Primula

Primula is a genus of 400–500 species of low-growing herbs in the family Primulaceae. They include primrose, cowslip and oxlip. 

Many species are grown for their ornamental flowers. They are native to the temperate Northern Hemisphere, south into tropical mountains in Ethiopia, Indonesia and New Guinea, and in temperate southern South America.

Perennial primulas bloom mostly during the spring; their flowers can be purple, yellow, red, pink, or white. Generally, they prefer filtered sunlight. Many species are adapted to alpine climates.

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. 

Primroses are used as food plants by the larvae (caterpillars) of some Lepidoptera species.

Some flowering forms of (cultivated) Primula are commonly known as polyanthus (P. elatior hybrids) as opposite to primrose (P. vulgaris hybrids).

 Heterostyly 
The common primrose, Primula vulgaris, shows heterostyly. This is a type of morphism with flower forms which differ in the lengths of the pistil and stamens.

The morph phenotype is genetically closely linked to genes responsible for a system of self-incompatibility.'closely linked' means close together on the same chromosome. That means the pollen from a flower on one morph cannot fertilize another flower of the same morph. 

In one morph (termed 'pin') the stamens are short and the pistils are long; in the second morph (termed 'thrum') the stamens are long and the pistils are short. The length of the pistil in one morph equals the length of the stamens in the second morph, and vice versa.Darwin, Charles 1862. On the two forms, or dimorphic condition, in the species of Primula, and on their remarkable sexual relations. Journal of the Proceedings of the Linnaean Society (Botany) 6, 77–96.Darwin, Charles 1877. The different forms of flowers on plants of the same species. Murray, London. The system prevents self-fertilisation.

All sections of the genus Primula have heterostyle species, altogether 354 species out of 419.Bruun H.G. 1938. Studies on heterostyle plants 2. Svensk. Bot. Tidskr. 32, 249–260. Since heterostyly is characteristic of nearly all races or species, the system is at least as old as the genus.Darlington C. 1958. Evolution of genetic systems, 2nd ed, p120 et seq: The genetic promotion of crossing. Oliver & Boyd, London.

 References 

Category:Flowers
Category:Primulaceae