Oenothera L., 1753

Luo, Yike & Xie, Lei, 2023, A checklist of Onagraceae in the Pan-Himalaya region, Phytotaxa 597 (4), pp. 245-268 : 263-264

5. Oenothera L.

Lectotype (designated by Rose 1905):— Oenothera biennis Linnaeus (1753: 346) .

Herbs, annual, biennial, or perennial. Leaves alternate, usually with a basal rosette that often absent after mature. Flowers opening near sunset or near sunrise, hermaphroditic, actinomorphic; floral tube well developed; sepals 4, reflexed individually or as a unit; petals 4, vary in color; stamens 8, subequal or in 2 unequal series; ovary with 4 locules, ovules numerous; style glabrous or pubescent; stigma deeply 4 linear lobes. Capsule usually loculicidally dehiscent, sessile, occasionally pedicellate, or sometimes with sterile basal stipe. Seeds usually numerous, in one to several rows or in clusters in each locule. Chromosome number: 2 n = 14, 28, 42, and 56 ( Wagner et al. 2007).

Oenothera , with 145 species (188 taxa), has been currently divided into 18 sections ( Wagner et al. 2007). It is the second largest genus in the Onagraceae . There are about five species in the Pan-Himalaya region, all of which are cultivated or naturalized.

Key to species of Oenothera in the Pan-Himalaya region

1 Flower white, pink or purple; capsule clavate or obovoid, winged or ridged; seed in indistinct rows or clusters in each locule .....2

- Flower yellow; capsule lanceoloid or cylingdric; seeds in two rows in each locule..........................................................................3

2 Petals 16–38 mm, white, or tinged with rose-purple; sepals 16–32 mm ..................................................................5.5. O. tetraptera

- Petals 5–12 mm, pink to rose purple; sepals 5–10 mm ................................................................................................... 5.3. O. rosea

3 Leaves sessile or shortly petiolate, base rounded or cordate..........................................................................................5.4. O. stricta

- Leaves more or less petiolate, base cuneate .......................................................................................................................................4

4 Stigma elevated above anthers at anthesis; petals 35–50 mm ............................................................................... 5.2. O. glazioviana

- Stigma surrounded by anthers at anthesis; petals 7–25(–30) mm ................................................................................ 5.1. O. biennis