PRIMULACEAE (primula family) Contributed by David J. Bogler and George Yatskievych

Plants annual or perennial herbs. Aerial stems unbranched or branched, sometimes absent. Leaves basal and/or alternate, opposite, or whorled, sessile or relatively short-petiolate, the petiole sometimes poorly differentiated from the blade. Stipules absent. Leaf blades simple, with entire or less commonly shallowly toothed margins (pinnately dissected in Hottonia), glabrous or inconspicuously hairy, the hairs sometimes stellate. Inflorescences terminal and/or axillary, racemes, panicles, or umbels, or of solitary flowers, the flowers usually subtended by bracts. Flowers actinomorphic, hypogynous (perigynous by fusion of the ovary to the calyx tube in Samolus), perfect; cleistogamous flowers absent. Calyces shallowly to deeply (4)5(–7)-lobed, usually persistent at fruiting. Corollas shallowly to deeply (4)5(7–)-lobed (absent elsewhere), variously shaped and colored. Stamens (4)5(–7), the filaments opposite the petals, attached in the corolla tube, sometimes near the base, free (short and fused into a tube in some Primula species), the anthers exserted or not, appearing 2-locular, usually attached at or near the base, variously colored; small staminodes sometimes present, alternating with the stamens. Pistil 1 per flower, of 5 fused carpels. Ovary unlobed, 1-locular, with usually numerous ovules, the placentation free-central. Style 1, situated at the tip of the ovary, usually unbranched, the stigma usually capitate. Fruits capsules, dehiscent longitudinally by 5 valves (circumscissile in Anagallis), with few to numerous seeds. Twenty to 30 genera, about 1,000 species, nearly worldwide, most diverse in north-temperate regions.

The family Primulaceae is easily recognized by the combination of herbaceous habit, united petals, single whorl of stamens opposite the petals, valvate capsules, and free-central placentation. Primulaceae are similar to Theophrastaceae and Myrsinaceae, and these three families form a discrete lineage in phylogenetic analyses. Recent molecular studies, however, suggest that Primulaceae as traditionally circumscribed do not form a natural group, with Anagallis, Lysimachia, and several other genera allied with the Myrsinaceae, and Samolus closer to Theophrastaceae (Källersjö et al., 2000). For the present, the family is here circumscribed in the traditional sense, in anticipation of more detailed studies in the future.

The family is of relatively little economic importance, though numerous members are commonly grown as ornamentals and in rock gardens.