Calyx joined to ovary and often produced beyond it; petals usually 4; stamens usually 4 or 8; ovary inferior; seeds numerous.
Erect Evening-Primrose (_Œnothera heterophylla_) grows in sandy soil in Florida and on the edge of post oak woods in South-central Texas. The plants bloom in April and May. It is very much like the rhombic evening-primrose (_Œnothera rhombipetala_) but has slenderer, shorter stems and is not often branched. The petals are similar, and their rhombic shape easily distinguishes both of these plants from other evening-primroses. The rhombic primrose grows 2-3 feet high and is very abundant throughout the sandy area of North-central Texas to Minnesota and Indiana.
There are many yellow evening-primroses very much alike in flower which are usually called buttercups, a name first applied to the crowfoots. The flowers usually have four showy petals which last only a day, opening in the late afternoons and closing in the heat of the following day. The seed capsules are usually long and narrow and are borne below the petals. The fireweed is a well-known member of this group. The water evening-primrose (_Jussiæa diffusa_) is abundant in ponds in Central and East Texas.
Pink Evening-Primrose. Pink Buttercup (_Hartmannia tetraptera_) blooms best in April, but a few scattered plants may continue to bloom through the summer months. It is a perennial plant which does well in cultivation. White, pink, blush, and other shades were introduced by Childs in 1892 from seeds collected in Texas and were known as the Mexican evening-primrose.
The earlier flowers are usually much larger than those which bloom late in the season. The flowers are cup-shaped, 2-4 inches broad, with 4 broad petals marked with deeper-colored veining and greenish-yellow at the base. The sepals are united into a narrow tube above the seed capsule and below the petals. This tube is about as long as the capsule, sometimes a little shorter. The sepals do not overlap, are slow about splitting, and are pushed to one side of the flower by the opening petals. The seeds are borne in a club-shaped capsule which is prominently ridged, the slender base being as long as the enlarged seed-bearing portion.