Primulaceae

The Primulaceae, 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 favorite garden plants and wildflowers. Most are perennial though some species, such as scarlet pimpernel, are annuals. It includes the former families Myrsinaceae, Theophrastaceae and Maesaceae. Primulaceae is one of 22 families in the order Ericales. Formerly, this order included some closely related families: Myrsinaceae (myrsine family), Theophrastaceae and Maesaceae (which contained only one genus, Maesa). However, morphological and molecular data strongly support their membership in the primuloid clade, which corresponds to the Primulales order in the 1981 Cronquist system. The four families have been re-circumscribed into a more broadly defined family referred to as Primulaceae s. l. The two uniting features of this clade are a free central placenta and one stamen opposite each of the corolla lobes. Below is a proposed cladogram for Primulaceae s.l. based on genetic analyses. The names on the branches correspond to the older family definitions. In 2016, estimates of the number of genera and species were 53 and 2790, but as of 2017 there were 55 accepted genera: 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. Each flower is bisexual, having both stamens and carpels. They have radial symmetry; the petals can be separate or partially or fully fused together to form a tube-shaped corolla that opens up at the mouth to form a bell-like shape (as in item 8 in the figure) or a flat-faced flower. In most of the families of Ericales, stamens alternate with lobes, but in Primulaceae there is a stamen opposite each petal. The calyx has 4 to 9 lobes and persists after flowering. They are grouped in unbranched, indeterminate clusters such as racemes, spikes, corymbs or umbels.