Primulaceae

The Primulaceae prɪmjəˈleɪʃiː, commonly known as the primrose family (but not related to the evening primrose family), are a family of herbaceous and woody flowering plants including some favourite garden plants and wildflowers. Most are perennial though some species, such as scarlet pimpernel, are annuals. Previously one of three families in the order Primulales, it underwent considerable generic re-alignment once molecular phylogenetic methods were used for taxonomic classification. The order was then submerged in a much enlarged order Ericales and became a greatly enlarged Primulaceae sensu lato (s.l). In this new classification of the Angiosperm Phylogeny Group, each of the Prumulales families was reduced to the rank of subfamily of Primulaceae s.l. The original Primulaceae (Primulaceae sensu stricto or s.s.) then became subfamily Primuloideae, and one genus (Maesa) was raised to the rank of a separate subfamily, making four in all. The family shares a number of characteristics, including haplostemonous flowers having the same number of petals and stamens, sympetalous corolla having the petals united, stamens opposite the petals, free central placentation, bitegmic (two layered) ovules and nuclear endosperm formation. Primulaceae are mostly herbaceous, having no woody stem, except that some form cushions (spreading mats a few inches high) and their stems are stiffened by lignin. The stems can grow upright (erect) or spread out horizontally and then turn upright (decumbent). Leaves are simple, being directly attached to the stem by a petiole (stalk), but unlike the leaves of most flowering plants they have no stipules. The petiole is short or the leaf tapers gradually towards the base. Leaf arrangement is typically alternate but some are opposite or whorled, and there is generally a rosette at the base of the stem. The edges are toothed (dentate) or sawtoothed. New leaves in the bud are usually involute (rolled towards the upper surface) or conduplicate (folded upwards), but a few species roll downwards.