12. Galium tinctorium L. (southern three-lobed bedstraw)

G. tinctorium ssp. floridanum (Wiegand) Puff

G. tinctorium var. floridanum Wiegand

G. claytonii Michx.

G. trifidum L. ssp. tinctorium (L.) H. Hara

Pl. 549 a, b; Map 2546

Plants perennial. Stems 15–50 cm long, spreading to loosely ascending, weak and often trailing, clambering on other vegetation, and/or matted, usually well-branched, pubescent with short, spreading hairs at the nodes, otherwise glabrous or rarely sparsely roughened with minute, downward-angled hairs on the angles. Leaves 4–6 per node, more or less spreading in orientation. Leaf blades 5–20 mm long, 1–5 mm wide, narrowly elliptic to narrowly oblanceolate or linear, rounded or angled to a bluntly pointed tip, the midvein not extended into a point, angled at the base, the undersurface not glandular, glabrous or sparsely roughened with minute, stout, pricklelike hairs along the midvein, the venation with only the midvein visible, the margins glabrous or roughened with minute, ascending to spreading hairs, slightly to moderately curled under. Inflorescences terminal and usually also axillary from the upper leaves, not pendant, positioned over the leaves, usually consisting of small (0.5–1.5 cm long), stalked clusters. Flowers 2 or 3, rarely solitary, the stalks 1–10 mm long. Corollas 0.8–1.2 mm long, 3- or less commonly 4-lobed (the number often variable on a single plant), white. Fruits 1.5–2.0 mm long, 2.5–3.0 mm wide, the surface glabrous, smooth. 2n=24. May–September.

Scattered, mostly south of the Missouri River, most abundantly in the eastern half of the state (eastern U.S. west to Minnesota, Nebraska, and Texas; Canada, Europe, Asia). Bottomland forests, swamps, margins of ponds, lakes, sinkhole ponds, and oxbows, marshes, fens, sloughs, bottomland prairies, mesic swales of upland prairies, and seepy ledges of bluffs; also ditches.

Galium tinctorium can be distinguished vegetatively from some other Galium species by its stem nodes that are surrounded with a ring of spreading pubescence. This feature is also found in G. asprellum, G. boreale, G. concinnum, and G. obtusum. Puff (1976) noted that historically G. tinctorium was sometimes confused with G. obtusum, both because of misdeterminations and because of misapplication of the names. The two species can be difficult to distinguish, especially without mature flowers. Steyermark (1963) noted the existence of at least one apparently intermediate specimen from Wayne County. Galium tinctorium also has sometimes been considered part of the closely related G. trifidum (northern three-lobed bedstraw), a circumboreal species that is widely distributed in the United States, but in the Midwest occurs mainly to the north of Missouri. Galium trifidum might plausibly be discovered in northern Missouri in the future; it differs in its mostly solitary flowers developing curved (vs. straight) and often roughened (vs. smooth) stalks at fruiting, as well as leaves mostly in whorls of 4.

Puff (1976) recognized two subspecies within G. tinctorium. The ssp. floridanum was said to differ in its longer fruit stalks, slightly larger mericarps, more densely branched inflorescences, and more robust habit. Plants with this morphology grow in the southeastern United States west to Missouri and Texas. However, Puff himself discussed the broad morphological overlap between the two taxa and the gradual replacement of plants with the ssp. floridanum morphology by plants with the ssp. tinctorium morphology. Maintenance of these infraspecific taxa does not seem warranted.