This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Low mostly evergreen perennials, with branched rootstocks. Leaves petioled. Flowers perfect, nearly regular, racemose, solitary or corymbose, white to red. Calyx 4-5-lobed. Corolla very deeply 4-5-parted, or of 5 petals. Stamens twice as many as the divisions of the corolla, the anthers introrse in the bud, inverted at anthesis, opening by pores or short slits; pollen-grains in 4's. Ovary superior, 4-5-celled; style short or slender, often declined; stigma 5-lobed, or 5-crenate; ovules very numerous, anatropous. Fruit a loculicidally dehiscent capsule. Seeds very numerous, minute, the loose cellular coat much larger than the almost undifferentiated embryo.
Three genera and about 20 species, natives of the northern hemisphere.
Flowers racemose; leaves basal.
Flowers solitary, corymbose or umbellate; leaves opposite or whorled.
Stem leafy at base; flower solitary; style long.
Stem horizontal; branches erect, leafy; style very short.
1. PỲROLA [Tourn.] L. Sp. Pl. 396. 1753.
Low glabrous herbs, acaulescent or nearly so, stoloniferous, perennial. Leaves basal, persistent (one northwestern species leafless). Flowers nodding, or in one species ascending, white, yellowish, pink, or purple, racemose, on erect bracted scapes. Calyx 5-parted, persistent. Petals 5, concave, sessile, deciduous. Stamens 10, declined, or straight and connivent; filaments subulate, glabrous; anthers erect in the bud, emarginate or 2-beaked at the base, mostly reversed at flowering, each sac opening by a basal but apparently apical pore. Ovary 5-celled; style straight or declined, filiform, or thickened at the summit; stigma 5-lobed. Disk usually obsolete, rarely present and 10-lobed. Capsule subglobose, 5-lobed, 5-celled, loculicidally 5-valved from the base, the valves cobwebby on the margins when opening, the apex and base intruded. [Latin, diminutive of Pyrus, pear, from the similar leaves.]
About 15 species, natives of the northern hemisphere. Besides the following, 3 others occur in western North America. Type species: Pyrola rotundifolia L.
Style and stamens declined (slightly so in no. 6).
Petals very obtuse; leaves rounded at the apex.
Leaves rounded, truncate or narrowed at the base.
Calyx-lobes oblong or lanceolate; leaves shining.
Calyx-lobes ovate or triangular, short; leaves dull.
Blades orbicular, coriaceous, mostly shorter than petioles.
Blades oval, membranous, longer than their petioles.
Flowers pink or purple; bog plant.
Leaves reniform or cordate, shining; flowers pink.
Petals and leaves acute, the latter small.
Style straight; stamens connivent.
Style short; disk none; raceme regular.
Style elongated; disk 10-lobed; flowers in a I-sided raceme.