Smooth willowherb, smoothstem fireweed and glaucous willowherb are just three of the colloquial names used interchangeably for Epilobium glaberrimum and its two subspecies glaberrimum and fastigatum. In June Leonard and I found specimens between the North and South Elkins Barns at Ash Creek Wildlife Area (Lassen County CA). We identified them as E glaberrimum ssp glaberrimum, for which I use the common name smooth willowherb. One main characteristic of this subspecies is the lack of raised, hairy lines running down the stem from the leaf base.
A perennial native, smooth willowherb is a member of the Evening Primrose Family (Onagraceae). It is found in open, moist forests, along streambanks and other wet places between 3,000 and 11,500 feet in Washington, Oregon, California, Idaho, Nevada, Utah and Montana.
Smooth willowherb arises from a branched, scaly, tough rootstock with dark wiry roots. The erect stems are branched distally. The stems are mainly glabrous (no hairs), but may be slightly puberulent (downy) at the far end and may have a slight bloom (glaucous).
The opposite, oblong-lanceolate leaves are entire or slightly toothed. The leaves become smaller up the stem and have rounded tips. They are nearly sessile or quite sessile – no stalk or a very short stalk.
Smooth willowherb flowers occur at the stem tips. The corolla sits atop an inferior ovary. The four, notched, purplish to white petals are surrounded by four sepals. The eight stamens alternate in size, shorter stamens in between longer stamens. The stigma is four-lobed.
Smooth willowherb fruits are elongated capsules, dry and dehiscent composed of more than one carpel. The seeds have a tuft of silky hairs, called a coma, at the top.
Epilobium, the genus name, refers to the fact that flowers appear on the end of the ovary – from the Greek words “epi/upon” and “lobos/pod or capsule”. The species and subspecies designations are Latin for “no hairs”.