Willowherbs are mostly annual or perennial herbs, but a few are more or less partly shrubby, the perennials being mostly spreading by trailing shoots or rhizomes and sometimes producing new rosettes of leaves at their tips, or forming bulblike offsets (underground shoots). The leaves are alternate to opposite, stalkless to stalked, entire to toothed, often rather "willowlike." The flowers have both stamens and pistils, and are usually arranged in terminal, simple or compound elongated clusters, occasionally axil-borne to barely reduced leaves. The elongated floral axis below the calyx is short or lacking. There are 4 sepals. The 4 petals are white or yellowish to deep rose-purple, inversely cordate to shallowly notched at the tip. The flowers have 8 stamens. The stigma is 4-lobed or more or less oblong-club-shaped and not lobed. The fruit capsules are usually stalked, linear to slightly club-shaped, or more nearly ellipse-shaped, 4-celled, splitting open along the center of each compartment. The seeds are smooth or covered with very small bumps, and have a conspicuous hair-tuft at the tip. The genus consists of perhaps 150 species worldwide, mostly cosmopolitan. The name comes from the Greek epi, upon, and lobos, pod, referring to the ovary which is situated underneath the other flower parts.
Guide to Identify Presented Species of Genus Epilobium
FLOWERS MOSTLY OVER 2 CM ACROSS
E. angustifolium – Fireweed Perennial, 1-3 m tall, leafy, often in large colonies. Common on roadsides.
Flowers rose-purple to pink, 2-4 cm wide, with 4 broad petals, in tall clusters.
Leaves alternate, numerous, narrowly lance-shaped, stalkless and hairless.
FLOWERS SMALLER LEAVES LANCEOLATE, ELLIPTIC OR OVATE, OFTEN OVER 1 CM BROAD
E. ciliatum – Purple-Leaved Willowherb Perennial, 30-100 cm tall, branched and hairy above. Moist sites.
Flowers rose-purple to white, 5-15 mm wide, erect, with 4 notched petals.
Leaves basal and opposite, lance-shaped, 3-7 cm long, shallowly toothed.
E. hornemannii – Hornemann's Willowherb Perennial, 15-30 cm tall, stems usually simple. Moist sites, montane-alpine.
Flowers rose to violet, 8-12 mm wide, few on stem tops, with 4 notched petals.
Leaves opposite, 1.5-5 cm long, oblong, blunt-tipped, short-stalked.
