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..
Annual or perennial herbs, with 4-angled slender stems and branches, apparently verticil-late leaves, and small white, green, yellow or purple flowers, mostly in axillary or terminal cymes or panicles, the pedicels usually jointed with the calyx. Flowers perfect, or in some species dioecious. Calyx-tube ovoid or globose, the limb minutely toothed, or none. Corolla rotate, 4-lobed (rarely 3-lobed). Stamens 4, rarely 3; filaments short; anthers exserted. Ovary 2-celled; ovules 1 in each cavity. Styles 2, short; stigmas capitate. Fruit didymous, dry or fleshy, smooth, tuberculate, or hispid, separating into 2 indehiscent carpels, or sometimes only 1 of the carpels maturing. Seed convex oh the back, concave on the face, or spherical and hollow; endosperm horny; embryo curved; cotyledons foliaceous. [Greek, milk, from the use of G. verum for curdling.]
About 250 species, of wide geographic distribution. Besides the following, some 35 others occur in the southern and western parts of North America. The leaves are really opposite, the intervening members of the ventricles being stipules. Type species: Galium Mollugo L.
I. Fruit dry.
A. Flowers yellow.
1. G. verum.
B. Flowers white, green or purple. 1. Annuals.
Flowers in axillary cymules, or panicled. Fruit granular or tubercled, not bristly.
Fruit slightly granular, or smooth, 1 mm. broad; pedicels not recurved; stem very slender.
2. G. parisiense.
Fruit granular-tubercled, 3 mm. broad; fruiting pedicels recurved: stem stout.
3. G. tricorne.
Fruit densely bristly-hispid.
Cymes few-flowered; leaves 2-8 cm. long: fruit fully 4 mm. broad.
4. G. Aparine.
Cymes mostly several-flowered; leaves 1-2.5 cm. long; fruit smaller.
5. G. Vaillantii.
Flowers solitary in the axils, subtended by 2 foliaceous bracts: fruit bristly.
6. G. virgatum.
* Fruit bristly hispid.
a. Leaves in 4's , 1-nerved.
7. G. pilosum.
a. Leaves in 4 s, 3-nerved.
Leaves lanceolate, oval, or ovate; flowers in open cymes. Upper leaves lanceolate to ovate-lanceolate, acuminate.
8. G. lanceolatum.
Upper leaves ovate, oblong, oval, ovate-lanceolate or obovate, obtuse.
Corolla usually hirsute; plant mostly pubescent; leaves oblong to ovate-lanceolate.
9. G. circaezans.
Corolla glabrous; plant little pubescent; some leaves obovate.
10. G. kamtschaticum.
Leaves linear to lanceolate; flowers in terminal panicles.
11. G. boreale.
c. Leaves in 6's.
12. G. triflorum.
** Fruit smooth or warty. † Flowers brown-purple.
Leaves lanceolate, 3-nerved: fruit smooth.
13. G. latifolium.
Leaves narrowly lanceolate, 1-nerved; fruit warty.
14. G. arkansanum †† Flowers white or greenish.
Stems smooth; introduced species.
Leaves linear to oblanceolate, cuspidate.
15. G. Mollugo.
Leaves lanceolate, acuminate.
16. G. sylvaticum.
Stems mostly more or less retrorsely scabrous; native species. Leaves obtuse; stems slightly scabrous. Plants of wet soil, not shining.
Flowers solitary, or few in small simple cymes. Corolla-lobes mostly 4, acute.
Fruit 1 1/2" in diameter; leaves ascending or spreading.
17. G. tinctorium.
Fruit 1/2" in diameter; leaves mostly reflexed.
18. G. labradoricum.
Corolla-lobes mostly 3, obtuse.
Pedicels rough, curved; flowers mostly solitary.
19. G. trifidum.
Pedicels smooth, straight; flowers 2 or 3 together.
20. G. Claytoni.
Flowers numerous in forked cymes.
21. G. palustre.
Shining plant of dry woodlands.
22. G. concinnum.
Leaves cuspidate-acute; stems retrorsely hispid.
23. G. asprellum.
11.. Fruit fleshy.
24. G. bermudense.