Euphrasia officinalis L.

Standardized Common Name: Eyebright

Family: Scrophulariaceae

Taxonomy: Euphrasia, a taxonomically difficult genus, perhaps has about 170 species. In the most recent treatments of European Euphrasia, almost 50 species are recognized. These blend into one another to such a degree that many individuals or populations are impossible to identify, and some form hybrid swarms; thus, the number of truly separate species is probably much lower. Euphrasia officinalis L., which belongs to Sect. Euphrasia, was originally applied in a broad sense that encompassed many of these. As a narrower species concept gained favor, it was asserted that E. officinalis had become an ambiguous name through its broad application. The name E. rostkoviana Hayne is therefore commonly employed for the segregate species that includes the type specimen of E. officinalis. However, this does not conform to the rules of nomenclature, and E. officinalis remains the correct name for that species. Other very similar taxa presently recognized at the specific level include E. drosocalyx Freyn, E. hirtella Jordan ex Reuter, and E. rivularis Pugsley. The traditional concept of Eyebright would have included all of these and more.

Description: Annual herb, semi-parasitic. Stem to 35 cm high, erect, slender, branching. Leaves opposite, more or less sessile, pale green, bearing glandular hairs. Leaf shape highly variable within plants: lower stem leaves from narrowly ovate-lanceolate to ovate or oblong to orbicular, 3–17 mm long; base rounded, truncate or cuneate; margins crenate or somewhat serrate with 1–7 pairs of obtuse or acute teeth; apical lobe obtuse. Upper leaves subtending flowers deltoid or ovate to orbicular; base sometimes subcordate; apical lobe often acute; marginal teeth 3–9 per side, sometimes serrate with acute to acuminate teeth, basal teeth usually dentate or backward-pointing. Flowers solitary in leaf axils. Calyx with 4 teeth; teeth narrowly triangular to linear; apices acute, acuminate or awned. Corolla bilabiate, (6.5–)8–12.5 mm long; lower lip spreading with 3 emarginate lobes; upper lip hooded, 2-lobed; white or lilac especially on upper lip, with purplish veins and yellow spots in throat and on lower lip; outside pubescent. Stamens 4; anthers spurred, contained in upper lip; filaments bent. Fruit a capsule, 4–5.5(–6.5) mm long, oblong to elliptic, apex truncate to emarginate; seeds numerous, brown.

Parts in Commerce: Whole herb

Identification:

Stem and leaves

• Stems narrow, glabrous, pale green to purplish; lower parts of stem usually with internodes longer than subtending leaves
• Leaves quite variable in shape, but larger leaves usually broadly ovate or triangular; lower stem leaves 3–17 mm long, with those at base smallest; upper floral leaves 5–15 mm long
• Leaves sessile or nearly so
• Margins with 1–9 pairs of teeth; teeth of lower leaves rounded, obtuse; teeth of floral leaves often narrower, more numerous and more acute, with basal teeth pointing outward or backward rather than forward
• Pale green, bearing multicellular glandular hairs; hairs long-stalked, with length of stalk often 10 times that of glandular head

Flowers and fruit

• Flowers solitary in axils of floral leaves
• Calyx tubular, with 4 teeth; teeth narrowly triangular to almost linear, usually long-pointed.
• Corolla (6.5–)8–12.5 mm long; lower lip flat and protruding, with 3 large lobes, apices of lobes slightly notched; upper lip hooded, with 2 smaller lobes
• Corolla whitish or lilac, sometimes with lower lip white and upper lip lilac, with purplish veins and with yellow spots in throat and one yellow spot on lower lip
• Stamens 4, contained inside upper lip of corolla
• Capsule green, oblong, 4–6.5 mm long, usually not more than twice as long as broad; apex blunt or slightly notched

E. stricta J. P. Wolff ex J. F. Lehm.: Eyebright is sometimes considered to include material from the E. officinalis and E. stricta species groups, while excluding material from species or microspecies outside these groups. As the E. stricta group is apparently not the most closely related to the E. officinalis group, nor proven to be chemically most similar, this circumscription seems difficult to justify. Linnaeus’ original specimen of E. officinalis included some material of a second species, thought to be E. stricta. Possibly E. stricta remains official today because it was thereby shown to be included within the original concept of E. officinalis, but certainly some of the excluded species or microspecies would also have fit into Linnaeus’ definition. E. stricta differs from E. officinalis in the following characters:

• Stem often stout, usually dark purple
• Leaves glossy, often dark green, with purple margins
• Leaves bearing multicellular glandular hairs whose stalks are about 5 times as long as their heads, and sometimes nonglandular hairs or bristles
• Leaves usually narrowly ovate, never approaching orbicular; most bases form short petioles
• Leaf teeth narrower, less rounded; teeth of floral leaves all forward-pointing; teeth apices acute or with small points
• Floral leaves sometimes appressed to calyx
• Calyx often purple-tinged, with black veins, margins or blotches
• Corolla almost always under 10 mm long
• Capsule over 2.5 times as long as broad, with long straight hairs

Related “species,” such as E. pectinata Ten., that grade into E. stricta usually display small variations in these and other features.

References:

Barker WR. Taxonomic studies in Euphrasia L. (Scrophulariaceae). A revised infrageneric classification, and a revision of the genus in Australia. J Adelaide Bot Gard. 1982;5:1–304.

Silverside AJ. The identity of Euphrasia officinalis L. and its nomenclatural implications. Watsonia. 1991;18:343–350.

Yeo PF. Euphrasia. In: Tutin TG, Heywood VH, Burges NA, et al., eds. Flora Europaea. Vol. 3. Cambridge: Cambridge University Press; 1972:257–266.

Yeo PF. A taxonomic revision of Euphrasia in Europe. Bot J Linn Soc. 1978;77:223–334.

Figure 26: a–d, Euphrasia officinalis; e, E. stricta.