Biological Flora of the British Isles: Primula vulgaris Huds. (P. acaulis (L.) Hill)

1. This account presents information on all aspects of the biology of Primula vulgaris Huds. (Primrose) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characteristics, herbivores and disease, history and conservation. 2. Primula vulgaris is a native perennial herb with a very wide distribution in the British Isles. In many lowland areas it is essentially a plant of woodlands and hedgerows, although in the west it can occur abundantly in grasslands and other communities such as heaths. In northern and western Britain and Ireland, it may be frequent in open and even exposed habitats. Its distribution is linked with soil moisture and atmospheric humidity. It is shade tolerant, but it flowers most profusely in canopy gaps. 3. Primula vulgaris is a rosette hemicryptophyte that reproduces mainly through seeds. Vegetative spread is restricted and only occurs within very short distances from the mother plant through the production of lateral rosettes. Although individual rosettes may die, plants are relatively long-lived (life expectancy of a newborn individual: 48.3 years). The mean age at first flowering was 20 months. 4. Pollination is mainly by bumblebees and other bees, but other long-tongued pollinators including syrphids, bee-flies and even butterflies may be locally important. P. vulgaris is an obligate outbreeder, with two genetically determined self-incompatible morphs ('pin' and 'thrum'). A third morph ('homostyle' or 'long homostyle'), with a stigma like that of pin but anthers like that of thrum, has been found in Somerset and North Dorset. In years when pollinators are scarce, homostyles have higher reproductive success than pins and thrums, suggesting that reproductive assurance could have had a profound effect on the evolution of homostyly in P. vulgaris. 5. Seeds are dispersed by ants and rodents. Dispersal is usually restricted to a few centimetres or decimetres from maternal plants, resulting in significant fine-scale spatial genetic structure and small neighbourhood sizes. Pollen flow, on the other hand, is more extensive, but still limited to a few metres from paternal plants. 6. Populations of P. vulgaris have not changed markedly during the last century in most parts of Britain and Ireland and it is not threatened with extinction nationally. However, there is evidence that Primroses were formerly more widespread and have decreased with the decline of coppicing and pollarding. In East Anglia, woodland populations have declined greatly in response to a series of hot, dry summers since 1970. Small, isolated populations of P. vulgaris often show reduced reproductive success, potentially affecting their long-term survival. Preservation of local habitat conditions and restoration of gene flow among populations are required to maintain viable populations of P. vulgaris in the long term.