Chamaenerion Ség., 1754

Luo, Yike & Xie, Lei, 2023, A checklist of Onagraceae in the Pan-Himalaya region, Phytotaxa 597 (4), pp. 245-268 : 247

1. Chamaenerion Ség. , pro parte.

Lectotype (designated by Pfeiffer 1873):— Chamaenerion angustifolium ( Linnaeus 1753: 347) Scopoli (1772: 271) .

≡ Epilobium angustifolium L.

= Epilobium subg. Chamerion Rafinesque (1818: 266) . ≡ Chamerion (Raf.) Raf. ex Holub (1972: 85) .

Type:— Epilobium amenum Rafinesque (1818: 266) .

Herbs perennial, erect. Stems usually simple, rarely branched, glabrous or strigillose. Leaves subsessile, alternate, spirally arranged, rarely subopposite or subverticillate; the underground blades scalelike; the basal blades small, triangular-ovate to lanceolate; cauline blades linear to lanceolate to elliptic, often subcoriaceous. Inflorescence simple, raceme or spikelike, rarely branched. Flowers somewhat zygomorphic, 4-merous; floral tube absent, nectar at base of style and stamens; petals pink, purple, or rarely white, without a lobe; stamens 8, subequal; pollen in monads; style erect when stigma deflexed; stigma deeply 4-lobed, receptive on inner surfaces with multicellular papillae. Fruit capsulate, slender, 4-loculed, loculicidal. Seeds many, with terminal coma of silky hairs. 2 n = 36, 72, and 108 ( Chen et al. 1992).

The genus Chamaenerion , comprising eight species (nine taxa), is divided into two sections ( Tacik 1959), sect. Chamaenerion and sect. Rosmarinifolium Tacik (1959: 254). All species are restricted to the northern hemisphere, and four of them are in the Pan-Himalaya region. This genus was previously included in Epilobium . However, molecular analysis provided strong support (100% BS) for Chamaenerion as a monophyletic group sister to Epilobium ( Baum et al. 1994) . Therefore, taxonomists divided Epilobium s. l. into two genera, Epilobium and Chamerion ( Chen et al. 1992, Wagner et al. 2007). Sennikov (2011) agreed this treatment but proposed that Chamerion was the later heterotypic synonym of Chamaenerion .

Key to species of Chamaenerion in the Pan-Himalaya region

1 Bracts much shorter than cauline leaves; leaves linear to lanceolate, submarginal vein distinctly; seeds with inconspicuous chalazal collar................................................................................................................................................................... 1.1. C. angustifolium

- Bracts about half the length of cauline leaves; leaves narrowly ovate or elliptic to lanceolate-elliptic, submarginal vein inconspicuous; seeds with distinct chalazal collar ......................................................................................................................................................2

2 Stems subglabrous to sparsely strigillose, only rarely densely strigillose; primary leaf veins obscure; seeds 1.2–2.1 mm; style glabrous .................................................................................................................................................................... 1.2. C. latifolium

- Stems densely strigillose; primary leaf veins distinct; seeds 1–1.3 mm; style pubescent on lower half ...........................................3

3 Secondary leaf veins conspicuously reticulate or anastomosing; plants 30–120 cm tall; sepals 11–15 mm; petals 8–14 mm ........... ...............................................................................................................................................................................1.4. C. conspersum

- Secondary leaf not conspicuously anastomosing; plants 20–45 cm tall; sepals 15–20 mm; petals 17–25 mm ...... 1.3. C. speciosum