This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", 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..
Erect or diffuse, usually tufted herbs, with opposite entire often ciliate leaves, and small blue purple or white, mostly dimorphous flowers. Calyx-tube globose or ovoid, 4-lobed, the lobes distant. Corolla funnelform or salver form, 4-lobed, the lobes valvate, the throat glabrous or pubescent. Stamens 4, inserted on the tube or throat of the corolla; anthers linear or oblong. Ovary 2-celled. Style slender; ovules numerous in each cavity; stigmas 2, linear. Capsule partly inferior, globose-didymous, or emarginate at the apex, loculicidally dehiscent above, its summit free from the calyx. Seeds few or several in each cavity, peltate, more or less concave, not angled. Seed-coat reticulate or roughened; endosperm horny; embryo club-shaped. [Named in honor of Dr. William Houston, botanist and collector in South America, died 1733.1
About 25 species, natives of North America and Mexico. Type species: Houstonia coerulea L.
* Plants 1'-7' high; peduncles 1-flowered, † Peduncles filiform, 1'-2 1/2' long. Erect; leaves obovate or spatulate, narrowed into petioles.
1. H. coerulea.
Diftuse or spreading; leaves nearly orbicular.
2. H. serpyllifolia.
Calyx-lobes narrow, about equalling the capsule.
3. H. patens.
Calyx-lobes broad, much exceeding the capsule.
4. H. minima.
** Plants 4'-18' high; flowers cymose. Calyx-lobes lanceolate-subulate, 2 to 3 times as long as the capsule.
5. H. lanceolata.
Calyx-lobes linear-subulate, scarcely longer than the capsule. Leaves broad, ovate, or ovate-lanceolate.
6. H. purpurea.
Leaves oblong or spatulate, ciliate.
7. H. ciliolata.
Leaves linear-lanceolate or oblanceolate, not ciliate.
8. H. longifolia.
Leaves filiform or narrowly linear.
Flowers loosely cymose on filiform pedicels; leaves not fascicled.
9. H. tenuifolia.
Flowers densely cymose on very short pedicels; leaves usually fascicled.
10. H. angustifolia.
Houstonia coerulea L. Sp. Pl. 105. 1753. Hedyotis coerulea Hook. Fl. Bor. Am. 1: 286.
1833. Oldenlandia coerulea A. Gray, Man. Ed. 2, 174. 1856.
Erect, 3'-7' high, glabrous, or nearly so, perennial by slender rootstocks and forming dense tufts. Lower and basal leaves spatulate or oblanceolate, about 6" long, sometimes hirsute or ciliate, narrowed into a petiole, the upper oblong, sessile; flowers solitary on filiform terminal and axillary peduncles; corolla salverform, violet, blue, or white with a yellow center, 4"-6" broad, its tube slender and about the length of the lobes or longer; capsule didymous, compressed, about 2" broad and broader than long, the upper half free from the calyx and shorter than its lobes.
In open grassy places, or on wet rocks, Miquelon and Nova Scotia to Quebec, New York, Michigan, Georgia, Alabama, Tennessee and Missouri. April-July, or producing a few flowers through the summer. Includes several races. Called also quaker-ladies, quakerbonnets, Venus -pride. Bright eyes. Angel-eyes. Blue-eyed-grass or -babies. Wild forget-me-not. Nuns. Star-of-Bethlehem. Little washerwoman.