Primula

Primula () is a genus of herbaceous flowering plants in the family Primulaceae. They include the primrose ("P. vulgaris"), a familiar wildflower of banks and verges. Other common species are "P. auricula" (auricula), "P. veris" (cowslip), and "P. elatior" (oxlip). These species and many others are valued for their ornamental flowers. They have been extensively cultivated and hybridised (in the case of the primrose, for many hundreds of years). "Primula" are native to the temperate Northern Hemisphere, south into tropical mountains in Ethiopia, Indonesia, and New Guinea, and in temperate southern South America. Almost half of the known species are from the Himalayas.
"Primula" has over 500 species in traditional treatments, and more if certain related genera are included within its circumscription.
Description.
"Primula" is a complex and varied genus, with a range of habitats from alpine slopes to boggy meadows. Plants bloom mostly during the spring, with flowers often appearing in spherical umbels on stout stems arising from basal rosettes of leaves; their flowers can be purple, yellow, red, pink, blue, or white. Some species show a white mealy bloom (farina) on various parts of the plant. Many species are adapted to alpine climates.
Taxonomy.
"Primula" was known at least as early as the mediaeval herbalists, although first formally described as a genus by Linnaeus in 1753, and later in 1754 in his "Flora Anglica". Linnaeus described seven species of "Primula". One of its earliest scientific treatments was that of Charles Darwin study of heterostyly in 1877 ("The different forms of flowers on plants of the same species"). Since then, heterostyly (and homostyly) have remained important considerations in the taxonomic classification of Primula. Primula is a member of the Primulaceae family. The most complete treatment of the family, with nearly 1000 species arranged into 22 genera, was by Pax and Knuth in 1905.
Phylogeny.
"Primula" is the largest genus in the family Primulaceae, within which it is placed in the subfamily Primuloideae, being the nominative genus.
The position of "Primula" within the family and its relationship to other genera is shown in this cladogram:
Classification.
The genus "Dodecatheon" originated from within "Primula", its species are now included in "Primula".
Sections of genus "Primula".
The classification of the genus "Primula" has been investigated by botanists for over a century. As the genus is both large and diverse (with about 430–500 species), botanists have organized the species in various sub-generic groups. The most common is division into a series of thirty sections. Some of these sections (e.g. "Vernales", "Auricula") contain many species; others contain only one.
Selected species.
Species include:
Etymology.
The word "primula" is the Latin feminine diminutive of "primus", meaning first (prime), applied to flowers that are among the first to open in spring.
Ecology.
Primulas are used as a food plant by the Duke of Burgundy butterfly.
Distribution and habitat.
Although there are over 400 species of "Primula", about 75% are found in the eastern Himalayan mountain chain and western China (Yunnan Province), constituting a centre of diversity. Other centres of diversity are a western Asian centre (Caucasus, European mountain ranges from the Pyrenees, through the Alps to the Carpathian Mountains), mountains of East Asia and those of western North America. "Primula" is found in mountainous or higher latitude zones of North America, Europe, and Asia, with extension into South America, Africa (mountains of Ethiopia) and tropical Asia (islands of Java and Sumatra). About 25 species occur in North America (represented in five sections).
"Primula" is found in the humid and moderate climate regions of the Northern Hemisphere, predominantly in the forest belt, plain meadows, Alpine lawns, and nival and meadow tundras.
Garden hybrids and cultivars.
"Primula" species have been extensively cultivated and hybridised, mainly derived from "P. elatior", "P. juliae", "P. veris" and "P. vulgaris". Polyanthus ("Primula × polyantha") is one such group of plants, which has produced a large variety of strains in all colours, usually grown as annuals or biennials and available as seeds or young plants.
Another huge range of cultivars, known as auriculas, are derived from crosses between "P. auricula" and "P. hirsuta" (among others). Specialist nurseries and auricula societies support the growing and showing of these choice strains.
AGM cultivars.
The following hybrid varieties and cultivars have gained the Royal Horticultural Society's Award of Garden Merit:-