This section is from the book "The Commonly Occurring Wild Plants Of Canada", by Henry Byron Spotton. Also available from Amazon: The Commonly Occurring Wild Plants Of Canada.
Herbs or shrubs, with opposite entire dotted leaves, and no stipules. Flowers regular, hypogynous, mostly yellow. Sepals 5, persistent. Petals 5, deciduous. Stamens mostly numerous, and usually in 3 or more clusters. Styles 3-5, sometimes united. Pod 1-5-celled. Seeds numerous.
1. Hyper'icum. Petals 5, unequal-sided, convolute in the bud, yellow.
2. Elo'des. Petals 5, equal-sided, imbricated in the bud, purplish.
L. St. John's-wort. * Pod 3-celled. Styles 3, separate. Petals with black dots.
1. H. perforatum, L. (Common St. John's-wort.) Stem much branched, producing runners at the base, slightly 2-edged. Leaves linear-oblong, with transparent dots, easily observed by holding the leaf up to the light. Petals deep yellow. Flowers in open leafy cymes. - Fields.
2. H. corymbo'sum, Muhl. (Corymbed S.) (H. macula-tum, Walt.) Stem rounded, not so branching as No. 1. Leaves with both black and transparent dots, oblong, somewhat clasping. Flowers small, pale yellow, crowded, corymbea.- Damp woods and wet places generally.
**Pod 5-celled. Styles more or less united. Stamens very many, in 5 clusters, if clustered at all.
3. H. pyramidatum, Ait. (Great St. John's-wort.) Stem 3-5 feet high. Leaves 2-3 inches long, somewhat clasping. Flowers very large, the petals about an inch long, and narrowly obovate. Stamens showy. Pod conical, large. - Along streams; not common.
4. H. Kalmia'num, L. (Kalm's S.) Shrubby, a foot or more in height; leaves linear-lanceolate, crowded, revolute on the margins, thickly punctate, and sessile. Flowers about 1 inch across, in clusters. - Niagara Falls and westward.
* * * Pod l-celled, purple.
5. H. ellip'ticum, Hook. (Elliptical-leaved S.) Stem about 1 foot high, not branched. Leaves spreading, elliptical-oblong, obtuse, thin. Flowers rather few, showy, in a nearly naked cyme. Pod purple, ovoid, obtuse. Petals pale yellow. - Banks of streams, eastward.
6. H. mu'tilum, L. (Small S.) Stem slender, branching above, hardly a foot high. Leaves 5-nerved. Cymes leafy at the base. Flowers small, not 1/4 of an inch across. - Low grounds.
7. H. Canadense, L. (Canada S.) Stem upright, 6-15 inches high, with branches erect. Leaves linear or linear-lanceolate, 3-nerved at the base, the upper ones acute, sessile. Cymes naked. Pod much longer than the calyx. Flowers small, deep yellow. - Wet, sandy places.
2. ELO'DES. Adans. Marsh St. John's-wort. E. Virgin'ica, Nutt. (E. campanulata, Pursh.) Stem smooth.Leaves oblong or oval, clasping, often purple-veined, obtuse, conspicuously dotted beneath. Flowers flesh-coloured, in the axils, and at the summit of the stem. The whole plant is of a purplish hue. - Marshes.
 
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