Oenothera

Subgen. Oenothera . Annual or biennial. Cauline leaves up to 2 0 x 5 cm, lanceolate. Flowers nocturnal; petals yellow, often becoming purplish-red. Capsule elongate, cylindrical; seeds horizontal, sharply angled. Because of the presence of balanced combinations of lethal genes and of self-pollination in many species of this group, progenies from individual plants breed true; this has led to the establishment of many distinctive variants in Europe and a number of them have been given specific names. Any new combination of chromosomes produces, in effect, a new‘species’. Each is then characterized by a particular complex of chromosomes transmitted only through the pollen and another transmitted only through the egg. Some of the chromosome-complexes are found in more than one of these true-breeding strains, which are thus not comparable with the species recognized in any other group of flowering plants. Only the more widespread species are described here and those which seem to have originated in Europe are treated as native, although their parents were introduced deliberately or accidentally from temperate North America. It is often nearly impossible to determine dried specimens and a number of the distributions are manifestly incomplete. 1-6. O biennis group. Stem up to 300 cm, hairy. Inflorescence erect. Sepal-apices terminal, slender, appressed to one another in bud. Hypanthial tube 18-50 mm. Petals 12-60 mm. Style 3-60 mm. Capsule 10-40 mm, tapering above. Seeds 1-2-2 x 0-7-1 mm. According to the standards of Munz, N. Amer. FI. ed. 2, 5: 132-135 (1965)

, species 1 and probably 2 would be referred to O. biennis subsp. biennis ( subsp. caeciarum Munz ) and species 3 would be referred to O. biennis subsp. centralis Munz.

1 Plant greyish-pubescent; ovary and young fruit densely strigose

4. strigosa 1 Plant green or bluish-green; ovary and young fruit glandular or strigulose 2 Stem and ovaries without red spots 3 Veins of mature leaves reddish; petals 24-30 mm 1. biennis 3 Veins of mature leaves not reddish; petals more than 30 mm

6. suaveolens 2 Stem and ovaries with red spots 4 Calyx red-striped or entirely red, at least on later flowers

5. erythrosepala 4 Calyx green 5 Stem up to 200 cm, not easily detached at the base;

inflorescence-axis reddish; bracts lanceolate, weakly toothed 2. rubricaulis 5 Stem up to 300 cm, easily detached at the base;

inflorescence-axis green; bracts ovate, strongly toothed

3. chicagoensis