PRIMULACEAE, in botany, a family of gamopetalous dicotyledons belonging to the order Primulales and containing 25 genera with about 55o species. It is cosmopolitan in distribu tion, but the majority of the species are confined to the temperate and colder parts of the northern hemisphere and many are arctic or alpine. Nine genera are represented in the British flora.
The plants are herbs, sometimes annual as in pimpernel (Ana gallis arvensis), but generally perennial as in Primula, where the plant persists by means of a sympodial rhizome, or in Cyclamen by means of a tuber formed from the swollen hypocotyl. The leaves form a radical rosette as in Primula (primrose, cowslip, etc.), or there is a well-developed aerial stem which is erect, as in species of Lysimachia, or creeping, as in Lysimachia Nummularia (creeping jenny or money-wort). Hottonia (water violet) is a float ing water plant with submerged leaves cut into fine linear segments. The leaves are generally simple, often with a toothed margin ; their arrangement is alternate, opposite or whorled. The flowers are solitary in the leaf-axils as in pimpernel, money-wort, etc., or umbelled as in primrose, where the umbel is sessile, and cow slip, where it is stalked, or in racemes or spikes as in species of Lysimachia. Each flower is subtended by a bract, but there are no bracteoles, and corresponding with the absence of the latter the two first developed sepals stand right and left. The flowers are hermaphrodite and regular with parts in fives (pentamerous) throughout, though exceptions from the pentamerous arrange ment occur. The sepals are leafy and persistent ; the corolla is
generally divided into a longer or shorter tube and a limb which is spreading, as in primrose, or reflexed, as in Cyclamen; in Sol danella it is bell-shaped ; in Lysimachia the tube is often very short, the petals appearing almost free; in Glaux the petals are absent. The five stamens spring from the corolla-tube and are opposite to its lobes ; this anomalous position is generally ex plained by assuming that an outer whorl of stamens opposite the sepals has disappeared, though sometimes represented by scales as in Samolus and Soldanella. The superior ovary—half-inferior in Samolus—bears a simple style ending in a capitate entire stigma, and contains a free-central placenta bearing generally a large number of ovules, which are exceptional in the group Sym petalae in having two integuments. The fruit is a capsule de hiscing by five, sometimes ten, teeth or valves, or sometimes trans versely (a pyxidium) as in Anagallis.
Cross pollination is often favoured by dimorphism of the flower, as shown in species of Primula. The two forms have long and short styles respectively, the stamens occupying correspond ing positions half-way down or at the mouth of the corolla-tube ; the long-styled flowers have smaller pollen-grains, which corre spond with smaller stigmatic papillae on the short styles (see