argyranthemum has a shrubby perennial habit. Cultivars may be derived from crosses with related annual species, such as Glebionis coronaria. Such crosses may produce either annual or perennial offspring, but breeders try to retain the Argyranthemum habit. Some cultivars, such as 'Sugar Button', are short-lived and are usually grown as annuals. Most are perennial, ranging in height from about 30 cm (1 ft) for the cultivar 'Snow Storm' to about 120 cm (4 ft) for the cultivar 'Starlight'.
The subtribe Glebionidinae consists of four genera, or three if Ismelia is included in Glebionis.
Hybrids between the genera are origin of many cultivars, although in some cases their parents are conjectural. Three main crosses have been documented:
The hybrid between A. frutescens and G. coronaria, named ×Glebianthemum valinianum, was discovered in Chile where both parents were naturalized and grew together.
The genus Argyranthemum is native to Macaronesia (the Canary Islands, Madeira and the Savage Islands), where about 23 species are known, although some species have been introduced worldwide. Argyranthemum frutescens was listed as being in cultivation in the Chelsea Physic Garden in a publication dated to between 1710 and 1714, although it may have been introduced earlier, as there are reports of 1699 for the Oxford Botanic Garden. Cultivated Argyranthemum frutescens reached Japan from Europe in the 1860s, with over 100 cultivars known in Japan by 1912. In the UK, the National Plant Collection for this group contained over 100 cultivars in 1993.
It was discovered in Japan in particular that Argyranthemum crosses readily with species of Glebionis (once included in Chrysanthemum). Glebionis and the related Ismelia (sometimes included in Glebionis) are found in Europe and around the Mediterranean. Intergeneric hybrids, such as the cultivar 'Izu Yellow', were known by the 1960s. The purpose of making such crosses was to produce more varied flower colours and forms along with desirable plant growth habits. Colours such as orange and reddish brown, not seen in the parents, were obtained by crossing Argyranthemum cultivars with either Ismelia carinata or Glebionis coronaria.
Because modern cultivars are often the end product of many generations of multiple crosses, determining their origin and so tracing their development is difficult. Identification of the parents of cultivars has involved both morphological characters and, more recently, genetic markers. The scent of the crushed leaves of G. coronaria is distinctive; I. carinata has more finely dissected leaves than Argyranthemum. Genetic markers were able to distinguish the different intergeneric hybrids and showed that cultivars with similar characteristics shared parents.
Cultivars probably derived from crosses between Argyranthemum and Ismelia carinata (×Argyrimelia) include:
Cultivars probably derived from crosses between Argyranthemum and Glebionis (×Glebianthemum) include:
Garden marguerites can be used as bedding, in which case they may be treated as annuals, or grown in containers. In the UK climate, they are generally half-hardy, although they may survive a few degrees of frost in a sheltered position. It is recommended that young plants should not be planted out until all danger of frost has passed. Plants can be pruned to keep them in shape, and can be trained into pyramids or standards. Propagation is by cuttings, which root easily, or in some cases by seed.
Two naturally occurring taxa and the following cultivars have gained the Royal Horticultural Society's Award of Garden Merit: